evaluation of the sticking potential of clays to a tunnel...
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EVALUATION OF THE STICKING POTENTIAL OF CLAYS TO A TUNNEL
BORING MACHINE CUTTERHEAD
by
SEAN TOKARZ
B.S., Colorado School of Mines, 2007
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Masters of Science
Civil Engineering
2014
ii
This thesis for the Master of Science degree by
Sean Tokarz
has been approved for the
Civil Engineering Program
by
Nien Chang, Chair
Aziz Kahn
Brian Brady
May 2nd, 2014
iii
Tokarz, Sean (M.S., Civil Engineering)
Evaluation of the Sticking Potential of Clays to a Tunnel Boring Machine Cutterhead
Thesis Directed by Professor Nien Chang
ABSTRACT
In recent years there has been a trend in the tunneling industry towards underground
projects within increasingly complex geologic settings. Advancing a TBM through a
potentially adhering or “sticky” clay formation may present issues for the construction
schedule and therefore budget. Several factors influence the potential for a clay to adhere to
the excavating face of a TBM. The factor that most contributes to clay sticking potential is
the swelling capacity which is most commonly estimated from the Atterberg limits of the
clay. The other important factors is the moisture content of the sample which, assuming the
formation is below the groundwater table, typically depends on the consolidation state and
overburden history of the clay. Some other important considerations include the material
type and surficial micro-roughness of the excavation face and tooling of the TBM.
Historical studies which include interfacial testing provide a lot of information on the
mechanisms and representative constitutive models for the interfacial shear strength between
soil and construction grade steel materials. More recent studies have focused specifically on
the applications to soft ground tunneling. Multiple adhesion tests including this study and
ones performed previously indicate that thresholds for sticking potential include a surficial
roughness of greater than 2µm for stainless steel surfaces and a clay plasticity index greater
than 20 with a consistency index between 0.3 and 0.7.
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An independent testing program utilizing a ring shear device with modified top and bottom
rings is presented in detail. Results indicate good repeatability and compare well with
previous adhesion tests using modified direct shear apparatus. The relative benefit of the
ring shear device over the direct shear device is the more uniform distribution of shear
strains and the ability to test a clay to residual strengths without stopping to reverse shear
direction. The drawback is the time and attention to detail required to mold the sample into
the cylindrical chamber. Results from 19 ring shear adhesion tests indicate that maximum
previous confining pressure has a significant effect on adhesive strength and a bi-linear
Mohr Columb type strength is a representative model for the interfacial shear strength.
The form and content of this abstract are approved. I recommend its publication.
Approved: Nien Chang
v
ACKNOWLEDGEMENTS
I would like to thank my advisor for pushing me to create this original work, my family
for teaching me to never quit on the things that matter and most of all
Jamie, for keeping me going.
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TABLE OF CONTENTS
Chapter
1 Introduction ............................................................................................................................................. 1
1.1 Sticky Clays in TBM Drives ......................................................................................................... 1
1.2 Research Objectives ...................................................................................................................... 2
1.3 Testing Program ............................................................................................................................ 3
1.4 Organization of Report ................................................................................................................ 3
2 Literature Review .................................................................................................................................... 6
2.1 Soft Ground Tunneling with TBMs ........................................................................................... 6
2.1.1 Types of TBMs ................................................................................................................. 6
2.1.2 Forces on TBM Cutter Head .......................................................................................... 9
2.1.3 Clogging of TBMs .......................................................................................................... 11
2.2 Clay Mineralogy ........................................................................................................................... 12
2.2.1 Formation and Composition of Clays ......................................................................... 12
2.2.2 Surface Area and Activity of Clay Minerals ................................................................ 13
2.3 Mechanical Properties of Clays ................................................................................................. 16
2.3.1 Atterberg Limits .............................................................................................................. 16
2.3.2 Shear Strength of Clays .................................................................................................. 16
2.3.3 Adhesive Strength of Clays ........................................................................................... 17
2.3.4 Consistency of Clays & the Effects of Stress History ............................................... 20
3 Previous Studies .................................................................................................................................... 23
3.1 Historical Studies ......................................................................................................................... 23
3.2 Recent Studies.............................................................................................................................. 30
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3.3 On-Going Research .................................................................................................................... 40
4 Industry Experience and Case Studies ............................................................................................... 44
5 Description of Testing Program ......................................................................................................... 51
5.1 Previous Laboratory Testing Programs ................................................................................... 51
5.2 Clay Sample .................................................................................................................................. 52
5.3 Consolidation Testing ................................................................................................................ 54
5.4 Bromhead Ring Shear Apparatus ............................................................................................. 55
5.5 Modified Ring Shear Interface Test ......................................................................................... 56
5.5.1 Modified Ring shear Assembly Procedures: ............................................................... 60
5.5.2 Sample Preparation Procedures: ................................................................................... 60
5.5.3 Interface Ring Shear Testing Procedures: ................................................................... 63
6 Results of Testing Program ................................................................................................................. 67
6.1 Atterberg Limits .......................................................................................................................... 67
6.2 1-D Consolidation Testing ........................................................................................................ 68
6.3 Modified Ring Shear (Adhesion) Test ...................................................................................... 72
6.3.1 Interface Shear Test ....................................................................................................... 75
6.3.2 Effect of Ring Surface Roughness ............................................................................... 78
6.3.3 Effect of Over Consolidation ....................................................................................... 80
6.3.4 Consolidation During Shear Testing ........................................................................... 82
6.3.5 Interface Shear Strength ................................................................................................ 86
6.3.6 Moisture Content Measurements ................................................................................. 90
7 Summary and Conclusions .................................................................................................................. 92
7.1 Ring Shear Device Interface Testing ........................................................................................ 94
7.2 Comparison of Results from Previous Studies ....................................................................... 98
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7.3 Implications for TBM Cutter head & Excavation .............................................................. 106
8 Recommendations .............................................................................................................................. 109
References ....................................................................................................................................................... 111
Appendix
A
B
C
D
E
Manual For The Bromhead Ring Shear Apparatus………………………………………114
Specifications For Modified Steel Testing Rings…………………………………………127
1-D Consolidation Test, Laboratory Observations………………………………………131
Normally Consolidated Ring Shear Adhesion Test, Laboratory Observations……………136
Overly Consolidated Ring Shear Adhesion Test, Laboratory Observations………………164
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LIST OF TABLES
Table
1 - Comparison of typical Clay Properties – Atterberg Limits, Acitivity and Cation
Exchange Capacity ........................................................................................................................... 15
2 - Results of Consolidated Undrained and Drained Direct Shear Box Tests & Steel
Interface Shear Tests ........................................................................................................................ 25
3 - Cone Pull Out Test Results - Tensile Strength Vs. Displacement for a cone
inclination of 58 degrees and an overconsolidated clay .............................................................. 42
4 - Properties of Kaolin Clay (Old Hickory Clay Company) ........................................................ 53
5 - Summary of Atterberg Limit Tests .............................................................................................. 67
6 - Summary of Results from 1-D Consolidation Tests ................................................................. 70
7 - Summary of Results of Normally Consolidated Ring Shear Interface Tests for Top
Ring = 2µm ....................................................................................................................................... 76
8 - Summary of Results of Normally Consolidated Ring Shear Interface Tests for Top
Ring = 20µm ..................................................................................................................................... 77
9 - Summary of Results for Overly Consolidated Ring Shear Tests ............................................ 80
10 - Interface Shear Strength between Kaolin and Top Steel Ring with Roughness =
2µm 87
11 - Interface Shear Strength between Kaolin and Top Steel Ring with Roughness =
20µm ................................................................................................................................................... 87
12 - Moisture Contents Before and After Normally Consolidated Shear Testing ....................... 91
13 - Moisture Contents Before and After Overly Consolidated Shear Testing ............................ 91
14 - Consistency Index of Clay Samples Tested ................................................................................ 95
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LIST OF FIGURES
Figure
1 - Earth Pressure Balance Machines with Face Support Provided by Mechanical
Means with Compressed Air (Left) and Pressureized Bentonite Slurry (Right).
(From International Tunneling Association Mechanized Tunneling Working Group,
2000) ..................................................................................................................................................... 8
2 - Primary Forces Acting on a TBM Cutter Head in Soil ............................................................ 10
3 - Photographs Taken from Recent Projects Showing buildup of Clays in The
Working Chamber (left) and on the Cutter Head (right) of a TBM. ........................................ 12
4 - Stacking of clay molecules (from Das, 2008) ............................................................................. 13
5 - Surface activity of common clay minerals (from Lamb & Whitman, 1969) ......................... 14
6 - Adhesion Model (from Zimnik, 2000) ........................................................................................ 19
7 - Theoretical shape of adhesive shear strength envelope based on clay
microstructure and real contact area (from Kooistra, 98) .......................................................... 22
8 - Modified Lower Half of Shear Box for Adhesion Testing (from Littleton, 1976) .............. 24
9 - Stress Displacement Curves for Undrained Shear Box Tests on Normally
Consolidated Sample 1 (from Littleton, 1976) ............................................................................. 26
10 - Stress Displacement Curves for Undrained Shear Box Tests on Overconsolidated
Sample 2 (from Littleton, 1976) ..................................................................................................... 27
11 - Rmax measurements for different prepared steel surfaces (left). Photo of Prepared
Interface Ring Shear Surface for Rmax = 220μm (0.22mm) (from Yoshimi, 1981) .............. 29
12 - Test Results for Ring Shear Interface Testing Between Steel and Tonegawa Sand
for Confining Pressure = 105kPa (from Yoshimi, 1981) ........................................................... 29
13 - Coefficent of Friction between Different Sands and Prepared Steel Surface for
Confining Pressure = 105kPa (from Yoshimi, 1981) .................................................................. 30
14 - Schematic of Testing Apparatus used by Thewes to Evaluate sticking potential of
clays (Thewes, 2005) ......................................................................................................................... 31
15 - Evaluation of the Clogging Potential for Clays in Slurry Faced TBM Drives
(Thewes, 2005) .................................................................................................................................. 33
16 - Influence of Roughness in Direct Shear Adhesion Tests with Contact Time of 1-
Hour (Zimnik, 2000) ........................................................................................................................ 36
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17 - Influence of Contact Time in Direct Shear Adhesion Tests, Steel plate with
roughness of 0.2μm (Zimnik, 2000) .............................................................................................. 37
18 - Results of Modified Shear Box Tests (from Kooistra 1998) ................................................... 39
19 - Cone Pull Out Testing Apparatus, developed by InProTunnel Working Group
(from Feinendegen et al, 2010) ....................................................................................................... 41
20 - Proposed adherence Classification System based on the Cpone Pull Out Test
(from Spagnoli, 2010) ....................................................................................................................... 43
21 - Clogging Risk of Thessaloniki Metro based on the Thewes method (from Marinos,
2007) ................................................................................................................................................... 45
22 - Potential for Sticky Behavior of Cohesive Soils of Thessaloniki Metro based on
the Geodata-Torino method (from Marinos, 2007) .................................................................... 45
23 - Independent Cutter Head Used in TBM on Subway Essen Lot 34 Project (from
Waays, 1995) ...................................................................................................................................... 47
24 - Photograph of 1-Dimensional Wykham Ferrace Consolidometer ......................................... 54
25 - Photographs of Wykham Ferrace Ring Shear Apparatus ........................................................ 55
26 - Schematic of Top Steel Rings ...................................................................................................... 58
27 - Photographs of Top Stainless Steel Rings .................................................................................. 59
28 - Results of 1-D Consolidation Test for Confining Pressure = 0.25tsf ................................... 68
29 - Results of 1-D Consolidation Test for Confining Pressure = 0.5tsf ...................................... 69
30 - Results of 1-D Consolidation Test for Confining Pressure = 1.0tsf ...................................... 69
31 - Results of 1-D Consolidation Test for Confining Pressure = 0.25tsf ................................... 70
32 - Interpretation of Results from 1-D Consolidation Tests ......................................................... 71
33 - Screenshot of Proving Ring Displacement Gage from Video Recording Device ............... 72
34 - Results of Normally Consolidated Ring Shear Interface Tests for Top Ring = 2µm ......... 76
35 - Results of Normally Consolidated Ring Shear Interface Tests for Top Ring =
20µm ................................................................................................................................................... 77
36 - Comparison of Results of Normally Consolidated Ring Shear Interface Tests for
Top Ring = 2 µm & 20µm .............................................................................................................. 79
37 - Results of Overly Consolidated Tests ......................................................................................... 82
38 - Consolidation of Samples during Ring Shear for Top Ring = 2µm ....................................... 83
39 - Consolidation of Samples during Ring Shear for Top Ring = 20µm ..................................... 83
40 - Vertical Displacement of Overly Consolidated Samples ......................................................... 84
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41 - Normal Vs. Shear Stress Test Results for Top Ring Roughness = 2µm ............................... 86
42 - Normal Vs. Shear Stress Test Results for Top Ring Roughness = 20µm ............................. 87
43 - Normal Vs. Shear Stress Test Results, Peak Strengths ............................................................. 88
44 - Normal Vs. Shear Stress Test Results, Residual Strengths ...................................................... 88
45 - Location of Overly Consolidated Peak Strength Tests Relative to Normally
Consolidated Strength Envelope for Top Ring Roughness = 20µm........................................ 89
46 - Location of Overly Consolidated Residual Strength Tests Relative to Normally
Consolidated Strength Envelope for Top Ring Roughness = 20µm........................................ 90
47 - Comparison of Clay Samples from Various Studies ................................................................. 99
48 - Comparison of Test Results for Consolidated Drained Modified Direct Shear
Tests Conducted by Littleton ...................................................................................................... 101
49 - Summary of Results from Various Authors for Consolidated Drained Modified
Direct Shear Tests ......................................................................................................................... 103
1
1 Introduction
1.1 Sticky Clays in TBM Drives
The tunnel boring machine (TBM) is increasingly the method preferred by contractors and
owners to construct linear underground excavations (tunnels) in soil and soft sedimentary
rocks. With this trend and the ever evolving technology comes increased efficiency which
positively impacts construction schedule and cost, increased effectiveness at preventing third
party impacts, and increased safety for underground workers who are no longer exposed to
an excavation face without control measures. While the efficiency gained from a properly
designed and operated TBM can provide a monumental benefit to project execution, a TBM
which is not designed to suit or not properly operated for the particular ground conditions
can prove devastating to the project delivery and have negative implications for workers and
nearby residents.
The issues associated with reduced progress rates and temporary work stoppages at a
construction site are compounded in the case of tunneling. For most underground projects
the tunnel excavation is the only construction activity that can take place following initiation
of the TBM advance and installation of the final facilities cannot begin until it is complete.
In other words the excavation face is always the critical path and if advancement is hindered
or halted, so follows construction progress. This rule of the underground industry in
combination with the increasingly complexity of the tunnel boring machines and the
geological settings which are being attempted with underground methods leads to a greater
need for the geologist, geotechnical engineer, TBM designer and manufacturer, contractor
and client to have awareness of the potential issues. Additionally, since a single excavation is
typically performed with the use of only one machine, complex or changing geologic
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conditions dictate the need for a “jack of many trades” TBM capable of overcoming multiple
obstacles which may be in no way related to one another.
One such obstacle that has received increased attention in recent years is the effect of
“sticky” or “clogging” clays on TBM excavation progress. Reduced advancement rates in
large projects in Europe and the US in addition to the clogging of ill equipped TBMs on
several smaller projects has created a need for increased understanding of the phenomena
and potential mitigation techniques. Early identification in a project life-cycle and the
opportunity for avoidance of problematic geologic environments may be as important as
these reactionary mitigation techniques.
1.2 Research Objectives
The purpose of this study is to identify the contributing factors in the adherence of clays to
excavation equipment, with a focus on the cutterhead and working chamber of a TBM.
Secondly, to provide a summary of the most important research to date on the subject and
the state of the art for the identification of sticking clay potential for a TBM drive. Several
case studies have also been summarized to show how the current research relates to industry
practice. A testing program, utilizing the ring or torsion shear apparatus will be conducted to
provide some independent test results to compare with the results from previous adhesion
studies. The pros and cons of the use of the ring shear device in adhesion studies will also be
discussed. Finally, the results from previous studies and this new information will be used to
draw conclusions on the important geological and mechanical factors to TBM clogging and
compare with the current practice. Recommendations based on these findings will be
provided at the end of this report.
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1.3 Testing Program
The proposed independent testing program includes testing of a Kaolin “Boom” clay sample
with a moderate sticking potential using the simple ring torsion device. The sample was
chosen because it exhibits properties not uncommon in nature and in underground projects.
The benefits of using the ring shear device will be discussed in detail and includes a relatively
consistent distribution of strains across a sample and the ability to test a shear surface over a
(theoretically) infinite length of displacement, which is similar to the rotation of a TBM
cutter head. Two different rings with very different roughness coefficients similar to those
found on TBM excavation tools will be used for the clay-steel interface shear testing.
Additionally measurements for moisture content (consistency), atterberg limits and
consolidation parameters will be conducted to compare with shear testing results and other
studies.
1.4 Organization of Report
The report is organized into the following broad based sections with the following
objectives:
1.0 Introduction - State the subject problem and need for further study, state the
objective of the research project, summarized the proposed testing
program and how it relates to the subject matter.
2.0 Literature Review – Provide a summary of the contributing factors to TBM clogging
from the industry guidelines, discuss the types and implications of
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different clay mineralogy and provide a summary on their effects to
the mechanical properties of clays in the field.
3.0 Previous Adhesion Studies – Provide a summary of historical, recent and on-going
research into the phenomena of clay adherence to steel construction
materials. For the purposes of this report historical will refer to older
studies focused on interface testing and recent studies focused
specifically on clays adhering to TBM machinery. The summary for
each will focused on factors and results that pertain to the proposed
independent testing program and its results and conclusions.
4.0 Industry Experience & Case Studies – Provide a brief summary of notable projects from
around the world that encountered sticky clays in either the
investigation or construction phase or both. Discuss how the issue
was identified and/or mitigated both before and during construction.
5.0 Description of Testing Program – Present the proposed testing program and how the
intended methods meet the stated goals of this study. Provide
information on the clay sample and the specially prepared ring
materials used for testing. Provide details on applicable standards,
sample preparation, testing procedures and data acquisition methods.
6.0 Results of Testing Program – Present the results of the testing program in terms of the
testing program outlined in Section 5. Explain how the consolidation
and atterberg limit tests provide the parameters needed to conduct
the modified ring shear tests. Describe the results of the interface
testing in detail and provide a summary of the measured interface
strength envelopes and points.
5
7.0 Summary & Conclusions – Summarize previous testing and compare with geo-
mechanical mechanisms for clay interface shear strength. Summarize
and discuss the observations from the testing program and how the
results and interpretations apply to the soft ground tunneling
practice. Cross compare results with previous and current research
studies. Draw conclusions based on the comparisons
8.0 Recommendations – Provide recommendations for the tunnel boring machine industry
practice and for future studies.
6
2 Literature Review
2.1 Soft Ground Tunneling with TBMs
The use of Tunnel Boring Machines (TBMs) has been gaining acceptance as the preferred
method for constructing linear underground structures over the last 40 to 50 years. TBMs
are commonly used for excavating tunnels for use in transportation, water conveyance
including sewer, distribution and hydropower applications and installation of utilities
particularly in highly populated urban environments. The benefits of using a tunnel boring
machine to excavate in soft ground situations include safety, efficiency and effectiveness of
the final product. Today it is common to use a tunnel boring machine in all soft ground
tunneling projects except where the drive length is too short to justify the upfront cost of a
machine or where the geometry of the tunnel is too complicated.
2.1.1 Types of TBMs
It is important to understand the different types of TBMs used in soft ground environments
and the criteria used to choose one type of TBM over another. The basic types of soft
ground TBMs available include Shielded TBMs including open spoke type or closed shields
plate type, compressed air machines, Earth Pressure Balance Machines (EPBMs) and slurry
face machines. Open face shielded machines or “spoke” cutterheads are most common in
excavations in hard rock and are typically only used for soft ground applications in stable,
overconsolidated and thus dry clayey soils (ITA, 2000). For closed face shielded machines
mechanical support is provided to the excavation face by an almost closed cutterhead
consisting of plates located between the spokes which contain the cutting tools. Slits
between the spokes allow the excavated material to pass through the excavation chamber
into the working chamber. Closed face shielded machines are typically used in stable or non-
7
stable cohesive of mixed fine and coarse grained cohesive soils with cohesion values ranging
from 5 to 30 kN/m² (ITA, 2000). By modifying either the open or closed face TBMs or the
tunnel itself to include an air tight bulkhead compressed air can be applied to the excavation
face for using these machines below the groundwater table. Although this technique is not as
common today as the availability of EPBM and slurry machines had become more
widespread.
Earth Pressure Balance machines (EPBMs) converts the excavated material from the cutting
face into a high density slurry mix located in the working chamber which is closed off from
the remainder of the machine by a steel bulkhead. A specially designed extraction conveyor
screw maintains pressure in the working chamber while extracting the excavated material at a
controlled rate in order to maintain adequate face support. In order to maintain the
appropriate consistency of the face support mixture the excavated soil must contain a
significant proportion of fine grained material and groundwater has to be present. In some
instances additives and additional water are added into the working chamber to maintain the
consistency of the face support medium.
Slurry faced TBMs are a particular type of EPBMs in which a fluid is used to support the
excavation face. The slurry is pumped into the working chamber under pressure and the
slurry-spoil mix is pumped away from the face for separation and recycling. In order to
maintain face stability the density and viscosity of the fluid must be controlled at all times.
Typically bentonite and foam polymers are added to the slurry for this purpose. Slurry type
EPBMs are commonly used in non-cohesive soils above or below the groundwater table and
can be used in locations with high groundwater pressures such as for a lake tap. It is typically
8
preferable that the soils have a fine grained fraction of 10% or less, otherwise the excavated
spoils is difficult to separate from the slurry. Generalized schematics of the EPBM and slurry
face type machines are shown in Figure 1.
Figure 1 - Earth Pressure Balance Machines with Face Support Provided by Mechanical Means with Compressed Air (Left) and Pressureized Bentonite Slurry
(Right). (From International Tunneling Association Mechanized Tunneling Working Group, 2000)
The cutterhead of a TBM can be designed to include several different types of cutting tools
or bits. Some of these bits include teeth bits, peripheral bits, center bits, gouging bits and
wearing bits. Bits are generally made of steel or hard chip alloy which can be several times
more durable than steel and therefore more resistant to wear. Selection of the bit type, shape
and size is typically based on the geologic conditions, penetration depth, excavation speed
and the length of the drive. The wear on the cutting tools during construction can be
estimated using the following formula (ITA, 2000):
9
Where: d = amount of wear (mm)
K = Wear coefficient (mm/km)
D = Distance between center of cutterhead and bit location (m)
N = Revolutions of the cutterhead per minute (rpm)
L = Excavation Distance (m)
The wear coefficient is typically given by the manufacturer and is based on the pressure
applied to the tool against the face, the geological conditions, bit material, rate of advance
and rotational speed. The design cutter head rotational speed is inversely proportional to the
cutter head diameter to limit the velocity of the peripheral cutters. The amount of torque
required to rotate the cutter head is dependent on the amount of thrust applied at the face.
High contact pressures caused by high torque may slow or stop (stall) a machines progress.
2.1.2 Forces on TBM Cutter Head
The act of excavating a geologic formation with the use of a TBM creates active forces
caused by the construction activities and passive or reactive forces in the surrounding soil
and in its pore water. Active forces include (Festa, 2012):
Contact Pressure between the cutting wheel and the soil;
Hydrostatic pressure exerted by face support fluid;
Weight of the cutting wheel, TBM shield support fluid, and lining (typically steel or
concrete);
Longitudinal component of advance force from thrust cylinder;
Pulling force due to trailing gear;
Torque of the cutting wheel created by the cutter motor.
10
There is a slight moment arises due to the weight of the wheel which for practical purposes
can be ignored. The weight of the machine and its components is considered to have
negligible effect compared to the other driving forces and is not considered. Based on
previous studies of the data generated during slurry faced TBM operation only about 20% of
the axial force generated by the wheel displacement cylinders is actually directly transferred
to the soil (Festa, 2012). Passive forces include the soil and pore water pressure generated at
and around the excavation face as well as the shear forces generated by the drag of the
spinning cutterhead in contact with the excavation face. Of these forces the net driving force
(the thrust forces minus the drag of the machine and trailing equipment) and its resulting
contact pressures at the excavation face as well as the torque on the spinning cutting wheel
and its resulting shear forces on the soil at the excavation face will be the primary focus in
this study. A schematic of the primary forces under consideration is shown in Figure 2.
Figure 2 - Primary Forces Acting on a TBM Cutter Head in Soil
During TBM operation extremely high contact pressures are developed at the excavation
face and (due to the buildup of excavated material) inside the working chamber behind the
11
cutter head. A buildup of excess pore water pressure in the soil in front of the cutter head
will occur as a result of the net driving force. In the case of slurry faced TBM this excess
pore water pressure will be partially balanced by the hydrostatic pressures within the working
chamber (Festa, 2012).
2.1.3 Clogging of TBMs
Clogging can occur in drives with shielded machines in clayey soil, especially when using a
fluid supported tunnel face and slurry circuit mucking system. Initially transport of soil in the
cutting wheel, excavation area and suction inlet area is hindered (Thewes, 2005). If enough
material builds up than stoppages can occur.
The problem typically initiates in the suction inlet area when excavated material builds up in
front of the inlet grill. The material is then compressed by more excavated material
increasing the contact pressures at the excavation face. Eventually the working and
excavation chambers fill. Clogging can also occur in the cutting wheel area, typically towards
the center of the wheel. As a consequence, clay discs typically occur in front of the cutting
wheel. The clay has to travel from the center (or other location) to the holes in the cutter
head to pass into the working chamber. If the excavation face is in mixed cohesive and
granular soil stability problems may ensue, particularly when below the groundwater table
(flowing condition). Photographs of clogging occurance for both the working chamber and
the cutter head face are shown in Figure 3
12
Figure 3 - Photographs Taken from Recent Projects Showing buildup of Clays in The Working Chamber (left) and on the Cutter Head (right) of a TBM.
2.2 Clay Mineralogy
2.2.1 Formation and Composition of Clays
Very fine grained particles such as clays (particle diameter < 0.2microns) are a product of
weathering and commonly have a crystalline structure that contains Silicon (Potassium),
Aluminum (iron or Magnesium), Oxygen and Water (Das, 2008). The clay structure is
formed by the stacking of octahedral Mg-Al hydroxide molecules to form gibbsite (G) sheets
and tetrahedral Si-oxide molecules to form silica (S) sheets. Covalent bonds hold the ions
together in the stacked structure. In Kaolin type clays these unit layers are stacked in a one-
to-one structure. In Illite and Montmorillinite type clays the unit layes are stacked in a two to
one fashion with the hydroxide sheets separated by potassium in the Illites and by water
layers in the Montmorillinites as shown in Figure 4. Within the crystal lattice the clay layers
are held together by relatively weak Van der Walls bonds due to the polar nature of the
particles.
13
Figure 4 - Stacking of clay molecules (from Das, 2008)
The surface of every clay soil particle carries a negative charge and the extent of the charge
depends on the mineralogy. Due to the presence of the two positively charged hydrogen
atoms separated by 105˚ of rotation along one side of its particle surface water molecules
behave as a dipole. The positively charged surfaces of the water molecules attract to the
negatively charged surfaces of the clay particles. Due to the attraction and the eventual
sharing of the positively charged hydrogen atoms the clays develop what is known as an
absorbed layer of surface water. If clay particles are small and “scale-like” in shape, the
proportion of the absorbed layer by volume becomes high (Terzaghi, 1953). Additionally,
cations (typically salt minerals) trapped in the area near the clay surface will bond with the
water molecules and create a second more loosely held layer of water. Together this forms
what is known as the diffuse double layer surrounding clay particles.
2.2.2 Surface Area and Activity of Clay Minerals
The size of the diffuse double layer of clay and the intensity of its bond strength is
dependent on the surface area of the clay particles. Although numerous different types of
clays have been identified in nature three principal groups of clays referred to as
14
Montmorillonites, Illites and Kaolinites have been used to discuss the differences in clay
behavior and mineralogy and will be discussed in greater detail here. Specific surface area is a
measure of the clay particle surface area to the mass of the clay particle. All three clay types
have a laminated crystalline structure but their specific surfaces are very different. The
specific surface area of Kaolinite is about 15 m²/g, Illite 90 m²/g and montmorillonite is 800
m²/g (Das, 2008).Surface activity is a measure of the intensity of the surface charge and can
be determined experimentally as a measure of the plasticity index of soil to the percent of
clay it contains by mass. Normally active soils have an activity of about unity (Terazaghi,
1953). Kaolinites have the least activity followed by Illites which are more active and
Montmorrilonites have the most activity and also have the greatest capacity to swell by
taking water into their space lattice. A comparison of the activities of these clay types is
provided in Figure 5.
Figure 5 - Surface activity of common clay minerals (from Lamb & Whitman, 1969)
15
Activity is commonly used as an index for identifying the swelling potential of clay soils. Clay
minerals actively exchange cations (salt minerals) and water molecules both within the clay
structure and externally in the diffuse double layer. The Cation Exchange Capacity (CEC) is
a measure of the potential chemical activity of a clay. Some typical ranges for activity and
CEC along with other properties for the common types of clays is shown in Table 1. One
method used to quantify the CEC is the methylene blue spot method, assuming only the clay
fraction is responsible for cation exchange. The resulting electrostatic properties of a clay
mineral vary with both cation and water content. A way to measure the cation exchange
capacity is to measure the milli-equivalent amount of cationic dye that a 100g sample of clay
absorbs.
Table 1 - Comparison of typical Clay Properties – Atterberg Limits, Acitivity and Cation Exchange Capacity
Clay Type LL (%) PL (%) Activity CEC
(meq / 100g)
Kaolinite 10-110 25-40 0.01 – 0.5 3-15
Illite 60-120 35-60 0.5 – 1.0 10-40
Montmorillonite 100-900 50-100 1.0 – 7.5 80-150
(Data from Grim 1962, Kerr 1951, Lambe & Whitman 1969, Mitchell 1976)
A more direct way of testing for clay minerals susceptible to adhering to metal surfaces is to
use x-ray diffraction to identify mineral types within the clay.
16
2.3 Mechanical Properties of Clays
2.3.1 Atterberg Limits
As mentioned above the physical properties of clays vary greatly depending on their mineral
constituents. Particles are considered to be in a colloidal state when the particles are so small
(typically <0.1 microns) that the surface activity has appreciable influence on its behavior.
Clays have been found to behave as either a solid, a semisolid, plastically or as a liquid with
increasing moisture content (Casagrande, 1932). The range of moisture contents at which
soils behave plastically is commonly referred to as the plasticity index. Within the range for
the plastic behavior clays exhibit higher shear strength due to cohesion. Cohesion is
considered to be a colloidal property and is (likely) due to the increased shearing strength
due to the absorbed layers that separate the particles for a clay specimen within the plastic
range of moisture contents.
2.3.2 Shear Strength of Clays
In a classical strength test such as a shear box test the specimen is subject to a vertical
confining pressure and then subsequently forced to shear along a plane within the specimen
itself by the application of a horizontal load. It is common to approximate the shear strength
of the sample as a linear function dependent on the normal stress applied using the Mohr-
Coulomb failure criteria (Mohr, 1900). The failure function or envelope is defined by two
constants as follows:
Where: = shear strength of clay
17
= cohesion of clay particles
= normal load pressure applied to the clay specimen
= internal friction angle of clay
In testing of clays it is important to distinguish between total and effective stresses. Total
stresses act on the clay, water and air (unsaturated clays) composite structure and effective
stresses are those stresses which act directly on the solid clay particles themselves. To arrive
at effective stresses the value of the pore water pressure is subtracted from the total stresses.
2.3.3 Adhesive Strength of Clays
Ideal Adhesion was defined by Meyers (1991) as “the reversible work required to separate a
unit area of interface between two different materials or phases to leave two bear surfaces of
unit area”. Practical Adhesion was defined by Zimnik (2000) as “the state in which two
bodies are held together by intimate interfacial contact in such a way that mechanical force
or work can be applied across the interface without causing the bodies to separate.”
In physical terms clay adhesion is the behavior of clay in which it tends to stick to the
surface of other solid materials. Similar to the example given above for determining the
shear strength of clays the adhesive strength of clays to a given material can be determined
using a modified basic shear box apparatus. The modified testing apparatus is mentioned
here to discuss the general adhesive behavior of clay, examples of tests of this kind and the
results will be summarized later in the report. Instead of shearing a clay sample along a
predetermined plane within the sample itself the clay is sheared along a contact with a metal
18
(or other material) surface. The results can be presented in terms of a Mohr-Coulomb failure
type envelope with the addition of two new constants (Das, 2005):
Where: = interface shear strength of clay
= adhesion of clay particles to surface
= normal load pressure applied to the clay specimen
= adhesive friction angle of clay
Adhesion and adhesive friction is known to depend on the real (vs. apparent) contact surface
between the metal surface and the clay (Bowden and Tabor, 1964). The real contact surface
is dependent on the micro-roughness of the surface along with the size, shape and
orientation of the clay minerals (Kooistra, 98).
True adhesion also depends on the attractive forces between the clay mineral and the metal
surface. Consider a steel plate that is wetted and then contacted with a clay particle. Clays
with minerals of high swelling potential will absorb some of the water that builds up at the
steel clay interface. Eventually a suction pressure with a value similar to pore water pressure
will develop in the interface water. Adhesive shear strength can be described in terms of
adhesion and adhesive friction angle while adhesive tensile strength is only dependent on
adhesion. A model indicating the difference between tensile adhesion (at) and shear
adhesion (as) is shown in Figure 6.
19
Figure 6 - Adhesion Model (from Zimnik, 2000)
These values are measured using different testing apparatus. The difference between tensile
and shear adhesion will be in the real adhesion and differential fluid pressures that develop
during the different methods of testing.
In adhesive shear strength tests if the shear resistant forces of the clay to clay contacts are
greater than the resistant forces of the clay to metal contact than shearing will occur at the
metal (or other non-porous material) surface. If however, the shear resistant forces of the
clay to metal contact are greater than the forces of the clay to clay contacts near the metal
surface than sticking of the clay particles to the metal surface will occur. Therefore it is
possible to predict whether clay adherence to the metal surface will occur if the adhesion,
cohesion, adhesive friction angle, cohesive friction angle, normal and shear stresses are
known. Based on previous studies, three failure modes for adhesive interface shear have
been developed:
1. Sliding along steel clay interface
20
2. Sliding within clay sample
3. Combination of 1 & 2
Mode 3 has been shown to occur for a certain critical range of steel roughness and involves
internal deformation of the clay sample (Zimnik, 2000).
2.3.4 Consistency of Clays & the Effects of Stress History
Relative consistency is a measure of the natural moisture content of a clay specimen in
relation to the moisture content at its Liquid limit and the range of moisture contents over
which the soil behaves in a plastic manner. The equation for relative consistency is as
follows:
Using the above formula a clay sample with a relative consistency of zero will be at its liquid
limit and at a relative consistency of unity will be at its plastic limit. Henkel (1960) pointed
out that there is a unique relationship between the moisture content at failure and shear
strength of clayey soils. Platy clay particles in water will have a tendency to repel from one
another (disperse) due to their negatively charged surfaces. In oversaturated conditions the
clays will only be held together loosely by their common attraction to the molecules of water
and there will be a tendency for the particles to form a lattice like structure with the pore
spaces occupied by water. In this way the clay matrix will contain the maximum amount of
water possible (Ic = 0) and still behave as a semi-solid mass.
21
If a normal stress acting on the saturated soil mass is applied the stress will immediately be
transferred to the less compressible pore water which will in turn begin to be squeezed out
of the mass provided there is a drainage path. This can be thought of in terms of effective
stresses acting on the solid clay matrix causing the matrix to compress. The plate like
particles will begin to align in horizontal sheets since the weak van der walls forces will no
longer be enough to repel the surfaces. If the normal stress is high enough, eventually the all
of the free pore water will exit the mass leaving only the solid particles and the bonded water
(Ic = 1).
The process described in the previous paragraph is commonly referred to in soil mechanics
as consolidation. If a clay sample is removed from within the consolidated mass it will have a
tendency to lock in the previous consolidation pressures provided the moisture content is
kept constant. In this way the relative consistency and therefore the density, shear and
adhesive strength parameters of a clay sample are highly dependent on its stress history.
Field observed consistency is a measure of the consistency of clays and is commonly
described using terms ranging from very soft to very stiff (Terzaghi, 1952).
Due to plastic deformation of clays the real contact surface will also increase with increasing
normal pressure. Along with the type of clays, the degree of consolidation will have an effect
on the real contact surface area of the clay with a metal surface. Over consolidated clays that
exhibit a structure of parallel stacked plates (transverse isotropy) will have a greater real
surface area than clays with platy particles in random orientations (normally consolidated)
particularly when the stacked plates are also parallel with the metal surface. Therefore, with
increasing degree of consolidation it is expected that the adhesion will increase and that the
22
adhesive friction coefficient will decrease. A model for the increase in adhesion with
increasing normal pressure is shown in Figure 7.
Figure 7 - Theoretical shape of adhesive shear strength envelope based on clay microstructure and real contact area (from Kooistra, 98)
In addition, with increasing water content, internal and external bonded crystal water and
external free water molecules are present and adhesion is expected to decrease.
23
3 Previous Studies
3.1 Historical Studies
The adhesion limit test in addition to the more commonly used atterberg limits was
developed by Atterberg in 1911 for use in the agricultural industry. The atterberg limit tests
were not widely used in the US for identifying the behavior of fine grained soils until the
1970s. Today the testing procedures for the atterberg limits for soil are standardized under
ASTM guidelines but the adhesion limit test has been left out of the standard. The adhesion
limit or “sticky limit” is loosely defined as the lowest water content at which a soil adheres to
a nickel plated spatula when drawn lightly across the soil paste’s surface. The adhesion limit
always falls between the plastic limit and liquid limit in terms of moisture content and it
separates the range of plasticity, quantified by the plasticity index, into a sticking range (water
contents between the adhesion limit and liquid limit) and a non-sticking range (water
contents between the plastic limit and the adhesion limit). Rieke (1923) defines the limit
between the plastic limit and the sticky limit as the Rieke Index. The purpose of the index
was to establish the workability of clays for ceramic industry. A Rieke index less than 10 is
considered desirable in the ceramics industry.
Potyondy (1961) proposed expressing skin friction between various soils and construction
materials in a form similar to the mohr-columb failure envelope including an adhesion value
and a normal stress-dependant compnent. Boisson (1981) published a graph in which the
adhesion of clayey surfaces of plexiglass, leather, smooth steel and rough steel is shown. Also
noted was the importance of contact time between clay and steel. Kalachov (1975) found a
relation between the tensile adhesion and the water content. He determined the maximal
24
tensile adhesion for each normal stress at the “maximal molecular water content”, which is
the maximal amount of water bonded in the mineral Skeleton by molecular forces.
Littleton (1976) conducted a series of modified shear box tests, similar to those described
previously, to assess the adhesion of different clays to a metal surface in shear under various
confining pressures and compare with the shear strength of the clays themselves. Shear box
and modified shear box adhesion tests were conducted on specimens of kaolinite and illite
clays under unconsolidated undrained, consolidated undrained and consolidated drained
conditions (Littleton, 1976). To perform the tests a 60mm square shear box apparatus was
used. The top face of the shear block, shown in Figure 8 was ground and polished prior to
testing and the surface roughness in the direction of shear was measured before and after the
tests and the average roughness was found to be 0.18μm (0.00018mm).
Figure 8 - Modified Lower Half of Shear Box for Adhesion Testing (from Littleton, 1976)
25
Sample 1 kaolinite was prepared from powder and the Sample 2 illite obtained from a
supplier. Consolidation for the CU and CD tests were done under increasing loads as
readings were taken to ensure at least 95% consolidation had taken place prior to shearing.
The strain rate for the CD test was estimated using the method developed by Gibson and
Henkel. CU tests were conducted at the maximum apparatus speed of 0.592 mm/min. A
summary of the results from the CU and CD tests conducted by Littleton are shown in
Table 2 below:
Table 2 - Results of Consolidated Undrained and Drained Direct Shear Box Tests & Steel Interface Shear Tests
Sample
– Test
PI Peak
Friction
Angle
Peak
Adhesive
Friction
Angle
Peak
Cohesion
(N/mm²)
Residual
Friction
Angle
Residual
Adhesive
Friction
Angle
S2 – CU 33 15.0˚ - 0 12.5˚ 10.5˚
S2 – CD 33 20.0˚ 18.2˚ 0 14.0˚ 11.5˚
S1 – CU 53 14.8˚ - 0.009 - -
S1 – CD 53 19.5˚ 17.5˚ 0 14.5˚ 11.5˚
(data from Littleton, 1976)
During shearing the normally consolidated sample 1 specimens contracted. The over
consolidated sample 2 specimens dilated at a normal pressure below the pre-consolidation
pressure and contracted above the pre-consolidation pressure. The results of the drained
tests showed both clays had similar peak stresses but they occurred at different
displacements. In the undrained tests sample 1 typified the behavior of normally
consolidated clay and the sample 2 that of an over consolidated clay in which a higher peak
26
stress is followed by a constant residual stress. Displacement-Shear curves for both samples
at different confining pressures for consolidated undrained tests are shown in Figure 9 for
the normally consolidated kaolinite and Figure 10 for the overly consolidated illite. The
increasing slopes of the Sample 1 curves beyond the ultimate strength was attributed to the
additional consolidation of the sample (Littleton, 1976) beyond the yield point.
Figure 9 - Stress Displacement Curves for Undrained Shear Box Tests on Normally Consolidated Sample 1 (from Littleton, 1976)
27
Figure 10 - Stress Displacement Curves for Undrained Shear Box Tests on Overconsolidated Sample 2 (from Littleton, 1976)
In both the drained and undrained tests the adhesion of clay to steel was initially higher
(steeper slope for stress- strain) than the clay to clay cohesion. It was proposed by Littleton
that interface shear values should be reported as a percentage of total shear values.
Microscopic examination of the steel surface after testing revealed minute quantities of clay
lodged within the asperities. Observations indicate that 90% of the shearing area consisted
of clay to clay contact. It was concluded that the sharp peak stresses at small displacements
followed by residual stress (observed on illite on steel) was due to the history of over
consolidation. According to Littleton: “The results of the paper suggest that for clay-steel
experiments the most uniform adhesion factors are obtained using residual shear stress of an
over consolidated clay for displacements > 3mm.”
Interface testing of different construction materials and sands of different grain sizes was
performed by Yoshimi (1981) using the ring shear apparatus. A specially designed ring shear
28
apparatus with an inside diameter of 240mm and outside diameter of 264mm was used. A
series of stacked acrylic rings were used to confine the sample so that radiographic
observations of lead markers placed within the sample could be made. Constant normal
stress using steel weights and constant volume tests using a hydraulic jack were performed. It
was determined that shearing strain during the tests varied as much as 9% with respect to the
average due to the difference between the inside and outside radii. This value reduced
considerably after the shear surface had developed.
In one series of tests a low carbon structural steel (ASTM A36) was machined to make ring-
shaped specimens. The lower surface of each ring was finished to a different roughness
quantified in terms of maximum height (R-max) defined as the largest amplitude along a
surface profile over a 2.5mm length. The average R-max was between 3μm (0.003mm) and
0.51mm which was considered to cover the range of construction materials. A comparison
sketch of different roughness coefficents along with a photo from one of Yoshimi’srings is
shown in Figure 11. Using an X-ray camera the displacements of the embedded lead
markers were measured up to 1μm (0.001mm).
29
Figure 11 - Rmax measurements for different prepared steel surfaces (left). Photo of Prepared Interface Ring Shear Surface for Rmax = 220μm (0.22mm) (from Yoshimi,
1981)
From the radiographical observations it was concluded that the apparatus was successful at
producing uniformly distributed shear strains except in a thin zone near the metal surface.
Also, at shear stresses less than 85% of the maximum value the sand deforms uniformly
throughout its height. Test results at different roughness coefficients from the ring shear
testing on Tonegawa Sand are shown in Figure 12. Results from testing of all three samples
of sand are shown graphically on Figure 13. The coefficients of friction are primarily
governed by R-max of the metal surface, irrespective of sand density. The coefficient of
friction of a very smooth steel surface is 22 to 43% of that of a very rough steel surface. The
maximum and residual coefficients of friction are nearly equal when the surface roughness
exceeds 0.02mm. This data is in good agreement with results reported by others over an R-
max range of 0.01 to 0.02mm for steel.
Figure 12 - Test Results for Ring Shear Interface Testing Between Steel and Tonegawa Sand for Confining Pressure = 105kPa (from Yoshimi, 1981)
30
Figure 13 - Coefficent of Friction between Different Sands and Prepared Steel Surface for Confining Pressure = 105kPa (from Yoshimi, 1981)
3.2 Recent Studies
Thewes (2005) carried out a research program in order to classify clay formations in terms of
their clogging potential for EPBM drives by testing the adhesion of clay on steel. The
program was based on practical research regarding clogging potential as well as laboratory
tests with clay samples. A new test was developed in order to evaluate adhesion between a
soil sample and a steel piston when it is pulled vertically from the sample (Figure 14). The
piston surface is wetted prior to contact with the soil.
Tm
ax /
Nor
mal
For
ce
Peak (max) Residual
31
Figure 14 - Schematic of Testing Apparatus used by Thewes to Evaluate sticking potential of clays (Thewes, 2005)
Soil-mechanical and mineralogical tests were also performed for comparison with the
adhering tests. Information of grain size distribution, natural moisture content and atterberg
limits were determined. Adhesion tests were carried out with soils from six clay formations
varying in their mineralogical composition. Parameters that were varied throughout the
testing included:
Soil consistency
Wetting time before contact
Contact time
Type of wetting fluid
Normal adhesion of soil and steel proved to depend strongly on the content of swelling clay
minerals and the consistency of the clay. It was shown that normal adhesion increased
strongly with increasing consistency (stiffness). It was determined that this increase had not
been described in older research because the wetting of the contact surface prior to shearing
had not been done before. Decreased wetting time and increasing contact time led to an
32
increase in the measured adhesion. The adhesion in Kaolinite clays was comparatively low to
that of samples with swelling clay minerals.
Thewes proposed a model for the mechanisms which drive adhesion of swelling clays to
metal surfaces:
1. Soil is wetted with water under atmospheric pressure. The pore pressure in the clay
is much lower than the water. The pressure differential causes the clay to absorb the
water and the clay structure swells.
2. A steel plate is wetted and then placed into contact with the soil. There is a small
amount of water enclosed in the micro-asperities of the steel when in contact with
the soil. The pore pressure differential in the clay allows it to begin absorbing the
water. A subpressure similar to the pore water pressure in the clay develops in the
encapsulated contact water. A resulting tensile stress develops at the interface.
During the research program the construction details and geological information were
collected from several tunnel drives where adhering problems of different types and
magnitudes occurred. The machines used in the case studies were not originally designed for
clayey soils. Thewes (2005) determined that in tunneling in stiff to hard swelling clays the soil
typically has to be conditioned using as a supporting medium. In such cases foams are
typically added into the working chamber to reduce the effects of adhesion at the face. He
also observed that the mucking system which typically consists of a screw conveyor and
muck skips on trains is particularly susceptible to issues associated with adhesion.
33
Comparison of the test results with the new apparatus, mineralogical and mechanical
properties of the samples and information from the case studies led to a new simplified
classification scheme based on the ratio of the relative consistency of in-situ clay to its
plasticity index as measured in the laboratory. The chart separates the plot into three zones
of low, medium and high clogging potential with low potential leading to a reduction in
TBM advancement rates and high potential indicating significant reduction in advance and
daily cleaning of the TBM cutter head. The thewes chart is presented in Figure 15.
Figure 15 - Evaluation of the Clogging Potential for Clays in Slurry Faced TBM Drives (Thewes, 2005)
High Clogging Potential
Medium Clogging Potential
Low Clogging Potential
Soft
Medium Stiff
Stiff
Very Stiff
Hard
34
The Thewes chart is now commonly used in industry for predicting the potential for sticking
clays to be an issue during the planning stages of a project’s development. The simplicity of
the chart and the fact that it uses soil parameters that are commonly assessed at even the
earliest stages of conceptual design make it a very useful tool for engineers and owners.
Plasticity is an inherent property of a clay formation which (as shown previously) is directly
tied to clay mineralogy and correlates with clay activity. The premise of the chart is that as
the water content of a cohesive soil with a higher PI (potentially sticky) approaches the
plasticity index (Ic=1) the stiffness and the likelihood of clogging issues increase.
Following an example of the use of the Thewes method if a sample of clay has moisture
content at its plastic limit then the relative consistency of that sample is equal to unity. As
the moisture content of the sample is increased to its adhesive limit, as defined by Atterberg,
the location of the sample on the Thewes chart will move down corresponding to a relative
consistency of less than unity. If the sample’s moisture content is further increased within
the sticking zone on the atterberg chart (within the Rieke Index) the location of the sample
will continue to move down on the Thewes chart eventually into the zone of “Low Clogging
Potential”. In this way the use of the Thewes method does not correspond with classical
adhesion theory.
Following on the techniques proposed by Littleton, Zimnik (2000) conducted a series of
clay-steel interface tests using a modified direct shear apparatus. Tests were conducted in a
direct shear box with dimensions of 63mm x 10mm at rate 0.1mm/min. The tests were
conducted to assess the effects of clay mineral type, roughness of steel surface, contact time
and applied normal stress. Two clays prepared from powder: A Speswhite Clay (PI=30)
35
which was determined to have a fine fraction of 79% (<0.002mm by mass) and composed
mainly of the clay mineral Kaolinite. Also a sample of Boom Clay (PI=31) was determined
to have a fine fraction of 71% and composed of quartz, illite, kaolinite and other trace
minerals.
The samples were consolidated first in an odometer then again in the direct shear apparatus.
In this fashion all samples were considered to be normally consolidated prior to testing.
Tests were typically carried out under consolidated undrained conditions in accordance with
the procedures outlined in ASTM D-3080. The normal loads were varied at least up to the
loads existing at the tunnel face and in the mixing chamber of the TBM. Various steel plates
with different roughness coefficents were prepared for the testing by varying the intensity of
sparkling at the surface which creates an isotropic roughness (Zimnik, 2000). It was found
that the adhesive shear strength increases linearly when it is plotted as a function of normal
stress between 0 and 500kPa.
The adhesive strength of both clays was found to vary with slight variation in the roughness
of the plates as can be seen on Figure 16. The effect is more noticeable at higher confining
pressures. According to Zimnik, this is due to the fact that increasing the normal stress and
with increasing roughness more internal deformation takes place, causing strain hardening.
At this point shearing will be more likely occur within the sample rather than across the
interface with the steel. For both clays a critical roughness between 2.4 and 4.7μm was
observed. The Speswhite also showed higher adhesive strength values than did the Boom
clay likely due to the effects of the different mineral constituents.
36
Figure 16 - Influence of Roughness in Direct Shear Adhesion Tests with Contact Time of 1-Hour (Zimnik, 2000)
The influence of contact time is presented in a similar manner in Figure 17. The lowest
roughness steel plate was chosen for these tests to ensure that shear was occurring at the
contact and not within the clay samples. Contact times included consolidation time in the
direct shear box. Generally it was observed that an increase in adhesive shear strength was
found with an increase in contact time particularly at higher normal stresses.
37
Figure 17 - Influence of Contact Time in Direct Shear Adhesion Tests, Steel plate with roughness of 0.2μm (Zimnik, 2000)
The moisture content of the samples were measured before and after each test to compare
soil consistencies. Before and after shearing the water content of each sample was above the
plastic limit. After the test the consistency index for each clay increased which would lead to
an increase in the adherence potential. At higher normal stresses this feature is more
pronounced.
38
In a similar series of tests Kooistra (1998) expanded the clay sample pool to investigate more
thoroughly the contributing factors to adhesive shear strength. A commercial potters clay
(K122); a kaolinite (China clay); the drilling mudnamed bentonite, but actually consisting of
the clay mineral sepiolite (instead of montmorillonite); a Boom clay, a type in which
tunneling and underground construction has occurred in Belgium and which will be
excavated in the Westerschelde tunneling project; Kedichem clay, which has recently been
excavated during tunneling near Heinenoord (Rotterdam); Eem clay, a clay which will be
excavated in the Noord-Zuid tunnel project in Amsterdam. On the samples dry volumetric
weight, water content, grain size distribution by wet sieving, Atterberg limits (liquid and
plastic limit) and the Cation Exchange Capacity (CEC) using the mrthylene blue spot
method were determined.
Samples of the normally consolidated potter’s clay (K122, PI=33,A=0.62, Ic=0.73) and over
consolidated Boom Clay (PI=50, A-0.93, Ic=1.06) and Kedichem clay (PI=26, Ic=0.35)
were tested in the shear box 100x100x12mm modified for adhesion testing. The clays were
sheared at a low rate of 0.5mm/min over a partially rusted metal surface. The metal surface
was chosen to increase the real contact area with the clays and to mimic TBM cutting tools.
The tests were carried out under consolidated undrained conditions, following the
procedures outlined in ASTM D-3080-90. The normal loads were carried up to 500kPa “a
range relevant to the pressures existing in the mixing chamber of the tunnel boring machine
of the second Heinenoord tunnel.”
The results of the shear box tests are shown in Figure 18. For the normally consolidated
clay at its natural moisture content the adhesive shear strength was constant at 9kPa for low
39
normal stresses, above 25kPa normal stress the adhesive shear strength increased linearly.
For the overconsolidated clays at natural water content and low normal stress the adhesion
was very low and only adhesive friction appeared to contribute. At higher normal stresses
(between 70 and 100kPa) the apparent adhesion was higher and reached 30kPa for the
Kedichem clay and 80kPa for the Boom clay.
Figure 18 - Results of Modified Shear Box Tests (from Kooistra 1998)
Further testing to evaluate the effect of the moisture content was performed on the normally
consolidated potters clay (K122). Shear box adhesion and traditional cohesion tests were
40
carried out in the same manner at low normal stress between 25 and 55kPa. In this study the
peak cohesion was found closer to the plastic limit than the liquid limit. Also from the
results, according to Kooistra: “It can be seen that for this clay cohesion is higher than
adhesion for all water contents and that cohesion exponentially decreases with water
content”. It was suspected by Kooistra that the results were indicative of the Kaolin type
clay tested and that values of adhesion that exceed the cohesive shear strength of a clay
sample at a particular moisture content may be found with the testing of clays with higher
activity values.
3.3 On-Going Research
Another test developed for the purpose of quantifying the stickiness of clays is the cone pull
out test apparatus (Feinendegen et al, 2010). For the test the clay is compacted into a
standard proctor mold and a cone shaped hole is predrilled into the top of the sample. A
cone which fits the size and shape of the hole is inserted into the cavity and loaded for a
period of 10 minutes with an applied pressure between 3.8 and 189 kPa. The load is the
removed and the cone is pulled out at a velocity of 5mm/ min as the tensile force and
displacement are recorded over time. Several different cones with inclinations ranging from
10˚ to 73˚ have been developed for the test as shown in Figure 19.
41
Figure 19 - Cone Pull Out Testing Apparatus, developed by InProTunnel Working Group (from Feinendegen et al, 2010)
In some preliminary testing performed by Spagnoli (2010) he found that the maximum
tensile stress for the overconsolidated Westerwald clay (Ic=0.7) was generated at a cone
displacement of about 2mm for all cone inclinations. For the apparatus with cone inclination
between 30 and 45˚ the maximum tensile stress on the cone was above 20kN/m² and
approached zero at about 5mm of displacement. For cone inclinations between 55 and 75˚ a
maximum tensile stress of about 16.5 kN/m² was generated and tensile forces continued to
be measured at 10mm of displacement or more. Further testing was performed to test the
effect of the water content of a soil to the pull out resistance. Soil consistencies between 0.2
and 0.85 were tested. For low consistencies below 0.6 tensile stresses were measured over a
relatively large cone displacement of 20 to 25mm and reached a maximum tensile stress of
about 11kN/m². For consistencies above 0.6 the curves of tensile stress Vs. displacement
becomes much steeper and the maximum stress recorded for a consistency of 0.85 was
24.5kN/m². Results of the tests are summarized in Table 3.
42
Table 3 - Cone Pull Out Test Results - Tensile Strength Vs. Displacement for a cone inclination of 58 degrees and an overconsolidated clay
Consistency Maximum
Tensile
Strength
Displacement
at Max
Tensile
Stress
Maximum
Displacement
of nonzero
Tensile
Stress
Total Pull
Energy
Total
Adherence
0.2 2kN/m² 8mm 24mm 28kNmm/m² 290 g/m²
0.4 8kN/m² 7mm 22mm 102kN
mm/m²
770 g/m²
0.55 11kN/m² 4mm 14.5mm 88mm/m² 600 g/m²
0.7 16.5kN/m² 2mm 10mm 63mm/m² 530 g/m²
0.85 24.5kN/m² 1mm 5mm 25mm/m² 70 g/m²
(data from Spagnoli, 2010)
A new classification scheme was developed for assess the potential stickiness of clays based
on the relative consistency using the cone pull out device. The proposed system is shown
graphically in Figure 20. A good correlation was found between the total pull energy
(integral of the Consistency Vs. Pull Energy curve) and the Adherence which is determined
by weighing the amount of clay that is stuck to the cone apparatus once it has been extracted
from the sample. For the study adherence values less than 150 g/m² were considered to
indicate a low clogging potential and values measured above 300 g/m² indicated a high
clogging potential. The highest pull energy and adherence where found at a relative
consistency of 40 to 60% and the adherence vales remain in the zone of high clogging
potential over a consistency range of 25 to 75%.
43
13) Westerwald Clay, 14) London Clay, 15) Boom Clay, 16) Smectite Clay
Figure 20 - Proposed adherence Classification System based on the Cpone Pull Out Test (from Spagnoli, 2010)
44
4 Industry Experience and Case Studies
The first step in dealing with sticky clays along a tunnel alignment is to identify the extent of
the potential issue in the preliminary design phases. A desktop study should be performed at
the earliest stages of developing the project concepts in order to obtain geological
information to identify the likelihood sticky clay deposits. This information could be
particularly useful as part of the trade-off study of choosing potential methods (trenchless
Vs. cut and cover) and horizontal and vertical alignments. Next, during the preliminary
design stages investigation techniques, field observations and simple laboratory index testing
can be used to identify the potential for clogging to be an issue. For advanced studies a
mineralogical analysis to identify the relative percentages of different minerals such as
Kaolinite, Illite and Montmorillonite within the alignment can be performed.
The Thessaloniki Metropolitan Railway project is comprised of two separate 6 meter
diameter tunnels over an 8 kilometer stretch in Greece. The tunnels will be excavated with
the use of two EPBM machines. The geology consists of gneiss bedrock overlain by
Miocene to lower Pliocene stiff to hard clays and silty clays and Quarternary alluvial gravels,
sands and clay deposits. The tunnel alignment encounters the “red” clay and silty clay
deposit mainly. The consistency of the clay deposits along over 50% of the alignment
consists of stiff to hard clays. The potential clogging risks to the TBM were evaluated based
on the Thewes method (Figure 21) discussed previously and a system used by Geodata-
Torino (Figure 22). For the Athens Metro Line 3 extension project the potential for sticky
behavior was based on a relationship between the ratio of natural moisture content to plastic
limit and the plasticity index. Using all of the data from the Thessaloniki Metro the Thewes
45
method indicates a medium to high (72% of data points) TBM clogging potential and the
Geodata-Torino method indicates a low (70% of data points) clogging potential.
Figure 21 - Clogging Risk of Thessaloniki Metro based on the Thewes method (from Marinos, 2007)
Figure 22 - Potential for Sticky Behavior of Cohesive Soils of Thessaloniki Metro based on the Geodata-Torino method (from Marinos, 2007)
46
The Beacon Hill Project in Seattle Washington, was a transit tunnel excavated in Glacial
Till from 2005 through 2009 using an EPBM. As part of the design adhesion limit tests
along with Atterberg limits and natural moisture content testing were performed. All of the
natural water content testing placed the material below the adhesion limit indicating the clays
were not prone to sticking. Although not considered at the time, computing the consistency
and plotting it against the plasticity index using the Thewes method indicated a potential for
some of the soils to include sticky clays. Ultimately the tunnel was specified to include up to
25% of potentially sticking material due largely to the clients past experience with similar
projects. After construction commenced the adhesion of clay was observed in the cutter
head, screw conveyor and muck conveyor.
After identifying the clay bearing units within a planned tunnel drive and the magnitude of
the stickiness of the clay, TBM manufactures can use this information to optimize some of
the components on a new or refurbished tunnel boring machine. Some of the methods that
have been shown to work well in the past include (Thewes, 2005); spreading out cutting
tools to create larger soil chips which reduces adhesive surface to volume ratio of spoils;
enlarged passages for soil transport from tunnel face to the screw conveyor or slurry line;
increased agitation in areas prone to settlement which prevents agglomeration; use of open
“spoke like” cutting wheels which decreases the amount of metal surface in contact with the
excavation face; smooth out sharp angles within the excavation chamber and; include an
independent active center to the cutting wheel which can be turned at a higher rotational
speed. When issues arise during TBM advancement either planned or unplanned the
contractor can; reduce the advancement rate; replace worn tools and surfaces; maximize
47
suspension flow rate; flush the excavation chamber; operate under partial air support and;
add chemical additives to the slurry.
For the Subway Essen Lot 34 completed in Germany in 1990 (Wayss, 1995) a 8.3m (27ft)
diameter slurry TBM was a used. The slurry shielded TBM was chosen to limit surface
settlements in some of the soft cohesive soils. To handle potential clogging issues in the stiff
cohesive soils conditioning agents injected in the slurry along with the first ever use of an
independently spinning center cutter. A photo of the independent center cutterhead is
shown on Figure 23. The center cutter acts as its own separate TBM running in EPB mode
and discharging into the working chamber.
Figure 23 - Independent Cutter Head Used in TBM on Subway Essen Lot 34 Project (from Waays, 1995)
The Westerschelde Tunnel in Netherlands was considered a landmark project in the
evolution of the TBM machine to handle sticking clays in a weak rock formation (Sagar,
1999). As part of the design a geotechnical evaluation was performed specifically to assess
the clogging potential of the alignment soils which were identified in over two thirds of
48
tunnel drive. Two Herrenknect mixshield TBMs were used to complete the transit tunnel in
a Tertiary aged, overconsolidated, highly plastic (illitic-montmorillonitic) Boom clay. The
machines included optimized cutting wheels, excavation chambers and suction inlet areas
and a sophisticated flushing system that used a data acquisition system to optimize slurry
concentrations and recirculation rates. Specific features of the TBMs were open spoked
cutterheads with streamlined cutting arms and soft ground cutting tools, individual feed and
slurry lines, excavation chambers lined with steel sheets to avoid clogging prone angles and
rotary ( as opposed to jaw) crushers equipped with agitators inside the inlet suction area.
Additives are commonly used, particularly in slurry faced TBM drives to reduce clay
adhesion at the face and in the return line. As previously explained the diffuse double layer
between clay particles within a clayey material is made up of both absorbed water and free
water that contains salt molecules (cations). Because clay particles are negatively charged on
their surfaces but contain positively charge water layers clay molecules include both
attractive and repulsive forces towards one another. Anti-clay additives serve to increase the
electrostatic repulsive force between clay particles by adding additional anions to the diffuse
double layers which separate the particles. Since cohesion is related and thought to be a
direct result of the attractive forces created by the shared water layers, increasing the
repulsive force between clay particles will decrease the influence of cohesion on the shear
strength of the soils.
The Silicon Valley Rapid Transit (SVRT) is an extension onto the existing Bay Area Rapid
Transit (BART) system included five miles of twin bore tunneling in San Jose California
(Ball, 2009). The preferred tunneling method was to use an Earth Pressure Balance Machine
49
(EPBM) through the clayey soils. As part of the design a sample of high plasticity clay with
trace sand was retrieved from one of the sonic borings. The samples were supplied to the
laboratory at BASF chemical company for testing of the effectiveness of different soil
conditioners. The soil was divided into smaller samples and different ratios of water, foam
and anit-clay agents were added to the samples and blended with a metallic mixing paddle.
The amount of clay adhering to the paddle along with observations on the way in which the
clay covered the windows within the paddle surface and the amount of work required to spin
the paddle were recorded (Ball, 2009).
The preferred ratio of water and the different conditioning agents were determined prior to
the commencement of TBM excavation. For this project a mixture of additional water, anti-
clay admixtures and foam was chosen. Foam which when combined with air expands when
agitated further increasing the clay dispersion and thereby reducing the shear stress needed
to break the bonds between clay particles. From this testing it was observed that a mixture of
7.5% by weight of water, 1.5% of Rheosoil 211 (BASF Inc.) a water soluble deflocculating
agent and 30% foaming agent for bulking the soil mix to cut down on torque was optimal at
reducing adhesive strength and total adhesion to the mixing paddle.
The Bay Division Pipelines Reliability Upgrade Project is an upgrade to the existing water
system which serves residential customers in the city of San Francisco (Ericson, 2005). One
component is the Bay Division Pipeline a 21 mile long pipeline that includes a tunnel (Bay
Tunnel) under the San Francisco Bay. The Bay Tunnel will consist of a 108 inch internal
diameter pipeline extending 5 miles under the San Francisco Bay, adjacent marshlands and
Salt Ponds. Due to environmental concerns only a launching and receiving shaft will be
50
constructed and the entire tunnel length will need to be completed in one drive. The tunnel
depth ranges between 70 to 100 feet below the mean surface of Sand Francisco Bay. The
tunnel is to be constructed as a two pass system and the initial pass will include the erection
of precast concrete segments immediately behind the pressurized face TBM. Geologic
conditions include marine deposits including younger (soft) and older (stiff to hard) silty
clays, alluvial deposits including beds of medium stiff to hard silty clays and highly weathered
sedimentary and metamorphic rocks.
A EPBM was selected as the most appropriate machine for the ground conditions due to the
high percentage of cohesive soils. The ability to inject foam (foaming agent and air) into the
working chamber to stabilize the ground and reduce the torque required to cut the ground
thereby reducing the cutter wear was an important factor to choosing TBM types. Polymers
and dispersants added to the foam water mix will be used to reduce the potential for the
highly plastic soils to stick to the metal cutter head and screw conveyor. Another goal of
optimizing ground conditioner application is to reduce cutter head torque and abrasion
which is particularly important in this long drive with no intermediate access. Frequent
inspections of the cutting tools will be implemented particularly in areas of high likelihood of
wear.
51
5 Description of Testing Program
5.1 Previous Laboratory Testing Programs
Previous studies related to interface testing between clay and steel surfaces have been
performed primarily with the use of a modified direct shear device or more advanced testing
equipment designed specifically for testing certain parameters. The direct shear apparatus,
utilized by Litttlejohn (1976) for clay-steel interface testing, is easy to operate but it has a
number of disadvantages, most important of which is that shearing stresses and strains are
not uniformly distributed over the contact surface which causes progressive failure beginning
at the ends of the soil specimen. Additionally, in order to determine the residual strengths of
clays the direct shear device has to be reversed several times before the failure surface is fully
established. Following on the techniques proposed by Littleton, Zimnik (2000) conducted a
series of clay-steel interface tests for applications specific to tunneling using a modified
direct shear apparatus. Zimnik chose a range of confining pressures and steel surface
roughness coefficients similar to what had been observed in some recent TBM drives. For
both clay samples tested a critical roughness coefficient between 2.4 and 4.7μm was
observed, above which shearing was likely to occur not at the interface, but within the
sample itself.
Yoshimi (1981) created a custom ring shear device in order to perform interface testing
between common construction materials and different sands. The apparatus used to stacked
acrylic rings to allow for the tracking of led markers that were embedded within the sample.
Based on led marker movement tracking he determined that shearing strain varied by less
than 10% from the average between the inside and outside radii of the ring sample and that
value reduced considerably after the shear surface had developed. For his tests Yoshimi
52
quantified the R-max value as the largest amplitude if change over the ring surface profile
and he determined the range of R-max values was 3μm (0.003mm) and 510μm (0.51mm) for
construction materials. Other similar type experiments were conducted with R-max values
ranging from 10μm to 20μm (0.01 to 0.02mm) for steel.
Traditionally, ring shear tests are the recommended method for determining the values for
the drained residual strength of clays. The benefits of the ring or torsion shear apparatus are:
the sample width is small in relation to its diameter which provides very low variations in
strain across the width of the sample, the shearing can take place continuously in a single
direction so the machine does not require reversal to develop a failure surface and to
measure residual strengths. For clays, this allows for more complete platy particle
orientation along the shearing plane, and a more accurate measurement of the drained
residual strength than would be achieved in traditional direct shear or triaxial tests (Bishop et
al., 1971). The ring shear test is suited to the relatively rapid determination of drained
residual shear strength because of the short drainage path through the thin specimen, and
the capability of testing one specimen under different normal stresses to quickly obtain a
shear strength envelope.
5.2 Clay Sample
The clay sample used for the laboratory testing program is a white Kaolin “Ball” clay
extracted from the Kentucky portion of the Mississippi Embayment (Mid-Late Tertiary).
The clay was obtained, dried, ground to a powder and supplied by the Old Hickory Clay
Company based out of Mayfield, KY. The clay used for the laboratory testing program has
53
the properties shown in Table 4 which are typical properties based on a rigorous quality
assurance-quality control program and were provided by the manufacturer.
Table 4 - Properties of Kaolin Clay (Old Hickory Clay Company) Property Unit Average Value (Range)
Particle size,
%Finer than
75 µm % 100
10 µm % 90
1 µm % 60
0.5 µm % 50
Cation Exchange Capacity Meq/100ml 9.0
Specific Gravity (2.40 – 2.65)
pH 6.0 (4.0 – 8.0)
Silicon Dioxide content % 60.5
Aluminum Dioxide content % 26.5
The primary benefit of using a test sample reconstituted from powder is to avoid any
influence from preexisting consolidation pressures. In addition it makes moisture
conditioning to a certain percentage simpler. Atterberg limits of the sample were estimated
based independent testing by the author. Five separate tests were conducted to determine
the plastic and liquid limit and the corresponding plasticity index in accordance with ASTM
D4318. The estimate of the “stickiness index” is based on the original test method proposed
by Atterberg and is an estimate taken for comparison purposes. Results of atterberg limit
testing are presented in the Section 6.
54
5.3 Consolidation Testing
Prior to conducting the modified ring shear tests the consolidation parameters of the
remolded specimens were estimated by conducting several consolidation tests in accordance
with ASTM D2435. The consolidation testing apparatus consisted of the consolidation
device which includes the sample ring, porous stones, filter paper, water reservoir and
loading plate in addition to the dial gauge and sample preparation tools. The consolidation
testing device used was made by Wykham-Ferrace and is shown as an image in Figure 24.
Figure 24 - Photograph of 1-Dimensional Wykham Ferrace Consolidometer
The sample was wetted to moisture content just above the liquid limit and remolded into
the loading chamber. The weight of the dry and wet sample was measured along with the
precise dimensions of the sample chamber in order to calculate the density of the sample.
The sample was placed into the sample chamber and the vertical deformation gage set to
zero. Loads were then applied to the sample using the weight counterbalance system of 1:10
ratio. The loading schedule included applied pressures to the sample of 0.25, 0.5, 1.0 and
2.0tsf. A stopwatch was started at the same moment loading was applied in order to take
55
accurate measurements at time intervals of less than 30 minutes. Deformation readings were
taken at intervals of increasing duration throughout the consolidation phase in order to
define the deformation vs. log time curve to appropriate detail.
ASTM D 6467-99 provides standardized guidance for sample consolidation for drained ring
shear testing of cohesive soils based on the results from the consolidation tests. Results of 1-
D consolidation testing are presented in Section 6.
5.4 Bromhead Ring Shear Apparatus
The testing program was conducted primarily with the use of the Bromhead ring shear
apparatus, WF25850 (Bromhead, 1979) built by Wykeham Farrance Engineering Ltd. The
device used for the testing is shown in images in Figure 25. The manual for the ring shear
apparatus is included as an Appendix A to this report.
Figure 25 - Photographs of Wykham Ferrace Ring Shear Apparatus
56
To use this apparatus a ring shaped soil specimen 5mm (0.197in) thick with an inside
diameter of 70mm (2.756in) and an outside diameter of 100mm (3.937in) is molded into
place in the sample chamber. The sample is then confined between two (top and bottom)
concentric rings. The rings that are supplied with the testing apparatus are made of a porous
bronze material that has been rigged on the surface which is in contact with the sample. In
the traditional test the sample is meant to shear not at the interface with the ring but within
the sample itself. Confining pressure is provided by a counter balance system with a 10:1
ratio of applied load to weight added. Metal weights are also provided that relate to standard
pressure increment. A rotation is imparted to the base plate and attached lower platen by
means of a variable speed motor and gearbox driving through a worm drive. Measurements
of sample vertical displacement are made by means of a sensitive dial gage bearing on the
top of the load hanger. Torque transmitted through the sample is measured by a set of twin
load measuring proving rings located on either side (North-South) of the sample chamber
and bearing on a cross arm attached to the top plate and upper platen.
5.5 Modified Ring Shear Interface Test
The main phase of the testing program is a series of consolidated undrained or “Quick” ring
shear tests which should most accurately simulate conditions at the soil-cutter head contact
in a TBM tunnel. Due to the rotational speed at which the cutter head moves against the soil
when operational it is unlikely that a drained state is reached in a typical construction
scenario. The primary purpose of the testing program is to evaluate how the adhesive shear
strength of clays to metal surfaces changes and is related to:
Clay consistency,
Micro-Roughness of the steel surface in contact with the clay,
57
Normal force, and over consolidation ratio of the clay specimen.
In order to modify the Bromhead Ring Shear Apparatus several steel rings with different
levels of micro-roughness were machined to serve as a replacement for the top and bottom
brass rings that are available with the ring shear device. For the top ring two separate steel
rings were machined from a solid steel disk of multipurpose (low carbon, industrial) stainless
steel. The solid steel disk(s) were obtained from McMaster-Carr industrial supplier. The
specifications of the steel disks and the machined top and bottom rings are provided in
Appendix B. of this report. From the steel disks, solid steel rings with the same dimensions
as the top wing provided with the ring shear device were machine cut and drilled so the rings
could be secured to the top plate of the Bromhead Ring Shear device. The dimensions and
roughness details of the modified stainless steel top rings are shown in Figure 26.
Photographs of the two rings used for the interface testing are shown in Figure 27.
The two different rings with R-max values of 2µm (0.002mm) and 20µm (0.02mm) were
used to conduct the interface testing. The roughness coefficents were chosen because they
represent a range of roughness coefficients for steel interface testing conducted in the past
(Littlejohn, 76, Yoshimi, 81, Kooistra, 98, Zimnick, 00). Every attempt was made to
maintain the integrity of throughout the testing program so as to change the roughness over
time.
58
Figure 26 - Schematic of Top Steel Rings
59
Figure 27 - Photographs of Top Stainless Steel Rings
In addition to the top ring modifications, it was learned from trial and error early in the
testing program that the bottom or base ring supplied with the Bromhead apparatus had to
be replaced with a stainless steel machined ring as well. The details as to how this conclusion
was drawn are presented in the results section of this report. Similar to the top rings, a
bottom ring with an average surface roughness coefficient of 250µm (0.25mm) was
manufactured and secured to the base plate of the ring shear apparatus. A schematic of the
bottom or base ring can also be found in Appendix B of this report.
60
5.5.1 Modified Ring shear Assembly Procedures:
The procedures for assemblage of the ring shear device (assuming the primary assembly of
the motor, gear box, and worm drive has already taken place) is performed in the following
steps:
1. Remove the sample chamber and the torque arm assembly from the sample bath by
removing the locking screws and using the lifting screws to move
2. Remove the torque arm assembly from the sample chamber using the lifting nuts.
3. Remove the bottom brass ring from the chamber by unscrewing the four screws.
Replace the ring with the steel ridged and roughed bottom ring using the same
screws.
4. Remove the top ring brass ring from the torque arm assembly in the same manner.
Replace the ring with one of the top steel ring with known roughness
5. Reassemble the sample chamber and torque arm assembly and replace in bath by
center pin. Reattach with clamping screws.
5.5.2 Sample Preparation Procedures:
The sample preparation includes reconstituting the clay by adding and thoroughly mixing
water with the clay powder and molding the reconstituted clay sample into the ring shear
sample chamber. These activities are performed following these steps:
1. Measure the mass of a metal dish. After, place enough clay powder in the dish to fill
the ring sample chamber once sample is hydrated.
2. Measure the mass of the metal dish and the sample combined. Calculate the amount
of distilled water to add to the sample using the following formula (assuming pre-test
61
moisture content of 70%) and add the water in a controlled manor so as not to cause
splashing.
1
3. Thoroughly mix the powder clay sample with the water using a rounded end spatula
capable of maintaining contact with the sides of the bowl. Mixing will involve
circular motions with the spatula as well as downward (squeezing). The goal is to
expose all of the clay mineral surfaces to the water. Mixing should continue until the
consistency of the clay is homogeneous at which point it should behave similar to a
wet putty.
4. Make sure the ring shear device is level
5. Moisten the bottom ring of the apparatus enough to completely cover the surface
with a film of water but not so much that it will dramatically affect the moisture
content of the sample
6. Carefully place the hydrated clay in the ring chamber on top of the bottom ring. First
using the small rounded end spatula place the clay in clumps or balls around the
perimeter and in the corners of the ring chamber. This will help to avoid any voids
from forming in the sample.
7. After the bottom ring is completely covered with sample and there is good contact
everywhere on the ring, begin placing additional hydrated clay sample in the chamber
until the top collar of the chamber is reached. Use the flat ended spatula to work the
clay sample into the chamber and to strike off excess sample above the collar so the
top of the molded clay sample is even with the top collar.
62
8. Wet the top ring that is attached to the torque arm similar to the how the bottom
ring was wetted. Carefully place the torque arm over the sample, centering it on the
centering pin. Do not drop the torque arm onto the sample.
9. Move the loading yoke so the loading bolt is centered on the receiving plate of the
torque arm. Turn the loading bolt as necessary to achieve good contact.
10. Swing the vertical displacement gage and tighten its holding bolts so it is centered
over the loading bolt and has good vertical contact with the top center of the bolt.
Tighten the holding bolts so the gage won’t move during the test.
11. Submerge the sample chamber by filling the water bath with distilled water.
12. Shortly after submerging the sample, apply a seating pressure to the sample to
prevent swelling. The seating pressure can be applied using the 0.25tsf (calibrated for
1:10 load arm) weight.
13. Load the sample according to the loading schedule to allow for complete and
homogeneous consolidation at each of the given pressures. Do not overload the
sample at any given time step before the complete consolidation has been reached
from the previous time step.
14. If conducting an Over-consolidated test remove loads in accordance with the correct
time sequence and allow enough time for complete swelling to occur at the given
load.
15. Record vertical displacements at increments for the consolidation and swelling
phase(s).
63
5.5.3 Interface Ring Shear Testing Procedures:
Once the ring shear device has been modified with the stainless steel rings (Section 5.5.2),
interface testing of the consolidated clay sample is conducted in the same manner as a
normal undrained shear strength test in the ring shear apparatus. The procedures for testing
are as follows:
1. Measure and record the mass of a clean, dry metal dish and set it aside until after the
shearing phase is complete.
2. Prior to engaging the ring shear drive motor make sure the sample has been prepared
and is fully consolidated (normally or overly).
3. Swing the proving ring turret (North or South) into position by loosening the locking
nuts at the base of the turrets. The proving ring assembly is in correct position when
the bearing rods are perpendicular with the torque arm loading plate facing the ring
turret.
4. Unscrew the bearing rod to extend it until the rounded end is in intimate contact
with the torque arm loading plate. Be careful not to apply excess force on to the
torque arm as this could lead to some pre-shearing of the clay sample.
5. Repeat steps 2 and 3 for the other proving ring turret.
6. Zero the vertical displacements gage and the two proving ring displacement gages
prior to engaging the drive motor.
7. Adjust the drive motor gear lever setting (A through E) to the correct position and
replace the gear wheels within the gear box manifold to the correct ratio for the
desired ring sample chamber rotational speed. For undrained tests use a ring speed
of at least 0.5mm/min. The conversion of rotational speed to corresponding
translational speed at the center of the ring sample (Mean Diametrical length =
85mm) is as follows:
64
/min 0.742 ./
In order to ensure undrained strength properties use a translational speed of at least
1.5mm/min = 2.0deg/min. (For safety use 3.0deg/min corresponding to gear lever
position of B and a gear ratio of 30:60)
8. Plug in the Ring Shear Device. Confirm power is reaching the drive motor by the
light next to the power button. Make sure the sample bath is topped off and all gages
are still set to zero before turning the device on.
9. Start a timer at the same time the power button is pressed down. Once the power
button is suppressed begin recording observations at each degree or rotation for
vertical displacement and displacement (load) on the proving rings. Also record the
peak displacements (loads) on each of the proving ring assemblies. The specific ring
shear device used is not equipped with a real time data logger. Depending on the
rotational speed chosen in Step 7 it may be necessary to engage the services of an
assistant or a video recording device mounted on a tripod in order to record both
proving ring displacements and the vertical displacement simultaneously.
10. After the test in under way take occasional readings of the timer (minutes and
seconds) just prior to gage readings and record the elapsed time in order to confirm
the rotational speed is as expected.
11. Continue taking measurements until long after the peak shear resistance has been
reached and far enough into shear displacement to confirm the residual interface
shear strength properties. A good rule of thumb is to continue taking measurements
for at least 20 degrees past the peak shear resistance of the sample.
12. After residual shear resistance is confirmed (I.E. additional rotational displacement
does not cause additional load on the proving rings) stop the test by pressing the
65
power button next to the gear box assembly. The ring chamber should stop rotating
and loads on the proving rings should immediately decrease.
13. Disassemble the ring shear device by first rotating the proving ring turrets out of the
way and removing hinge nuts from the sample chamber. Remove the vertical load by
unloading the lever arm, swinging the vertical displacement gage out of the way and
removing the loading yoke from the loading bolt.
14. Carefully lift the sample chamber by the lifting screws and transport the entire
sample chamber to the sink (or another drain).
15. Carefully remove the upper torque arm (and top ring) assembly from the sample
chamber by lifting. Note some additional adhesion will have redeveloped between
the top steel ring and the top of the clay sample in the time since the shearing has
ended. In some cases where large confining pressures were used it may be difficult to
remove the torque arm assembly. In those instances a small amount of torque may
need to be applied to force the sample to release the top ring. In doing so be careful
not to introduce and additional water to the clay sample.
16. Remove the clay sample from the ring shaped sample chamber with the help of a
thin metal spatula and carefully place the clay in the sample dish from Step 1. Again,
be careful not to introduce additional water to the sample or in the dish as this
sample will be the basis for the end of test moisture content measurement.
17. Weigh the sample dish and the “wet” sample and place the dish in an oven of at least
110˚ F for drying of a period of at least 36hrs.
18. Thoroughly clean the sample chamber including the modified steel rings and begin
drying the rings immediately to prevent any deterioration by oxidation from
occurring to the ring face(s). Also clean the Ring shear device water bath container as
66
some of the clay particles will have inevitably settled to the bottom of the tub during
the consolidation phase. Place the assembly in a dry location out of the way until
another test sample is ready to be prepared.
19. After an appropriate time has passed (the oven sample is dry) weigh the sample dish
and the now dry sample, record the mass and calculate the moisture content of the
sample after the test.
67
6 Results of Testing Program
6.1 Atterberg Limits
Atterberg limits are simple tests that were developed to establish the moisture content of
fine grained materials at certain consistencies of the clay-water mixture. Procedures for
determining the plastic limit and liquid limit of a clay sample are established in ASTM
D4318. The liquid limit of the Kaolin sample was estimated using the multipoint technique
(method A) as described by the standard. Four different specimens were prepared at slightly
different moisture contents near the liquid limit. A value of the liquid limit for the sample
was determined based on interpolating between the number of drops of the Casagrande
device required to close a groove in the samples, to estimate the standard 25 blows.
Two separate samples of two masses of clay each were used to estimate the moisture content
at which a thread of clay 1/8” in diameter could no longer be rolled. In addition to these
standard tests the “stick limit” of the clay was estimated by successively adding small
amounts of water to a dry sample until the clay adhered to a steel (as opposed to nickel)
spatula that was passed lightly over the hydrated clays surface. The results of the Atterberg
limit tests are shown in Table 5.
Table 5 - Summary of Atterberg Limit Tests
Atterberg Limit Moisture Content
Range Value
Plastic Limit 25.0% – 25.9% 25.5%
Liquid Limit 53.1% – 59.8% 57.6%
Sticky Limit NA 35.5%
68
Based on the results of the Atterberg limit tests the indices, or moisture content range over
which the clay will behave in a certain manner, can be determined. The plasticity index of the
Kaolin sample was estimated to be 32.1% with a range of 27.2% to 34.8%. The Rieke index
was estimated to be about 10%.
6.2 1-D Consolidation Testing
In order to determine the consolidation properties of the clay sample a 1-D consolidation
test was performed in accordance with ASTM D2435. The standard covers the procedures
for determining the magnitude and rate of consolidation restrained laterally and drained
axially. A sample of the Kaolin clay was prepared from powder at moisture content near its
liquid limit. A loading schedule including the pressures used for the ring shear test; 0.25, 0.5,
1.0 and 2.0tsf was used for the consolidation testing. Measurements taken during the test for
each of the load increments are shown in Appendix C. Plots of deformation Vs. Time for
each of the load increments are shown in Figure 28 through Figure 31.
Figure 28 - Results of 1-D Consolidation Test for Confining Pressure = 0.25tsf
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 1 10 100 1,000 10,000 100,000
Vertical Displacement (in)
Time (mins)
1‐D Consolidation (0.25tsf)
69
Figure 29 - Results of 1-D Consolidation Test for Confining Pressure = 0.5tsf
Figure 30 - Results of 1-D Consolidation Test for Confining Pressure = 1.0tsf
Based on the above plots, the values for time and deformation for each load increment
corresponding to 50% and 100% consolidation using the graphical method (see
interpretation on plots) are shown in Table 6.
0.09
0.10
0.10
0.11
0.11
0.12
0.12
0.13
0.13
0.14
0.14
0 1 10 100 1,000 10,000 100,000
Vertical Displacement (in)
Time (mins)
1‐D Consolidation (0.5 tsf)
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0 1 10 100 1,000 10,000 100,000
Vertical Displacement (in)
Time (mins)
1‐D Consolidation (1.0 tsf)
70
Figure 31 - Results of 1-D Consolidation Test for Confining Pressure = 0.25tsf
Table 6 - Summary of Results from 1-D Consolidation Tests Percent
Consolidation
Property Load =
0.25tsf
Load =
0.5 tsf
Load =
1.0tsf
Load =
2.0tsf
50% Time (min) 55 20 15 15
Deformation (in) 0.050 0.021 0.008 0.003
100% Time (min) 105 100 95 45
Deformation (in) 0.065 0.047 0.014 0.005
From the consolidation data presented above the compression index of the kaolin sample
was estimated based on the void ratio computed at the end of each load increment test
computed based on the following formula (Das, 2007):
Void ratio before test:
Void ratio after test:
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 1 10 100 1,000 10,000 100,000
Vertical Displacement (in)
Time (mins)
1‐D Consolidation (2.0 tsf)
71
and:
where: = Initial Height of Specimen (in)
= Final Height of Specimen (in)
= Height of Specimen Solids (in)
= Mass of Specimen (lbs)
= Cross Sectional Area of Specimen (in²)
= Specific Gravity of Specimen Solids
= Unit Weight of Water (lbs/in³)
A plot showing the final void ratios after each load test along with a linear interpretation of
the change in void ratio Vs. change in pressure is shown in Figure 32.
Figure 32 - Interpretation of Results from 1-D Consolidation Tests
y = ‐0.086x + 0.785
0.600
0.620
0.640
0.660
0.680
0.700
0.720
0.740
0.760
0.780
0.800
0.1 1
Void Ratio
Pressure (tsf)
1‐D Consolidation Test ‐Void Ratio Vs. Log Pressure
72
Based on this analysis a compression index for the Kaolin sample was computed based on
the following calculation (Das, 2007):
. .
.0.164
6.3 Modified Ring Shear (Adhesion) Test
The Bromhead ring shear device utilized for the adhesion testing is not equipped with data
acquisition systems. Due to this, observations of vertical displacement and proving ring
displacements were collected visually and copied onto lab testing sheets similar to the
electronic ones presented in Appendix D. For much of the testing a video recording device
was set up on a tripod over one of the proving rings. After the test was complete the tape
would be reviewed for observations of proving ring displacement. A screen shot from one
of the video files recorded is shown in Figure 33.
Figure 33 - Screenshot of Proving Ring Displacement Gage from Video Recording Device
For this laboratory program, 19 separate consolidated undrained ring shear adhesion tests
were conducted between October 25th 2013 and February 20th 2014. Sixteen of these tests
73
were normally consolidated samples, half of which were tested with the top steel ring that
had a roughness coefficient of 2µm and the other half with the top steel ring that had a
roughness coefficient of 20µm. Confining pressures of 0.25tsf (3.47psi), 0.5tsf (6.94psi),
1.0tsf (13.89psi), and 2.0tsf (27.78psi) were used to conduct the test. For each confining
pressure two consolidated undrained tests were conducted for each steel ring. The other
three tests conducted were overconsolidated undrained tests with overconsolidation ratios
(OCR) of two, four and eight.
The author decided before the laboratory program began that the peak shear stress as well as
the residual shear stress should be determined for each of the tests. This meant that a new
sample of clay had to be prepared, molded into the chamber, consolidated, shear tested and
the chamber disassembled and completely cleaned for every shear test conducted. This
proved to be a very time consuming process and due to the time required to achieve 95%
consolidation (or final swelling), typically only a few normally consolidated tests or only one
over consolidated test could be conducted within a week’s timeframe.
Initially, the laboratory program was scheduled to begin in September 2013 but the first few
tests attempted were failures. The author only planned on replacing the top brass ring that
comes with the Bromhead ring shear device with the low carbon steel rings machined to
different roughness coefficients. For these initially tests the lower brass ring, which has a
much larger roughness coefficient, was used in the test. The brass rings that were shipped
with the device are “porous” (Wykeham Farrance, 1979), most likely to aid in the dissipation
of pore water pressures during consolidation and drained shearing test for which the device
is most widely used. The adhesive suction forces that are developed when an interface
74
adhesion test is conducted between clay and another material are greatly reduced when the
clay is in contact with a porous material. As a result, all of these initially samples failed not at
the interface with machined steel rings or within the clay sample themselves. The samples
instead failed at the interface with the bottom brass, porous ring instead. In fact the samples
maintained the ring chamber shape when the top loading platen was lifted from the bottom
platen. These “failed tests” indicated the existence of the suction force and demonstrated
that the force has a significant impact on the adhesive shear as well as cohesive strength of a
clay specimen.
In order to determine the normal and shear forces from a ring shear test using the
Bromhead ring shear apparatus the following equations, from the manual provided in
Appendix A, are used (Wykeham Farrance, 1979):
Since the sample is narrow in comparison to the diameter the approximation is appropriate.
The torque transmitted through the sample is given by:
23
Since the torque is given by mean load on the proving rings the shear stress is given by:
34
The normal effective stress is given by:
Where: P = Total Load (10x the hanger load)
75
R1 = Inner ring radius
R2 = Outer ring radius
F1=Force on ring 1
L=Distance between proving rings
The above calculations are built into the spreadsheets that contain the ring shear adhesion
testing data presented in Appendix D. All of the samples tested failed at or near the
interface with the top steel ring, based on visual observation. The determination of the
interface shear strength parameters from the testing data was performed similar to the mohr-
columb shear strength parameters. In this way an interface friction angle and an adhesive
(tensile) force was estimated from the test results. The interface friction angle is the slope of
the normal stress Vs. Shear stress line and can be determined from the following equation in
keeping with the Mohr-Columb theory:
∅′
The adhesive force is determined from the extrapolation of the normal Vs. shear stress line
to the intercept with the Y or zero normal force axis (Mohr-Coulumb type material). The
following sections present the results of the interface shear testing based on the variables
considered in the laboratory tests.
6.3.1 Interface Shear Test
For the normally consolidated samples the results of the interface shear tests are presented in
graphical form in Figure 34 and summarized in Table 7. for the tests with the ring of
roughness 2µm and Figure 35 and summarized in Table 8 for the tests with the ring
roughness of 20µm.
76
Figure 34 - Results of Normally Consolidated Ring Shear Interface Tests for Top Ring = 2µm
Table 7 - Summary of Results of Normally Consolidated Ring Shear Interface Tests for Top Ring = 2µm
Date Tested
(Appendix X)
σ
Normal Stress (psi)
τp
Peak Shear Stress (psi)
τr
Residual Shear
Stress (psi)
12/13/2013 3.47 1.57 0.76
12/13/2013 3.47 1.19 0.45
10/25/2013 6.94 3.05 2.68
12/13/2013 6.94 3.42 3.15
10/28/2013 13.89 5.54 5.13
11/1/2013 13.89 4.98 3.62
10/30/2013 27.78 9.34 7.36
12/2/2013 27.78 8.14 6.97
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.000 0.100 0.200 0.300 0.400 0.500 0.600
Shear Stress (tsf)
Displacement (in)
Results with Top Ring R = 2µm
3.47
3.47
6.94
6.94
13.89
13.89
27.78
27.78
Confining Pressure
77
Figure 35 - Results of Normally Consolidated Ring Shear Interface Tests for Top Ring = 20µm
Table 8 - Summary of Results of Normally Consolidated Ring Shear Interface Tests
for Top Ring = 20µm
Date Tested
(Appendix X)
σ
Normal Stress (psi)
τp
Peak Shear Stress (psi)
τr
Residual Shear
Stress (psi)
11/6/2013 3.47 1.93 0.26
11/16/2013 3.47 1.05 0.78
11/15/2013 6.94 4.10 2.28
11/19/2013 6.94 3.70 3.19
11/8/2013 13.89 7.62 6.25
11/20/2013 13.89 6.02 5.14
11/6/2013 27.78 9.72 8.39
11/22/2013 27.78 9.39 8.27
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.000 0.100 0.200 0.300 0.400 0.500 0.600
Shear Stress (tsf)
Displacement (in)
Results with Top Ring R = 20µm
3.47
3.47
6.94
6.94
13.89
13.89
27.78
27.78
Confining
78
There is apparently some scatter in the observations for some of the tests, likely due to
“knocking” created by the machine’s motor system, buildup of frictional forces along the
outside edge of the sample or possibly local inconsistencies with the ring sample due to the
placement process. Generally the curves of Displacement Vs. Shear Stress show a peak
stress value at very low displacements followed by a drop, followed by a leveling off as the
shear surface approaches residual values. The peak value seems to occur at larger
displacements for the 2tsf (27.78psi) confining pressure than for the other, lower confining
pressure tests. In actuality the location of the peak shear stress value likely occurs at
locations further down the displacement curve for increasing confining pressures but the
difference between these locations were too subtle to observe without a data acquisition
system. Comparing the testing observations of the repeat tests in Figures 34 and 35
indicates good agreement which indicates repeatability in the testing results.
6.3.2 Effect of Ring Surface Roughness
As mentioned previously the two steel rings that were utilized as top (interface-shear) rings
in the tests were made of low carbon structural steel and were machined to have specific
roughness coefficients along a profile following the center of the ring rotationally. The first
ring was finished to roughness coefficient of approximately 2µm (0.002mm) and is smooth
to the touch. The second ring was finished to a roughness coefficient of approximately
20µm and has a slightly rough feel when rubbing with fingertips. The difference in the ring
roughness is otherwise difficult to discern except for the slightly different glean of each ring
under a strong light (Figure 27). A comparison of one of the characteristic rotational
displacement Vs. shear stress plots for each of the confining pressures tested and with each
of the top rings is shown in Figure 36.
79
Figure 36 - Comparison of Results of Normally Consolidated Ring Shear Interface Tests for Top Ring = 2 µm & 20µm
At the lower confining pressures of 0.25tsf (3.47psi) and 0.5tsf (6.94psi) there appears to be
little divergence of the peak and residual shear stresses observed in the samples sheared
against the ring with surficial roughness of 2µm and that of 20µm. Comparison of the results
taken from the higher confining pressures, however, indicates a relatively large divergence in
which the interface shear stress of the samples in contact with the ring with surficial
roughness of 20µm were about 10-20% larger for peak and 10-15% larger for residual than
the shear stresses for the sample in contact with lower surficial roughness ring. Comparison
of the results from the confining pressures of 1.0tsf (13.89psi) and 2.0tsf (27.78psi)
demonstrate approximately the same divergence between the two rings.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Shear Stress (tsf)
Displacement (in)
Results with Top Ring R = 2µm & 20µm
3.47
6.94
13.89
27.78
3.47
6.94
13.89
27.78
R = 2µmR = 20µm
80
6.3.3 Effect of Over Consolidation
In addition to the interface ring shear tests conducted on normally consolidated samples
several tests were conducted on over consolidated samples utilizing the ring with the surficial
roughness coefficient of 20µm. Observations recorded from the tests are presented on the
observation logs in Appendix E. A summary of the peak and residual shear stresses for each
of the over consolidation ratios is shown in Table 9. A plot of the rotational displacement
Vs. interface shear stress is presented in Figure 37.
Table 9 - Summary of Results for Overly Consolidated Ring Shear Tests
Date Tested
(Appendix X)
OCR
Over consolidation
Ratio
σ
Normal
Stress (psi)
τp
Peak Shear
Stress (psi)
τr
Residual
Shear Stress
(psi)
11/22/2013 1 27.78 9.39 8.27
2/13/2014 2 13.89 10.36 8.15
2/20/2014 4 6.94 11.17 7.93
2/7/2014 8 3.47 11.98 8.67
The table and plots indicated increasing peak interface shear strength with increasing Over
Consolidation Ratio (OCR) despite the fact that these samples were tested under lower
confining pressures. In fact the peak shear stress measured in the tests increased by 10%,
19% and 28% over the normally consolidated sample for OCRs of 2, 4 and 8 respectively.
The residual strengths however appear to be approaching the same value consistent with a
maximum confining pressure of 2tsf (27.78psi). The plot also indicates that the displacement
81
at which the peak shear stress is measured is less for the samples that are more heavily over
consolidated.
0
2
4
6
8
10
12
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Shear Stress (tsf)
Displacement (in)
Results with Top Ring R = 20µm
OCR=1
OCR=2
OCR=4
OCR=8
82
Figure 37 - Results of Overly Consolidated Tests 6.3.4 Consolidation During Shear Testing
The observations taken from the vertical displacement gage are shown on the lab
observation testing sheets in Appendix D and Appendix E respectively. Plots of the
rotational displacement Vs. vertical displacement (consolidation) for each of the normally
consolidated samples tested are presented in Figure 38 for the samples tested with a ring
roughness of 2µm and Figure 39 for the samples tested with a ring roughness of 20µm.
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Shear Stress (tsf)
Displacement (in)
Results with Top Ring R = 20µm
OCR=1
OCR=2
OCR=4
OCR=8
83
Figure 38 - Consolidation of Samples during Ring Shear for Top Ring = 2µm
Figure 39 - Consolidation of Samples during Ring Shear for Top Ring = 20µm
0.00
0.01
0.01
0.02
0.02
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Vertical Displacement (in)
Displacement (in)
Consolidation with Top Ring R = 2µm
3.47
3.47
6.94
6.94
13.89
13.89
27.78
27.78
0.00
0.01
0.01
0.02
0.02
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Vertical Displacement (in)
Displacement (in)
Consolidation with Top Ring R = 20µm
3.47
3.47
6.94
6.94
13.89
13.89
27.78
27.78
84
All of the samples tested consolidated during shear testing and in general followed the same
pattern in the rotational displacement Vs. Vertical displacement plot. Initially the samples
consolidated at a faster rate which tended to level off as the samples approached residual
shear conditions. Repeat tests show similar results in terms of consolidation during shear
indicating good repeatability of the results. There appears to be some reverse correlation
between the total amount of consolidation experienced by the samples and the confining
pressure which the samples were subject to but this relationship does not always exist.
Plots of the rotational displacement Vs. vertical displacement (consolidation) for each of the
overly consolidated samples (and the normally consolidated comparison sample) tested are
presented in Figure 40.
Figure 40 - Vertical Displacement of Overly Consolidated Samples
‐0.008
‐0.006
‐0.004
‐0.002
0
0.002
0.004
0.006
0.008
0.01
0.012
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Vertical Displacement (in)
Displacement (in)
Results with Top Ring R = 20µm
OCR=1
OCR=2
OCR=4
OCR=8
85
The plot indicates the largest dilation followed by the largest rate and maximum value of
consolidation was observed in the sample initially consolidated at a pressure of 2tsf
(27.78psi) and tested at a confining pressure of 1tsf (13.89psi) with a corresponding OCR
equal to one. The sample with the next highest OCR of two showed a similar but much
more subdued pattern. The sample with the highest OCR equal to 8 that was initially
consolidated at a pressure of 2tsf (27.78psi) and then tested at a confining pressure of 0.25tsf
(3.47psi) demonstrated almost no change in vertical displacement over the interface shear
testing interval.
86
6.3.5 Interface Shear Strength
As discussed in Section 2.3.3, the interfacial shear strength between clay and a solid material
surface can be presented in terms of a Mohr-Coulomb failure type envelope. Plots of the
average Normal Stress Vs. Interface Shear Stress for each of the confining pressures are
shown in Figure 41 for the top ring with a roughness of 2µm and Figure 42 for the top ring
with a roughness of 20µm. Interpretations of a bi-linear Mohr-Coulomb failure envelope are
shown on the plots for both the peak and residual strengths.
Figure 41 - Normal Vs. Shear Stress Test Results for Top Ring Roughness = 2µm
0.0
2.0
4.0
6.0
8.0
10.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Ring R =2µm
Peak Residual
Peak 1
Peak 2
Residual 1
Residual 2
87
Figure 42 - Normal Vs. Shear Stress Test Results for Top Ring Roughness = 20µm
A summary of the interface friction angle and interface adhesion force for the normally
consolidated samples tested with the top ring with a roughness of 2µm is presented in Table
10 and with the top ring with a roughness of 20µm is presented in Table 11.
Table 10 - Interface Shear Strength between Kaolin and Top Steel Ring with Roughness = 2µm
Strength Envelope Friction Angle
(degrees)
Adhesive Force
(psi)
Adhesive Force
(kPa)
Peak 1 22.9 ‐0.17 ‐1.17
Residual 1 22.0 ‐0.36 ‐2.48
Peak 2 12.0 2.75 19.0
Residual 2 7.8 3.34 23.0
Table 11 - Interface Shear Strength between Kaolin and Top Steel Ring with Roughness = 20µm
Strength Envelope Friction Angle
(degrees)
Adhesive Force
(psi)
Adhesive Force
(kPa)
Peak 1 26.8 ‐0.25 ‐1.7
Residual 1 24.5 ‐0.64 ‐4.41
0.0
2.0
4.0
6.0
8.0
10.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Ring R=20µm
Peak Residual
88
Peak 2 12.0 3.80 26.2
Residual 2 10.7 3.07 21.2
A comparison of the two sets of curves for peak strengths is shown on Figure 43 and for
residual strengths on Figure 44.
Figure 43 - Normal Vs. Shear Stress Test Results, Peak Strengths
Figure 44 - Normal Vs. Shear Stress Test Results, Residual Strengths
From the plots, it is obvious that the strength envelopes for the interface shear strength
between the clay and the ring with a roughness of 20µm is larger for both peak and residual
0.0
2.0
4.0
6.0
8.0
10.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Peak
5um 20um
0.0
2.0
4.0
6.0
8.0
10.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Residual
5um 20um
89
strengths. The first portion of the bi-linear strength envelopes demonstrated very small
negative adhesive resistance to shear and most of the shear strength mobilized is due to
frictional forces. The relative divergence of these curves becomes more apparent at higher
confining pressure which is the second part of the bi-linear strength envelope. For the peak
strengths the friction angles for this portion of the envelope are identical and the difference
between the location of the lines is the additional adhesive resistance (difference = 1.05psi)
generated by the ring with the larger roughness coefficient. For the residual strengths the
adhesive force for the ring with the smaller roughness coefficient generated the larger
adhesive resistance (difference = 0.27psi), but the difference is nominal compared to the
values of the respective adhesive strengths.
The location of the normal and shear stress measurements for peak and residual strengths of
the overly consolidated clay samples is shown on Figure 45 and Figure 46 respectively.
Figure 45 - Location of Overly Consolidated Peak Strength Tests Relative to Normally Consolidated Strength Envelope for Top Ring Roughness = 20µm
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Ring R=20µm
Peak 20µm ‐ Peak
OCR=8OCR=4 OCR=2
OCR=1
90
Figure 46 - Location of Overly Consolidated Residual Strength Tests Relative to Normally Consolidated Strength Envelope for Top Ring Roughness = 20µm
From the plots it is obvious that the overly consolidated test results plot above the envelope
for the normally consolidated strengths. The increase becomes greater at larger ratios of over
consolidation which also corresponds to lower normal stresses.
6.3.6 Moisture Content Measurements
The moisture content of the samples was measured both before and after each ring shear
test. A summary of the moisture content testing for the normally consolidated samples is
presented in Table 12. A summary of the moisture content testing for the overly
consolidated samples is presented in Table 13.
It is apparent from the results that all of the samples were initially prepared at moisture
contents above the moisture content that remained after consolidation. The summary of
results indicate that for the normally consolidated samples increasing the confining pressure
reduces the moisture content of the samples for the test. This is a predictable result in which
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0 5 10 15 20 25 30
Shear Stress (psi)
Normal Stress (psi)
Normal Vs. Shear Stress, Ring R=20µm
Residual 20µm ‐ Resid
OCR=8OCR=4 OCR=2 OCR=1
91
the water is being squeezed out of the pore space, similar to what was observed during the 1-
D consolidation test (Section 6.2)
Table 12 - Moisture Contents Before and After Normally Consolidated Shear Testing Confining Pressure
(psi)
Moisture Contents (%)
Before Test After Test - Ave After Test - Range
3.47 72.5 63.1 54.3 – 75.7
6.94 72.5 60.4 55.3 – 67.6
13.89 71.0 58.0 51.5 – 67.8
27.78 71.3 43.0 40.3 – 44.6
Table 13 - Moisture Contents Before and After Overly Consolidated Shear Testing Over Consolidation
Ratio
Confining Pressure
(psi)
Moisture Contents (%)
Before Test After Test
1 27.78 70.0 40.3
2 13.89 70.9 41.0
3 6.94 71.2 45.5
4 3.47 71.9 48.6
For the overly consolidated samples the moisture content of the samples measured after the
tests appear to increase in comparison to the base case sample tested at and OCR equal to
one (normally consolidated). The increases are incremental in comparison to the decrease in
moisture content that was observed from the normally consolidated tests.
92
7 Summary and Conclusions
The use of the tunnel boring machine as a means of mechanically excavating through soils to
build linear underground projects is growing in the US and throughout the world. The ability
of certain clay minerals to adhere or stick to the metal components of a TBM in the
presence of water has the potential to have measurable implications on the schedule and
budget of a particular project.
Shearing of a clay in contact with a metal surface can occur in one of three ways; at the clay-
metal contact, within the clay structure or as a combination of the two. Similar to shearing
strength at clay-clay contact the adhesive shearing strength of clay-metal is dependent on the
normal force applied to the failure plane. If the (cohesive) shear strength of the clay is larger
than the interfacial (adhesive) shear strength of the clay-steel contact than the clay will shear
at the contact with the steel and sticking will not occur. If however the interfacial shear
strength is higher than sticking, and potentially buildup of clay material, will occur.
It has been shown from previous studies and the one conducted for this report, using the
ring shear or torsion device, that the adhesive strength of clays to other surfaces can be
described in terms of the Mohr-Columb failure criteria. Similar to the shear strength
parameters for the clay of friction angle and cohesion, the adhesive shear strength of clay
can be defined in terms of the adhesive friction angle and adhesive tensile force. The
adhesive tensile force is attributed entirely to the suction pressure developed at the clay-
metal interface and can be measure independently from the contact friction angle. Adhesive
friction angle is attributed to the penetration of the clay particles into the asperities of the
93
metal surface and the resulting force of redistribution during shear. In this way as the micro-
roughness of the steel surface, ie. the real contact area, increases so will the adhesive friction
angle.
The previous chapters of this report deal primarily with the physical and chemical processes
of clay-steel adherence and how the variation of certain parameters may affect the relative
magnitude of the phenomena. Clay mineralogy is the primary contributing factor for
adhesion to metal surfaces and the main indicator of susceptibility. The ability of swelling (ie.
sticky) clay minerals to attract and absorb water molecules into their lattice structures creates
the suction force at the clay-metal contact. The potential for attraction of positively charged
water molecules to the negatively charged surfaces of clay minerals increases with increased
surface area of the clay particles. As a result the more “scale-like” clay particles that have
very large surface areas per unit weight will have a higher likelihood of sticking to steel parts.
The activity of a clay is measure of the intensity of the surface charge and can be inferred
using basic laboratory testing techniques. Other more complex methods for determining the
swelling potential of clays include measuring the cation exchange capacity or using x-ray
diffraction to identify clay mineral types.
The behaviors of adhesion and cohesion in colloids (particles < 0.1μm in diameter) is also a
function of the water content and a clay would have to have a water content in its plastic
range for sticking to occur. Relative consistency is a measure of the in-situ water content of
clay within its plastic range relative to its plasticity index. A maximum value of adhesive
tensile strength will occur at a moisture content corresponding to a relative consistency
between zero and unity where the suction pressures are at their highest. Increasing the
94
moisture content beyond this point will cause a drop in suction force as more free water is
available for bonding. Below the water table the consistency of clay is typically dependent
on the level of consolidation of the soil. Under high consolidation pressures the plate like
clay particles will tend to align in sheets normal to the maximum pressure. If high contact
pressures were to form between clay and a metal surface then the real contact area would
increase as the clay particles aligned.
7.1 Ring Shear Device Interface Testing
The modified ring shear apparatus used for the primary data collection for this study is a
relatively simple apparatus to create, provided a ring shear device similar to the Bromhead
type is accessible. To conduct the test both the top and bottom rings will need to be
replaced with the stainless steel or an equivalent non-porous material of the same size and
shape. Otherwise a clay with any magnitude of adhering potential will stick to the non-
porous material and shear at the interface with the porous material. The ring shear device is
well suited to this type of testing because of the relatively even distribution of shearing
strains during the application of the rotational shear forces. The rings used for this study are
comparable to the interface materials used in previous studies in which shearing was
observed both at the interface of clay and steel and below the interface within the clay itself.
The surficial roughness of the rings machined specifically for this testing are comparable
with roughness’s for construction materials used in the soft ground tunneling and within
other related geo-civil industries.
The Kaolin clay used for the interface testing is composed of stacked gibbsite and silica
sheets in a one to one fashion. The Cation Exchange Capacity of the clay sample is 9,
95
according to the distributor, which places it in the center of the range for Kaolin clays
according to data from Grim (1962) Kerr (1951) Lambe & Whitman (1969) and Mitchell
(1976). Previous studies indicate the clay sample would be at the lower end of the
distribution of potential adherence strength for “sticky” clays but, since both Illite and
Montmorillonite clays are less abundant in nature the clay sample used for the testing is
considered to be a good representative for potentially sticky or clogging materials in TBM
applications.
The focus of the testing program was on the undrained shear or “quick” shear of normally
and overly consolidated, saturated clay specimens since that is most representative of the
scenario encountered in the field when TBM clogging issues occur. The atterberg limits
estimated from the testing indicate that the kaolin sample exhibits fairly typical properties for
clay of moderate activity. The average moisture contents of the samples measured after the
tests were complete are presented in Table 14 in terms of the consistency index.
Table 14 - Consistency Index of Clay Samples Tested
Normal Stress
(tsf) OCR
Peak Shear
Stress (psi)
Residual
Shear Stress
(psi)
Average M.C.
(%) Ic
0.25 1 1.5 0.5 63.1% ‐0.17
0.5 1 3.0 2.7 60.4% ‐0.09
1 1 6.8 5.7 58.0% ‐0.01
2 1 9.4 8.3 43.0% 0.45
1 2 10.4 8.2 41.0% 0.52
0.5 4 11.2 7.9 45.5% 0.38
0.25 8 12.0 8.7 48.6% 0.28
96
For comparison the consistency of the “sticky index” is estimated to be about 0.7. All of the
samples associated with the test results presented in this report appeared to have sheared at
or near the contact with the top, low carbon stainless steel ring., which indicates that the
cohesive shear strength within clay samples was higher than the adhesive interfacial shear
strength.
All of the shear stress Vs. displacement plots (Figures 34, 35 & 37) displayed a similar shape
of rapid increase in shear strength up to a peak values, followed by a decrease in shear
strength with decreasing slopes approaching residual values. For a TBM excavation scenario
this means that the highest shear resistance at the interface with the cutting tools will occur
right at the start of cutter head rotation. The commonly observed occurrence of clay
materials forming a cake on the front of the TBM excavation face (Figure 3) means that the
peak adhesive strength of the clays has not been overcome by the rotational force of the
cutter head or the cohesive strength at the clay to clay contacts. For overly consolidated clay
samples the peak strength of the clay increases compared to normally consolidated clays,
making adhesion more difficult to overcome.
A kaolin clay sample was tested with two separate steel rings with different surficial rough
nesses. The finish of the surface of the rings chosen to be similar to a TBM cutter head and
tooling at the start of tunneling operation and at some point during the tunnel drive when
the tools have been subject to a certain level of abrasion on the micro scale. The roughness
of the ring with more asperities could also represent the surficial roughness of new or
refurbished equipment depending on the contractor’s requirements and manufacturer’s
specifications. From the ring shear test results it is clear that both the peak and residual
97
strengths mobilized was about 10-20% higher for the ring with the larger roughness
coefficient, but only when the confining pressure exceeded 1tsf (13.89psi). The increase in
interface shear resistance is likely due to a combination of an increase in frictional adhesive
force caused by the larger confining pressure and an increase in adhesive (tensile) force due
to the decreased moisture content of the sample under the larger confining load.
The normal pressures chosen for the testing were similar to stresses used in other similar
type tests and also were chosen to be indicative of pressures likely to be encountered in a
pressurized face TBM excavation chamber (Zimnick, 2000). It was determined that highly
overly consolidated clay samples exhibited peak interfacial shear strengths as much as 10 to
30% more than normally consolidated samples at the same confining pressures. This trend
may continue as OCRs values are increased since a threshold value was not reached in the
adhesion tests. Exceedance of peak stress, however, occurred at lower rotational
displacements than for the normally consolidated samples indicating a more brittle, as
opposed to plastic, type failure mechanism.
From the plots it appears that while the normally consolidated samples have a trend of
consolidation over displacement, the over consolidated samples initially dilate which is
followed by consolidation as they approach residual strengths. The normally consolidated
samples all experienced additional consolidation during interfacial shear. The overly
consolidated samples on the other hand, dilated during the initial stages of shearing. The
largest magnitude of dilation occurred at lower values of over consolidation. At higher
OCRs very little consolidation occurred during shearing. In the field the increase in volume
of clay materials during shearing may further exacerbate the potential for TBM clogging.
98
The results as they have been presented in the plots in Section 6 illustrate one of the primary
focuses of the testing program. As surficial roughness of “shinny-smooth”, steel equipment
such as brand new cutting gear or a TBM face plate on a TBM cutterhead, increases in
roughness by approximately one order of magnitude the interfacial shear resistance between
the metal and a “sticky clay” formation or clumps of clay from the formation increases as
well. Based on relative comparisons it appears that after some threshold of confining
pressure is reached the level of increase in shear resistance remains about the same.
7.2 Comparison of Results from Previous Studies
Atterberg defined the adhesion limit in addition to the more commonly used plastic and
liquid limits. The adhesion limit is the moisture content at which clay-metal sticking begins
to occur. In this study the adhesive limit for the Kaolin clay sample utilized has been
estimated to be about 35%. The range of moisture content at which clay will adhere to metal
was later termed the Rieke index, which was estimated to be a range in moisture content of
about 22% assuming the clay no longer adheres to metal beyond its liquid limit. A
comparison of the sample used for the ring shear interface testing with other samples used
for interface testing referenced throughout this report is shown in Figure 47.
99
Figure 47 - Comparison of Clay Samples from Various Studies
Tests conducted for the purpose of determining the adhesive tensile force and adhesive
friction angle were performed by Bowden and Taylor as far back as the 1950s. In 1979
Thewes (Section 3.2) developed a testing apparatus to focus on the adhesive tensile strength
of clays in contact with steel. He tested samples from six different clayey formations and
determined that clay mineralogy and consistency were the primary indicators of TBM
clogging potential. He also gathered information from several tunnel construction projects
with varying levels of clogging issues to develop a chart for assessing the clogging potential.
His observations and recommendations regarding clay consistency and the atterberg limits
provide a basis for indicating the likelihood of experiencing potential clogging issues in the
other adhesion studies described in this report.
The Thewes (2005) chart indicates a likelihood for adherence based on a clays plasticity
index. This observed correlation is probably because the plasticity index correlates well with
Kooistra, Sepiolite (Bentonite)
Tokarz
100
the activity level and the likely presence of swelling clay minerals. Comparison of this chart
with the results from other studies and the one done for this report using the ring shear
apparatus, indicate that the recommendations do not exactly conform to the testing results
for adhesive strengths mobilized in drained and undrained clay samples in which higher
adhesive (tensile) resistance strengths were observed at consistency indices between 0.4 and
0.6 (Spagnoli, 2000) and higher adhesive shear resistance strengths were observed at even
lower indices (this report).
Littleton modified a standard shear box to determine the adhesive shear strength parameters
between clay and a smooth low carbon structural steel. The steel surface was polished to a
roughness of about 0.2μm and the clays included a normally consolidated (S1) and an
overconsolidated (S2) high plasticity clay. Adhesive shear strength results were compared
with results from classical shear box tests. Results from Littleton’s undrained tests at a
confining pressure of 360N are summarized in graphical form in Figure 48.
101
Figure 48 - Comparison of Test Results for Consolidated Drained Modified Direct Shear Tests Conducted by Littleton
From the summary plot the over consolidated sample sheared against the metal surface
rather quickly after initiation compared to the normally consolidated sample. This is similar
to the results for the ring shear adhesion test for the overconsolidated samples, presented in
Section 6.3.3. After shearing the over consolidated sample displayed a strain softening
behavior which is likely the result of dilation and the redistribution of the clay particles. The
slightly higher adhesive strength of the normally consolidated sample used by Littleton is
attributed to the higher plasticity index which indicates either a higher fines content or a
greater abundance of swelling clay minerals. For both samples the initial work done to
overcome the adhesive strength of the sample was greater than the work needed to
overcome the cohesive strength of the sample. This would indicate sticking potential and
subsequent build-up of material on metal tools in a TBM excavation scenario. Also from
Littleton’s results the higher the confining pressure the more work is needed to shear along
102
the clay-steel contact. The same results were observed in the ring shear adhesion tests for
confining pressures up to 2tsf (27.8psi). The results indicate that the adherence of clay to
metal surfaces is more dependent on the peak adhesive strength of the clay-metal contact
than the residual. After initial shearing the residual adhesive shear strength was less than the
internal shear strength for both samples used by Littleton which is also true of the sample
used in the ring shear test.
Several working groups working out of the University of Delft (Zimnik and Kooistra)
applied the techniques used by Littleton with the use of a similar modified shear box
apparatus to the conditions of clay-metal interface in a TBM excavation. Consolidated
undrained tests were conducted on normally consolidated and over consolidated clay
samples with shearing at various confining pressures and across steel plates of varying
surficial roughness. The results from these interface shear tests were similar to the results of
the interface ring shear tests. Results for undrained tests for previous studies and this study
are summarized in Figure 49 for comparison.
103
Figure - 49 Summary of Results from Various Authors for Consolidated Drained Modified Direct Shear Tests
The curves from the previous tests indicate that a bi-linear normal Vs. shear stress
relationship exists for overly consolidated samples, but it was observed to also occur from
normally consolidated clay reconstituted from powder for the ring shear interface test. Based
on the previous studies, it was determined that adhesive shear strength increases linearly with
increasing confining pressure up to 500kPa (72.5psi) indicating that this trend is likely to
continue beyond the normal stresses used for this study.
Based on a compilation of test results by Zimnik (2000) a slight increase in adhesive shear
strength was observed particularly with an increasing roughness between 2.4 and 4.7μm.
Increased steel to clay contact time led to an increase in adhesive shear strength, particularly
at higher confining pressures.
A similar result was observed utilizing the two different rings used in the testing for the ring
shear apparatus for this study. An increase of 10-20% in peak shear strengths was estimated
104
for increasing the roughness coefficient between the rings with surficial roughness
coefficients of 2µm and 20µm. The increased adhesive shear strength due to increased
micro-roughness became larger with the higher confining pressures.
Yoshimi performed ring shear adhesion tests on several sands utilizing rings machined to
have different roughness’s. The difference in shearing strain was estimated from measuring
the movement embedded led markers within the sample. The maximum variation of shear
strain across the sample was determined to be less than ten percent. The test indicated the
benefit of using the ring shear device as opposed to the more common direct shear device.
He determined that the coefficient of mobilized friction between the sand and steel surface
was the same for all surfaces prior to initial shear. After shearing the difference in the
coefficient of friction was highly dependent on the steel roughness up to a roughness
coefficient equal to the mean grain size above which there was little increase. The peak and
residual friction coefficients were about equal for steel roughnesses above 20μm (10% of the
mean grain size). This critical value of surficial roughness corresponded to the roughness at
which the samples began to dilate during shearing.
In an effort to add to the growing body of knowledge in regards to clays adhering to TBMs a
testing program utilizing a ring or torsion shear testing apparatus was conducted as part of
this study. One of the objectives of the program was to acquire results from a different type
of test to compare with the adhesive shear strength of clays tested previously under
consolidated undrained conditions using the direct shear apparatus. The results of all of the
testing indicate the material parameters which are most critical for sticking potential and
should be evaluated in an order close to the following:
105
1. Clay Mineralogy – Includes the abundance of swelling (absorbing) clay minerals and
is also measured by the activity of a clay. Can be estimated based on simple Atterberg
limit testing.
2. Moisture Content - Availability of free water and level of saturation of a clay
formation. For a clay to be potentially adhering the moisture content must exceed
the “sticky limit”. If the clay is soft and oversaturated beyond its liquid limit than the
sticking potential reduces to values observed below this sticking limit.
3. Consistency & Consolidation – Includes the normal (overburden) stresses currently
being applied to a clay formation relative to the history of normal stresses applied to
the geology. The most recent information indicates that relative consistency indices
of 0.4 to 0.7 result in the highest level of clay-steel adherence. Additionally larger
values of over consolidation will result in higher adhesive strengths as long as the
moisture content (available water) is not too low.
4. Steel Roughness – Micro-roughness exceeding 2µm (0.002mm) should be evaluated
for their effect (increase) on interfacial shear strength.
The comparison of the results using the different apparatus for normal stress versus
measured sheared stress for the interface of the steel and clay is presented here only to
indicate good agreement in the trend of the envelopes. Due to the differences in testing
procedures, equipment and the complex distribution of stresses with the direct shear
samples careful consideration should be applied before drawing conclusions from these
comparisons. Only after increased numbers of clay-steel adhesion tests have been performed
106
using different materials under various conditions should the results of the two different
methods be compared.
7.3 Implications for TBM Cutter head & Excavation
Soft ground tunneling projects present a seemingly infinite number of technical difficulties
for the engineer and the contractor. Most of the difficulties are due to the ground conditions
that are encountered within a tunnel drive. Today the use of Earth Pressure Balance and
Slurry TBMs is common in underground construction projects. Each of these machines and
a variety of hybrid types are designed to match the geologic conditions and meet the
technical requirements of their intended drive.
Clogging of EPB and slurry TBMs is a common problem, particularly in some urban
locations underlain by problematic geologic formations where tunneling is more prevalent.
Clogging issues typically begin at the excavation face but issues can also develop at the
suction inlet area, within the working chamber, in the screw conveyor and anywhere in the
mucking system. Once adhesion initiates, cohesive forces cause the buildup of material and,
in the case of the cutter head, contact pressures will increase further progressing the issue.
On the cutter head adhesion will typically begin at the center where the rotational speed is
less. The size of a TBM and the cutter head is typically a function of the project
requirements. Just like the machines themselves the cutter head of a TBM can be designed in
a multitude of different ways to meet the anticipated ground conditions.
The actual forces experienced at the contact of the steel cutter head and the geologic
formation or portions of the formation as they are pulled away from the excavation heading
107
are complex and the determination of these forces is beyond the scope of this report. At the
most basic level at the local scale the adhesive force of a clay and a steel surface and by
comparison the occurrence of clay sticking to a steel cutter head surface can be broken down
in terms of a normal force and a shear force. At the global scale the forces imparted to the
excavation face by a TBM include a contact pressure from the TBM thrust mechanisms and
a shear force caused by the rotation of the cutter head by the motor.
Test results and observations related to interfacial shear strength indicate that an
understanding of a clay formation’s mineralogical and consolidation properties, as well as the
previous loading history of the formation, are key to determining the potential for adhering
or clogging of a TBM during construction. At this point, without an understanding of the
complex distribution of shear and normal forces at the cutterhead (for which each TBM
design is unique) we can only summarize the parameters that are likely to result in larger
magnitudes of adherence and therefore and increased likelihood of clogging. To summarize
those properties from the current and previous studies the presence of swelling clay minerals
and consistency indices between 0.3 and 0.7 are likely to have the highest potential for
sticking. Additionally over consolidated clays will have a larger peak adhering strength and
will tend to dilate during shearing which could further exacerbate clogging issues in the
working chamber and muck conveyance system.
The results also indicate there are measures that can be taken during construction which will
most likely reduce the potential for adherence and clogging. It has been found that the
highest rates of advance have been achieved by applying the optimal combination of thrust
and cutter head torque. Lowering the driving force applied by the thrust cylinders will reduce
108
the contact pressures on the face as will lowering the fluid or air pressures in the case of a
supported face, which will reduce the peak and residual shear strengths of the clay material.
The addition of water to the excavation face may not reduce the likelihood of sticking and
may actually increase it, but case studies on similar type projects indicate the addition of
certain cation additives or foams may serve to reduce the attraction forces to water on the
clay mineral surfaces. Finally it is assumed from the shape of the mobilized shear stress
versus displacement curves that the largest magnitudes of interfacial shear strength will occur
at the start of the application of shear force. Therefor the torque applied to the TBM cutter
head should be at its highest value at the start of operation, after which it is assumed the
torsion force can be lowered while still maintaining the same rate of excavation.
Results of the modified ring shear adherence testing indicate that stainless steel surfaces that
are allowed to change from a shinny-smooth finish to a slightly rough feel will increase the
peak adherence strength of the clay-steel interface by approximately 20%. This means that as
the excavation cutter head face plates and tooling begin due to wear due to abrasion the
adhesive shear strength and the potential for sticking will increase. A thorough and dynamic
replacement schedule of excavation tooling or the use of more abrasion resistant metals may
help to extend the time it takes for this increase in interfacial shear resistance to occur. Also,
the author learned from experience that the use of any sort of semi-permeable material will
have much less “attraction” for clay particles. This is probably because suction pressures
developed at the clay-steel interface are allowed to partially dissipate prior to shearing.
109
8 Recommendations
There have been several attempts to create simple models based on case histories to predict
the occurrence of adhering clays based on field observations or simple index tests. While
these models provide useful indicators for identifying potential, they full short of taking into
account all of the primary geologic factors as described at the end of Section 7.3.
The primary forces considered for this study include the active forces generated by the thrust
of the TBM and the torque applied to the spinning cutter head as well as the passive, or
mobilized, forces in the surrounding soil and pore water. The ring shear adhesion test is an
appropriate test for modeling the contact pressure and torque applied to the cutter head.
Some additional modifications to the apparatus could increase the utility of applying the
results to the TBM industry.
In order to more accurately model the action in the excavation face larger steel rings and
possibly solid steel disks could be used. According to the International Tunneling
Association Publication (2000) the wear on TBM cutting tools is dependent on the
susceptibility of the steel to wear as well as the location of the bit on the cutter head, the
average rotational speed and the pressure applied to the excavation face. Another modified
testing apparatus could include the addition of cutting tools to the steel interface material.
Other parameters that warrant investigation of their relative effects on adherence include the
rotational velocity of the steel disk or plate and the effect of changing the contact pressure
(confining pressure) applied during shearing. The next step in the understanding of how to
overcome this prevalent issue would also include the testing of other kinds of materials for
110
use in the TBM excavation and much conveyance equipment. Perhaps other types of
construction grade metals, while not being as strong as low carbon steel, will have overall
benefits to excavation advancement rates due to decreased sticking.
Several TBM modifications have been used in previous tunnel drives including removing
sharp angles, an independent rotating central cutter head and the addition of agitators which
help prevent clay clumps from forming. One method that has been proven to work in
preventing clay agglomeration in the TBM working chamber is the use of additives saturated
with cations. Regardless, it is without question that early identification of the potential for
adhering clays followed by detailed investigation to determine the potential magnitude of the
issue is paramount to the success of the project.
111
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114
Appendix A - Manual For The Bromhead Ring Shear Apparatus
127
Appendix B - Specifications For Modified Steel Testing Rings
3.93”
2.76”
0.25”
#4 Flat Head Machine Screw Holes
Average Surface Roughness 2µm—20µm
Side View
Top View
0.29” (TYP)
Notes:
1) Ring Material is High Grade Steel Alloy
2) Create 3 Rings each with consistent top surface
roughness coefficient
Modified Ring for Steel‐Clay Interface Tes ng
By: Sean Tokarz Date: 6/20/13
3.93”
2.76”
0.25” (Ave)
#4 Flat Head Machine Screw Holes
Rough or Ridged Surface
Side View
Top View
0.29” (TYP)
Notes:
1) Ring Material is High Grade Steel Alloy
2) Top Surface of Ring Roughness to exceed
0.2mm in roughness
Modified Bo om Ring for
Steel‐Clay Interface Tes ng
By: Sean Tokarz Date: 10/1/13
Multipurpose Stainless Steel (Type 304)The most widely used stainless steel, Type 304 has good weldability and formability and maintains corrosion resistance up to 1500° F. Commonly used in chemical and food processing equipment. It may become slightly magnetic when worked and is not heat treatable.
View information on the chemical composition of stainless steel alloys, as well as physical and mechanical properties.
Warning! Hardness and yield strength are not guaranteed and are intended only as a basis for comparison.
Short Rods—Unpolished (Mill) Finish
Hardness: 140-223 Brinell•Yield Strength: 30,000 to 35,000psi
•
Annealed•
Meet ASTM A276 and A479. Rods may be cold finished or hot rolled. Straightness tolerance is not rated. Length tolerance is ±1/16" (unless noted).
3/4" LongDia. Each4" 9208K65 $35.63
Need help finding a product? E-mail or call (630) 833-0300.
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131
Appendix C - 1-D Consolidation Test, Laboratory Observations
Laboratory Test: 1‐D Consolidation Test
Material Type: Kaolin (white)
Date: 10/23/2013
Load: 0.25 tsf (3.47psi)
Dimensions of Sample Calculaiton Solids
Initial height of sample 1.005 in Volume of Sample Solids 1.65 in³
Initial diameter of sample 2 in Height of Sample Solids 0.53 in
Initial Weight of Sample 0.1758 lbs
Initial Moisture Content 10.2 % Test Parameters
Specific Gravity of Solids 2.65 Initial Void Ratio 0.912
Cross Sectional Area of Sample 3.14 in² Final Void Ratio 0.779
Volume of Sample 3.16 in³ Total Deformation 0.070 in
Date Time Elapsed (sec)Elapsed
(min)
Deformation
(in)
Change
(in)Strain Void Ratio
23‐Sep 18:33 6 0.10 0.0184 ‐ ‐ ‐
23‐Sep ‐ 20 0.33 0.0210 0.0026 0.26% 0.907
23‐Sep ‐ 30 0.50 0.0224 0.0040 0.40% 0.904
23‐Sep ‐ 45 0.75 0.0240 0.0056 0.56% 0.901
23‐Sep ‐ 60 1 0.0253 0.0069 0.69% 0.898
23‐Sep 18:35 120 2 0.0292 0.0108 1.07% 0.891
23‐Sep 18:37 240 4 0.0347 0.0163 1.62% 0.881
23‐Sep 18:41 480 8 0.0423 0.0239 2.38% 0.866
23‐Sep 19:27 3240 54 0.0516 0.0332 3.30% 0.848
23‐Sep 19:42 4140 69 0.0648 0.0464 4.62% 0.823
23‐Sep 20:12 5940 99 0.0768 0.0584 5.81% 0.800
23‐Sep 21:12 9540 159 0.0834 0.0650 6.47% 0.788
23‐Sep 22:02 12540 209 0.0840 0.0656 6.53% 0.787
24‐Sep 7:37 2034240 33904 0.0866 0.0682 6.79% 0.782
24‐Sep 18:16 2072580 34543 0.0879 0.0695 6.92% 0.779
Time to % Consolidation t100 105 mins t50 55 min
Deformation to % Consolidation D100 0.0650 inches D50 0.05 in
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 1 10 100 1,000 10,000 100,000
Vertical D
isplacemen
t (in)
Time (mins)
1‐D Consolidation (0.25tsf)
Laboratory Test: 1‐D Consolidation Test
Material Type: Kaolin (white)
Date: 10/24/2013
Load: 0.5 tsf (6.94psi)
Dimensions of Sample Calculaiton Solids
Initial height of sample 1.005 in Volume of Sample Solids 1.65 in³
Initial diameter of sample 2 in Height of Sample Solids 0.53 in
Initial Weight of Sample 0.1758 lbs
Initial Moisture Content 10.2 % Test Parameters
Specific Gravity of Solids 2.65 Initial Void Ratio 0.779
Cross Sectional Area of Sample 3.14 in² Final Void Ratio 0.684
Volume of Sample 3.16 in³ Total Deformation 0.120 in
Date Time Elapsed (sec)Elapsed
(min)
Deformation
(in)
Change
(in)Strain Void Ratio
24‐Sep 18:35 0 0.00 0.0880 ‐ ‐ ‐
24‐Sep ‐ 6 0.10 0.0942 0.0757 7.53% 0.768
24‐Sep ‐ 12 0.20 0.0952 0.0767 7.63% 0.766
24‐Sep ‐ 30 0.50 0.0968 0.0783 7.79% 0.763
24‐Sep ‐ 60 1 0.0986 0.0801 7.97% 0.759
24‐Sep 18:37 120 2 0.1012 0.0827 8.23% 0.754
24‐Sep 18:39 240 4 0.1048 0.0863 8.59% 0.747
24‐Sep 18:43 480 8 0.1099 0.0914 9.09% 0.738
24‐Sep 18:50 900 15 0.1160 0.0975 9.70% 0.726
24‐Sep 19:05 1800 30 0.1236 0.1051 10.46% 0.712
24‐Sep 19:35 3600 60 0.1298 0.1113 11.07% 0.700
24‐Sep 21:34 10740 179 0.1347 0.1162 11.56% 0.691
24‐Sep 22:01 12360 206 0.1353 0.1168 11.62% 0.689
25‐Sep 10:40 2045100 34085 0.1378 0.1193 11.87% 0.685
25‐Sep 16:00 2064300 34405 0.1381 0.1196 11.90% 0.684
25‐Sep 18:20 2072700 34545 0.1384 0.1199 11.93% 0.684
Time to % Consolidation t100 100 mins t50 20 min
Deformation to % Consolidation D100 0.0470 inches D50 0.0205 in
0.09
0.10
0.10
0.11
0.11
0.12
0.12
0.13
0.13
0.14
0.14
0 1 10 100 1,000 10,000 100,000
Vertical D
isplacemen
t (in)
Time (mins)
1‐D Consolidation (0.5 tsf)
Laboratory Test: 1‐D Consolidation Test
Material Type: Kaolin (white)
Date: 10/25/2013
Load: 1.0tsf (13.89psi)
Dimensions of Sample Calculaiton Solids
Initial height of sample 1.005 in Volume of Sample Solids 1.65 in³
Initial diameter of sample 2 in Height of Sample Solids 0.53 in
Initial Weight of Sample 0.1758 lbs
Initial Moisture Content 10.2 % Test Parameters
Specific Gravity of Solids 2.65 Initial Void Ratio 0.912
Cross Sectional Area of Sample 3.14 in² Final Void Ratio 0.655
Volume of Sample 3.16 in³ Total Deformation 0.135 in
Date Time Elapsed (sec)Elapsed
(min)
Deformation
(in)
Change
(in)Strain Void Ratio
25‐Sep 18:52 0 0.00 0.0038 ‐ ‐ ‐
25‐Sep ‐ 6 0.10 0.0043 0.1204 12.0% 0.6826
25‐Sep ‐ 15 0.25 0.0047 0.1208 12.0% 0.6818
25‐Sep ‐ 30 0.50 0.0052 0.1213 12.1% 0.6808
25‐Sep ‐ 60 1 0.0058 0.1219 12.1% 0.6797
25‐Sep 18:54 120 2 0.0069 0.1230 12.2% 0.6776
25‐Sep 18:56 240 4 0.0084 0.1245 12.4% 0.6748
25‐Sep 19:00 480 8 0.0098 0.1259 12.5% 0.6721
25‐Sep 19:07 900 15 0.0127 0.1288 12.8% 0.6666
25‐Sep 19:22 1800 30 0.0140 0.1301 12.9% 0.6641
25‐Sep 19:52 3600 60 0.0166 0.1327 13.2% 0.6592
25‐Sep 20:52 7200 120 0.0178 0.1339 13.3% 0.6569
25‐Sep 21:35 9780 163 0.0179 0.1340 13.3% 0.6567
26‐Sep 8:05 2034780 33913 0.0184 0.1345 13.4% 0.6557
26‐Sep 17:55 2070180 34503 0.0188 0.1349 13.4% 0.6550
Time to % Consolidation t100 95 mins t50 15 min
Deformation to % Consolidation D100 0.0140 inches D50 0.0075 in
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0 1 10 100 1,000 10,000 100,000
Vertical D
isplacemen
t (in)
Time (mins)
1‐D Consolidation (1.0 tsf)
Laboratory Test: 1‐D Consolidation Test
Material Type: Kaolin (white)
Date: 10/26/2013
Load: 2.0tsf (27.78psi)
Dimensions of Sample Calculaiton Solids
Initial height of sample 1.005 in Volume of Sample Solids 1.65 in³
Initial diameter of sample 2 in Height of Sample Solids 0.53 in
Initial Weight of Sample 0.1758 lbs
Initial Moisture Content 10.2 % Test Parameters
Specific Gravity of Solids 2.65 Initial Void Ratio 0.912
Cross Sectional Area of Sample 3.14 in² Final Void Ratio 0.645
Volume of Sample 3.16 in³ Total Deformation 0.140 in
Date Time Elapsed (sec)Elapsed
(min)
Deformation
(in)
Change
(in)Strain Void Ratio
26‐Sep 17:56 0 0.00 0.0009 ‐ ‐ ‐
26‐Sep ‐ 6 0.10 0.0019 0.1359 13.52% 0.6531
26‐Sep ‐ 15 0.25 0.0020 0.1360 13.54% 0.6528
26‐Sep ‐ 30 0.50 0.0022 0.1363 13.56% 0.6524
26‐Sep ‐ 60 1 0.0025 0.1366 13.59% 0.6518
26‐Sep 17:58 120 2 0.0028 0.1368 13.61% 0.6513
26‐Sep 18:00 240 4 0.0033 0.1373 13.66% 0.6504
26‐Sep 18:04 480 8 0.0040 0.1380 13.73% 0.6491
26‐Sep 18:10 840 14 0.0046 0.1386 13.79% 0.6479
26‐Sep 18:27 1860 31 0.0053 0.1394 13.87% 0.6465
26‐Sep 18:56 3600 60 0.0055 0.1395 13.88% 0.6462
26‐Sep 20:05 7740 129 0.0057 0.1398 13.91% 0.6457
26‐Sep 20:35 9540 159 0.0058 0.1398 13.91% 0.6456
26‐Sep 20:50 10440 174 0.0058 0.1398 13.91% 0.6456
27‐Sep 8:13 2038620 33977 0.0060 0.1400 13.93% 0.6452
27‐Sep 12:35 2054340 34239 0.0060 0.1401 13.94% 0.6452
27‐Sep 17:23 2071620 34527 0.0060 0.1400 13.93% 0.6452
Time to % Consolidation t100 45 mins t50 15 min
Deformation to % Consolidation D100 0.0048 inches D50 0.00256 in
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 1 10 100 1,000 10,000 100,000
Vertical D
isplacemen
t (in)
Time (mins)
1‐D Consolidation (2.0 tsf)
136
Appendix D - Normally Consolidated Ring Shear Adhesion Test,
Laboratory Oobservations
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 10/25/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.0 %
After test 60.4 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
16 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 6.94 0.000
17 0.024 20 0.0000 0.0000 0.0065 6.50 0.0063 6.32 6.94 3.052
18 0.048 40 0.0007 0.0007 0.0064 6.35 0.0061 6.05 6.94 2.954
19 0.072 60 0.0010 0.0010 0.0060 6.00 0.0059 5.85 6.94 2.823
20 0.096 80 0.0013 0.0013 0.0060 5.95 0.0059 5.90 6.94 2.823
21 0.120 100 0.0017 0.0017 0.0058 5.83 0.0060 6.00 6.94 2.818
22 0.144 120 0.0018 0.0018 0.0056 5.60 0.0060 6.00 6.94 2.763
23 0.168 140 0.0021 0.0021 0.0054 5.42 0.0060 6.00 6.94 2.720
24 0.192 160 0.0023 0.0023 0.0053 5.30 0.0060 6.00 6.94 2.692
25 0.216 180 0.0027 0.0027 0.0053 5.30 0.0060 5.99 6.94 2.689
26 0.241 200 0.0028 0.0028 0.0053 5.30 0.0060 5.98 6.94 2.687
27 0.265 220 0.0030 0.0030 0.0053 5.30 0.0060 5.97 6.94 2.683
28 0.289 240 0.0032 0.0032 0.0054 5.40 0.0059 5.94 6.94 2.700
29 0.313 260 0.0033 0.0033 0.0055 5.52 0.0059 5.91 6.94 2.723
30 0.337 280 0.0036 0.0036 0.0056 5.63 0.0059 5.91 6.94 2.748
31 0.361 300 0.0038 0.0038 0.0057 5.69 0.0059 5.91 6.94 2.762
32 0.385 320 0.0040 0.0040 0.0057 5.70 0.0060 5.95 6.94 2.775
33 0.409 340 0.0040 0.0040 0.0058 5.80 0.0060 6.03 6.94 2.817
34 0.433 360 0.0043 0.0043 0.0058 5.80 0.0061 6.05 6.94 2.823
35 0.457 380 0.0048 0.0048 0.0058 5.80 0.0061 6.10 6.94 2.835
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 10/28/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.0 %
After test 51.5 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 13.89 0.000
1 0.024 20 0.0000 0.0000 0.0110 11.00 0.0123 12.27 13.89 5.542
2 0.048 40 0.0009 0.0009 0.0110 11.00 0.0123 12.27 13.89 5.542
3 0.072 60 0.0012 0.0012 0.0110 10.99 0.0118 11.83 13.89 5.437
4 0.096 80 0.0019 0.0019 0.0109 10.86 0.0116 11.60 13.89 5.350
5 0.120 100 0.0020 0.0020 0.0108 10.80 0.0114 11.40 13.89 5.288
6 0.144 120 0.0022 0.0022 0.0108 10.80 0.0112 11.20 13.89 5.240
7 0.168 140 0.0028 0.0028 0.0107 10.73 0.0112 11.20 13.89 5.224
8 0.192 160 0.0030 0.0030 0.0107 10.67 0.0111 11.13 13.89 5.193
9 0.216 180 0.0032 0.0032 0.0106 10.64 0.0111 11.07 13.89 5.170
10 0.241 200 0.0035 0.0035 0.0106 10.60 0.0112 11.17 13.89 5.185
11 0.265 220 0.0040 0.0040 0.0106 10.60 0.0112 11.17 13.89 5.185
12 0.289 240 0.0043 0.0043 0.0106 10.57 0.0111 11.12 13.89 5.165
13 0.313 260 0.0045 0.0045 0.0105 10.53 0.0111 11.07 13.89 5.145
14 0.337 280 0.0046 0.0046 0.0105 10.51 0.0111 11.07 13.89 5.140
15 0.361 300 0.0050 0.0050 0.0105 10.47 0.0111 11.07 13.89 5.131
16 0.385 320 0.0051 0.0051 0.0105 10.47 0.0111 11.09 13.89 5.134
17 0.409 340 0.0055 0.0055 0.0105 10.47 0.0111 11.12 13.89 5.142
18 0.433 360 0.0057 0.0057 0.0105 10.47 0.0112 11.21 13.89 5.164
19 0.457 380 0.0059 0.0059 0.0105 10.50 0.0113 11.27 13.89 5.185
20 0.481 400 0.0060 0.0060 0.0105 10.48 0.0112 11.25 13.89 5.175
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 10/30/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 74.0 %
After test 44.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 27.78 0.000
0.5 0.012 0.0000 0.0000 0.0170 17.00 0.0068 6.80 27.78 5.669
1 0.024 20 0.0010 0.0010 0.0189 18.90 0.0203 20.30 27.78 9.337
2 0.048 40 0.0020 0.0020 0.0133 13.30 0.0241 24.10 27.78 8.909
3 0.072 60 0.0025 0.0025 0.0126 12.55 0.0231 23.10 27.78 8.492
4 0.096 80 0.0030 0.0030 0.0119 11.92 0.0224 22.40 27.78 8.175
5 0.120 100 0.0032 0.0032 0.0118 11.75 0.0222 22.15 27.78 8.075
6 0.144 120 0.0038 0.0038 0.0114 11.40 0.0220 22.00 27.78 7.956
7 0.168 140 0.0040 0.0040 0.0113 11.30 0.0220 21.95 27.78 7.920
8 0.192 160 0.0042 0.0042 0.0113 11.25 0.0219 21.88 27.78 7.891
9 0.216 180 0.0049 0.0049 0.0112 11.24 0.0218 21.75 27.78 7.858
10 0.241 200 0.0050 0.0050 0.0113 11.25 0.0216 21.61 27.78 7.827
11 0.265 220 0.0054 0.0054 0.0112 11.20 0.0216 21.62 27.78 7.818
12 0.289 240 0.0058 0.0058 0.0112 11.20 0.0216 21.64 27.78 7.822
13 0.313 260 0.0060 0.0060 0.0112 11.18 0.0217 21.70 27.78 7.832
14 0.337 280 0.0061 0.0061 0.0111 11.12 0.0217 21.70 27.78 7.818
15 0.361 300 0.0064 0.0064 0.0111 11.10 0.0217 21.70 27.78 7.813
16 0.385 320 0.0068 0.0068 0.0111 11.13 0.0217 21.65 27.78 7.808
17 0.409 340 0.0070 0.0070 0.0110 11.00 0.0217 21.65 27.78 7.777
18 0.433 360 0.0072 0.0072 0.0092 9.20 0.0217 21.70 27.78 7.360
19 0.457 380 0.0074 0.0074 0.0093 9.30 0.0217 21.68 27.78 7.379
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 10/30/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 74.0 %
After test 44.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0078 0.0078 0.0092 9.20 0.0217 21.70 27.78 7.360
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/1/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.8 %
After test 67.8 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 13.89 0.000
0.5 0.012 0.0002 0 0.0200 20.00 0.0009 0.90 3.47 4.978
1 0.024 20 0.0002 0.0002 0.0190 19.00 0.0009 0.90 13.89 4.740
2 0.048 40 0.0002 0.0002 0.0170 17.00 0.0010 1.00 13.89 4.288
3 0.072 60 0.0018 0.0018 0.0170 17.00 0.0012 1.20 13.89 4.335
4 0.096 80 0.0017 0.0017 0.0170 17.00 0.0015 1.50 13.89 4.407
5 0.120 100 0.0020 0.0020 0.0170 17.00 0.0017 1.70 13.89 4.454
6 0.144 120 0.0020 0.0020 0.0170 17.00 0.0017 1.70 13.89 4.454
7 0.168 140 0.0025 0.0025 0.0160 16.00 0.0016 1.60 13.89 4.192
8 0.192 160 0.0029 0.0029 0.0159 15.90 0.0016 1.55 13.89 4.157
9 0.216 180 0.0030 0.0030 0.0159 15.90 0.0015 1.50 13.89 4.145
10 0.241 200 0.0032 0.0032 0.0150 15.00 0.0015 1.50 13.89 3.930
11 0.265 220 0.0037 0.0037 0.0147 14.70 0.0015 1.47 13.89 3.852
12 0.289 240 0.0039 0.0039 0.0138 13.80 0.0014 1.38 13.89 3.616
13 0.313 260 0.0041 0.0041 0.0138 13.80 0.0014 1.38 13.89 3.616
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/6/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.0 %
After test 40.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 27.78 0.000
1 0.024 20 0.0010 0.0010 0.0160 16.00 0.0220 22.00 27.78 9.051
2 0.048 40 0.0012 0.0012 0.0152 15.20 0.0256 25.60 27.78 9.718
3 0.072 60 0.0019 0.0019 0.0145 14.50 0.0250 25.00 27.78 9.409
4 0.096 80 0.0020 0.0020 0.0139 13.90 0.0243 24.30 27.78 9.099
5 0.120 100 0.0027 0.0027 0.0136 13.55 0.0238 23.80 27.78 8.897
6 0.144 120 0.0030 0.0030 0.0131 13.10 0.0236 23.60 27.78 8.742
7 0.168 140 0.0033 0.0033 0.0128 12.80 0.0236 23.60 27.78 8.670
8 0.192 160 0.0038 0.0038 0.0126 12.60 0.0235 23.45 27.78 8.587
9 0.216 180 0.0040 0.0040 0.0125 12.50 0.0233 23.34 27.78 8.537
10 0.241 200 0.0044 0.0044 0.0123 12.30 0.0234 23.40 27.78 8.504
11 0.265 220 0.0045 0.0045 0.0123 12.25 0.0234 23.40 27.78 8.492
12 0.289 240 0.0050 0.0050 0.0121 12.13 0.0234 23.40 27.78 8.463
13 0.313 260 0.0051 0.0051 0.0122 12.17 0.0234 23.40 27.78 8.473
14 0.337 280 0.0055 0.0055 0.0121 12.05 0.0235 23.45 27.78 8.456
15 0.361 300 0.0058 0.0058 0.0120 12.03 0.0235 23.50 27.78 8.463
16 0.385 320 0.0060 0.0060 0.0120 12.03 0.0235 23.45 27.78 8.451
17 0.409 340 0.0060 0.0060 0.0120 12.00 0.0236 23.55 27.78 8.468
18 0.433 360 0.0060 0.0060 0.0119 11.90 0.0234 23.35 27.78 8.396
19 0.457 380 0.0060 0.0060 0.0119 11.87 0.0234 23.35 27.78 8.389
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/6/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.0 %
After test 40.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0058 0.0058 0.0119 11.86 0.0234 23.35 27.78 8.387
21 0.505 420 0.0058 0.0058 0.0119 11.85 0.0234 23.35 27.78 8.384
22 0.529 440 0.0058 0.0058 0.0118 11.80 0.0234 23.35 27.78 8.373
23 0.553 460 0.0057 0.0057 0.0118 11.80 0.0233 23.30 27.78 8.361
24 0.577 480 0.0057 0.0057 0.0118 11.78 0.0233 23.30 27.78 8.356
25 0.601 500 0.0057 0.0057 0.0118 11.78 0.0233 23.30 27.78 8.356
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/6/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 73.1 %
After test 75.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 3.47 0.000
1 0.024 20 0.0000 0.0000 0.0015 1.50 0.0019 1.90 3.47 0.810
2 0.048 40 0.0005 0.0005 0.0013 1.30 0.0016 1.60 3.47 0.691
3 0.072 60 0.0012 0.0012 0.0012 1.20 0.0018 1.80 3.47 0.715
4 0.096 80 0.0020 0.0020 0.0070 7.00 0.0011 1.10 3.47 1.929
5 0.120 100 0.0029 0.0029 0.0060 6.00 0.0012 1.20 3.47 1.715
6 0.144 120 0.0038 0.0038 0.0030 3.00 0.0010 1.00 3.47 0.953
7 0.168 140 0.0045 0.0045 0.0005 0.50 0.0009 0.90 3.47 0.333
8 0.192 160 0.0050 0.0050 0.0002 0.20 0.0009 0.90 3.47 0.262
9 0.216 180 0.0055 0.0055 0.0030 3.00 0.0011 1.10 3.47 0.977
10 0.241 200 0.0060 0.0060 0.0032 3.20 0.0013 1.25 3.47 1.060
11 0.265 220 0.0063 0.0063 0.0021 2.10 0.0015 1.50 3.47 0.858
12 0.289 240 0.0068 0.0068 0.0020 2.00 0.0017 1.70 3.47 0.881
13 0.313 260 0.0073 0.0073 0.0021 2.10 0.0021 2.10 3.47 1.000
14 0.337 280 0.0079 0.0079 0.0021 2.10 0.0024 2.35 3.47 1.060
15 0.361 300 0.0083 0.0083 0.0021 2.10 0.0021 2.10 3.47 1.000
16 0.385 320 0.0087 0.0087 0.0021 2.10 0.0021 2.10 3.47 1.000
17 0.409 340 0.0091 0.0091 0.0021 2.10 0.0023 2.30 3.47 1.048
18 0.433 360 0.0098 0.0098 0.0021 2.10 0.0024 2.40 3.47 1.072
19 0.457 380 0.0100 0.0100 0.0021 2.10 0.0024 2.40 3.47 1.072
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/6/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 73.1 %
After test 75.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0103 0.0103 0.0021 2.10 0.0023 2.30 3.47 1.048
21 0.505 420 0.0110 0.0110 0.0021 2.10 0.0024 2.40 3.47 1.072
22 0.529 440 0.0112 0.0112 0.0021 2.10 0.0024 2.40 3.47 1.072
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/8/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.0 %
After test 54.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 13.89 0.000
0.5 0.012 0.0000 0.0210 21.00 0.0110 11.00 13.89 7.622
1 0.024 20 0.0010 0.0010 0.0210 21.00 0.0110 11.00 13.89 7.622
2 0.048 40 0.0020 0.0020 0.0191 19.10 0.0105 10.50 13.89 7.051
3 0.072 60 0.0038 0.0038 0.0181 18.10 0.0105 10.50 13.89 6.812
4 0.096 80 0.0041 0.0041 0.0179 17.90 0.0103 10.30 13.89 6.717
5 0.120 100 0.0050 0.0050 0.0174 17.40 0.0099 9.90 13.89 6.503
6 0.144 120 0.0057 0.0057 0.0170 17.00 0.0097 9.65 13.89 6.348
7 0.168 140 0.0062 0.0062 0.0168 16.80 0.0096 9.60 13.89 6.288
8 0.192 160 0.0066 0.0066 0.0166 16.55 0.0097 9.70 13.89 6.253
9 0.216 180 0.0071 0.0071 0.0166 16.55 0.0098 9.75 13.89 6.265
10 0.241 200 0.0075 0.0075 0.0166 16.55 0.0097 9.70 13.89 6.253
11 0.265 220 0.0080 0.0080 0.0166 16.55 0.0097 9.70 13.89 6.253
12 0.289 240 0.0085 0.0085 0.0166 16.55 0.0098 9.75 13.89 6.265
13 0.313 260 0.0089 0.0089 0.0166 16.55 0.0098 9.78 13.89 6.272
14 0.337 280 0.0093 0.0093 0.0166 16.55 0.0098 9.80 13.89 6.276
15 0.361 300 0.0096 0.0096 0.0165 16.50 0.0099 9.90 13.89 6.288
16 0.385 320 0.0099 0.0099 0.0165 16.45 0.0104 10.35 13.89 6.384
17 0.409 340 0.0104 0.0104 0.0165 16.50 0.0102 10.20 13.89 6.360
18 0.433 360 0.0105 0.0105 0.0165 16.45 0.0102 10.20 13.89 6.348
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/8/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.0 %
After test 54.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
19 0.457 380 0.0110 0.0110 0.0166 16.60 0.0103 10.25 13.89 6.396
20 0.481 400 0.0113 0.0113 0.0166 16.60 0.0104 10.35 13.89 6.419
21 0.505 420 0.0115 0.0115 0.0163 16.30 0.0103 10.25 13.89 6.324
22 0.529 440 0.0118 0.0118 0.0162 16.15 0.0104 10.35 13.89 6.312
23 0.553 460 0.0120 0.0120 0.0159 15.90 0.0103 10.25 13.89 6.229
24 0.577 480 0.0124 0.0124 0.0160 15.98 0.0105 10.50 13.89 6.307
25 0.601 500 0.0125 0.0125 0.0159 15.90 0.0105 10.50 13.89 6.288
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/15/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.8 %
After test 67.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 6.94 0.000
0.5 0.012 0.0000 0.0079 7.90 0.0093 9.30 6.94 4.097
1 0.024 20 0.0004 0.0004 0.0064 6.40 0.0091 9.10 6.94 3.692
2 0.048 40 0.0007 0.0007 0.0049 4.90 0.0083 8.30 6.94 3.144
3 0.072 60 0.0009 0.0009 0.0041 4.10 0.0082 8.17 6.94 2.923
4 0.096 80 0.0011 0.0011 0.0033 3.30 0.0081 8.05 6.94 2.704
5 0.120 100 0.0014 0.0014 0.0027 2.70 0.0075 7.50 6.94 2.430
6 0.144 120 0.0015 0.0015 0.0025 2.50 0.0072 7.20 6.94 2.311
7 0.168 140 0.0017 0.0017 0.0025 2.45 0.0078 7.80 6.94 2.442
8 0.192 160 0.0018 0.0018 0.0024 2.36 0.0072 7.20 6.94 2.277
9 0.216 180 0.0019 0.0019 0.0023 2.30 0.0075 7.50 6.94 2.334
10 0.241 200 0.0020 0.0020 0.0022 2.22 0.0077 7.70 6.94 2.363
11 0.265 220 0.0021 0.0021 0.0022 2.22 0.0076 7.60 6.94 2.339
12 0.289 240 0.0022 0.0022 0.0023 2.30 0.0077 7.65 6.94 2.370
13 0.313 260 0.0022 0.0022 0.0022 2.22 0.0077 7.70 6.94 2.363
14 0.337 280 0.0023 0.0023 0.0021 2.06 0.0077 7.68 6.94 2.320
15 0.361 300 0.0024 0.0024 0.0020 1.98 0.0078 7.81 6.94 2.332
16 0.385 320 0.0024 0.0024 0.0019 1.85 0.0079 7.90 6.94 2.322
17 0.409 340 0.0025 0.0025 0.0018 1.80 0.0081 8.10 6.94 2.358
18 0.433 360 0.0026 0.0026 0.0018 1.78 0.0082 8.15 6.94 2.365
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/15/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.8 %
After test 67.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
19 0.457 380 0.0026 0.0026 0.0017 1.68 0.0082 8.20 6.94 2.353
20 0.481 400 0.0027 0.0027 0.0016 1.62 0.0083 8.27 6.94 2.356
21 0.505 420 0.0028 0.0028 0.0015 1.46 0.0082 8.20 6.94 2.301
22 0.529 440 0.0028 0.0028 0.0014 1.43 0.0084 8.40 6.94 2.341
23 0.553 460 0.0029 0.0029 0.0013 1.30 0.0084 8.40 6.94 2.311
24 0.577 480 0.0029 0.0029 0.0013 1.28 0.0085 8.45 6.94 2.318
25 0.601 500 0.0030 0.0030 0.0012 1.21 0.0087 8.70 6.94 2.361
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/16/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 73.1 %
After test 54.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 3.47 0.000
1 0.024 20 0.0050 0.0050 0.0022 2.15 0.0023 2.27 3.47 1.052
2 0.048 40 0.0050 0.0050 0.0021 2.10 0.0022 2.22 3.47 1.028
3 0.072 60 0.0050 0.0050 0.0021 2.05 0.0022 2.16 3.47 1.003
4 0.096 80 0.0050 0.0050 0.0020 2.00 0.0021 2.11 3.47 0.979
5 0.120 100 0.0050 0.0050 0.0020 1.98 0.0021 2.08 3.47 0.967
6 0.144 120 0.0050 0.0050 0.0020 1.98 0.0021 2.08 3.47 0.967
7 0.168 140 0.0050 0.0050 0.0020 1.98 0.0021 2.08 3.47 0.967
8 0.192 160 0.0050 0.0050 0.0020 1.95 0.0021 2.06 3.47 0.955
9 0.216 180 0.0050 0.0050 0.0020 1.95 0.0021 2.06 3.47 0.955
10 0.241 200 0.0050 0.0050 0.0020 1.95 0.0021 2.06 3.47 0.955
11 0.265 220 0.0050 0.0050 0.0020 1.95 0.0021 2.06 3.47 0.955
12 0.289 240 0.0050 0.0050 0.0020 1.95 0.0021 2.06 3.47 0.955
13 0.313 260 0.0055 0.0055 0.0019 1.90 0.0020 2.00 3.47 0.930
14 0.337 280 0.0060 0.0060 0.0018 1.81 0.0019 1.91 3.47 0.887
15 0.361 300 0.0060 0.0060 0.0018 1.78 0.0019 1.87 3.47 0.869
16 0.385 320 0.0060 0.0060 0.0017 1.73 0.0018 1.82 3.47 0.844
17 0.409 340 0.0060 0.0060 0.0017 1.70 0.0018 1.79 3.47 0.832
18 0.433 360 0.0060 0.0060 0.0017 1.68 0.0018 1.77 3.47 0.820
19 0.457 380 0.0060 0.0060 0.0017 1.69 0.0018 1.78 3.47 0.826
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/16/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 73.1 %
After test 54.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0060 0.0060 0.0017 1.65 0.0017 1.74 3.47 0.808
21 0.505 420 0.0060 0.0060 0.0016 1.63 0.0017 1.71 3.47 0.795
22 0.529 440 0.0060 0.0060 0.0016 1.63 0.0017 1.71 3.47 0.795
23 0.553 460 0.0060 0.0060 0.0016 1.60 0.0017 1.69 3.47 0.783
24 0.577 480 0.0060 0.0060 0.0017 1.65 0.0017 1.74 3.47 0.808
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/19/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.5 %
After test 55.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 6.94 0.000
1 0.024 20 0.0000 0.0000 0.0050 5.00 0.0106 10.55 6.94 3.704
2 0.048 40 0.0002 0.0002 0.0045 4.50 0.0095 9.50 6.94 3.334
3 0.072 60 0.0005 0.0005 0.0043 4.30 0.0091 9.07 6.94 3.185
4 0.096 80 0.0007 0.0007 0.0043 4.30 0.0091 9.07 6.94 3.185
5 0.120 100 0.0009 0.0009 0.0044 4.40 0.0093 9.28 6.94 3.259
6 0.144 120 0.0011 0.0011 0.0046 4.60 0.0097 9.71 6.94 3.408
7 0.168 140 0.0012 0.0012 0.0046 4.60 0.0097 9.71 6.94 3.408
8 0.192 160 0.0015 0.0015 0.0046 4.60 0.0097 9.71 6.94 3.408
9 0.216 180 0.0018 0.0018 0.0046 4.60 0.0097 9.71 6.94 3.408
10 0.241 200 0.0021 0.0021 0.0046 4.60 0.0097 9.71 6.94 3.408
11 0.265 220 0.0021 0.0021 0.0046 4.62 0.0097 9.75 6.94 3.422
12 0.289 240 0.0022 0.0022 0.0046 4.58 0.0097 9.66 6.94 3.393
13 0.313 260 0.0024 0.0024 0.0048 4.84 0.0102 10.21 6.94 3.585
14 0.337 280 0.0027 0.0027 0.0046 4.60 0.0097 9.71 6.94 3.408
15 0.361 300 0.0028 0.0028 0.0045 4.52 0.0095 9.54 6.94 3.348
16 0.385 320 0.0030 0.0030 0.0046 4.64 0.0098 9.79 6.94 3.437
17 0.409 340 0.0032 0.0032 0.0049 4.94 0.0104 10.42 6.94 3.660
18 0.433 360 0.0033 0.0033 0.0048 4.80 0.0101 10.13 6.94 3.556
19 0.457 380 0.0035 0.0035 0.0048 4.80 0.0101 10.13 6.94 3.556
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/19/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.5 %
After test 55.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0037 0.0037 0.0048 4.84 0.0102 10.21 6.94 3.585
21 0.505 420 0.0039 0.0039 0.0048 4.84 0.0102 10.21 6.94 3.585
22 0.529 440 0.0040 0.0040 0.0046 4.64 0.0098 9.79 6.94 3.437
23 0.553 460 0.0041 0.0041 0.0048 4.80 0.0101 10.13 6.94 3.556
24 0.577 480 0.0043 0.0043 0.0048 4.76 0.0100 10.04 6.94 3.526
25 0.601 500 0.0046 0.0046 0.0047 4.68 0.0099 9.87 6.94 3.467
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/20/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.1 %
After test #DIV/0! %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 13.89 0.000
1 0.024 20 0.0020 0.0020 0.0123 12.30 0.0130 12.98 13.89 6.021
2 0.048 40 0.0020 0.0020 0.0123 12.30 0.0130 12.98 13.89 6.021
3 0.072 60 0.0030 0.0030 0.0121 12.10 0.0128 12.77 13.89 5.923
4 0.096 80 0.0037 0.0037 0.0118 11.80 0.0124 12.45 13.89 5.776
5 0.120 100 0.0041 0.0041 0.0115 11.50 0.0121 12.13 13.89 5.629
6 0.144 120 0.0048 0.0048 0.0113 11.30 0.0119 11.92 13.89 5.531
7 0.168 140 0.0052 0.0052 0.0113 11.25 0.0119 11.87 13.89 5.507
8 0.192 160 0.0057 0.0057 0.0112 11.20 0.0118 11.82 13.89 5.482
9 0.216 180 0.0062 0.0062 0.0113 11.30 0.0119 11.92 13.89 5.531
10 0.241 200 0.0068 0.0068 0.0114 11.35 0.0120 11.97 13.89 5.556
11 0.265 220 0.0072 0.0072 0.0111 11.05 0.0117 11.66 13.89 5.409
12 0.289 240 0.0077 0.0077 0.0111 11.05 0.0117 11.66 13.89 5.409
13 0.313 260 0.0081 0.0081 0.0110 10.95 0.0116 11.55 13.89 5.360
14 0.337 280 0.0085 0.0085 0.0105 10.50 0.0111 11.08 13.89 5.140
15 0.361 300 0.0091 0.0091 0.0107 10.70 0.0113 11.29 13.89 5.238
16 0.385 320 0.0095 0.0095 0.0119 11.90 0.0126 12.55 13.89 5.825
17 0.409 340 0.0097 0.0097 0.0117 11.70 0.0123 12.34 13.89 5.727
18 0.433 360 0.0103 0.0103 0.0117 11.70 0.0123 12.34 13.89 5.727
19 0.457 380 0.0103 0.0103 0.0117 11.70 0.0123 12.34 13.89 5.727
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/22/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.4 %
After test #DIV/0! %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 27.78 0.000
1 0.024 20 0.0005 0.0005 0.0171 17.06 0.0207 20.69 27.78 8.992
2 0.048 40 0.0009 0.0009 0.0178 17.81 0.0216 21.60 27.78 9.387
3 0.072 60 0.0012 0.0012 0.0173 17.31 0.0210 20.99 27.78 9.124
4 0.096 80 0.0015 0.0015 0.0171 17.06 0.0207 20.69 27.78 8.992
5 0.120 100 0.0020 0.0020 0.0169 16.86 0.0204 20.45 27.78 8.887
6 0.144 120 0.0022 0.0022 0.0167 16.69 0.0202 20.23 27.78 8.794
7 0.168 140 0.0023 0.0023 0.0166 16.63 0.0202 20.16 27.78 8.762
8 0.192 160 0.0026 0.0026 0.0165 16.53 0.0200 20.04 27.78 8.712
9 0.216 180 0.0029 0.0029 0.0165 16.47 0.0200 19.97 27.78 8.679
10 0.241 200 0.0031 0.0031 0.0163 16.31 0.0198 19.78 27.78 8.597
11 0.265 220 0.0033 0.0033 0.0163 16.25 0.0197 19.70 27.78 8.564
12 0.289 240 0.0037 0.0037 0.0162 16.18 0.0196 19.61 27.78 8.524
13 0.313 260 0.0038 0.0038 0.0161 16.06 0.0195 19.48 27.78 8.465
14 0.337 280 0.0041 0.0041 0.0159 15.94 0.0193 19.32 27.78 8.399
15 0.361 300 0.0043 0.0043 0.0159 15.89 0.0193 19.27 27.78 8.376
16 0.385 320 0.0045 0.0045 0.0158 15.84 0.0192 19.21 27.78 8.350
17 0.409 340 0.0048 0.0048 0.0158 15.81 0.0192 19.17 27.78 8.333
18 0.433 360 0.0049 0.0049 0.0158 15.75 0.0191 19.10 27.78 8.300
19 0.457 380 0.0050 0.0050 0.0157 15.69 0.0190 19.02 27.78 8.267
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 11/22/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.4 %
After test #DIV/0! %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0052 0.0052 0.0158 15.81 0.0192 19.17 27.78 8.333
21 0.505 420 0.0053 0.0053 0.0156 15.63 0.0189 18.95 27.78 8.235
22 0.529 440 0.0055 0.0055 0.0155 15.53 0.0188 18.83 27.78 8.185
23 0.553 460 0.0060 0.0060 0.0155 15.50 0.0188 18.79 27.78 8.169
24 0.577 480 0.0061 0.0061 0.0155 15.47 0.0188 18.76 27.78 8.152
25 0.601 500 0.0062 0.0062 0.0154 15.38 0.0186 18.64 27.78 8.103
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/2/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.0 %
After test 44.1 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 27.78 0.000
1 0.024 20 0.0010 0.0010 0.0144 14.40 0.0176 17.60 27.78 7.622
2 0.048 40 0.0012 0.0012 0.0137 13.68 0.0205 20.48 27.78 8.137
3 0.072 60 0.0019 0.0019 0.0131 13.05 0.0200 20.00 27.78 7.872
4 0.096 80 0.0020 0.0020 0.0125 12.51 0.0194 19.44 27.78 7.610
5 0.120 100 0.0027 0.0027 0.0122 12.20 0.0190 19.04 27.78 7.440
6 0.144 120 0.0030 0.0030 0.0118 11.79 0.0189 18.88 27.78 7.305
7 0.168 140 0.0033 0.0033 0.0115 11.52 0.0189 18.88 27.78 7.241
8 0.192 160 0.0038 0.0038 0.0113 11.34 0.0188 18.76 27.78 7.170
9 0.216 180 0.0040 0.0040 0.0113 11.25 0.0187 18.67 27.78 7.127
10 0.241 200 0.0044 0.0044 0.0111 11.07 0.0187 18.72 27.78 7.096
11 0.265 220 0.0045 0.0045 0.0110 11.03 0.0187 18.72 27.78 7.085
12 0.289 240 0.0050 0.0050 0.0109 10.92 0.0187 18.72 27.78 7.059
13 0.313 260 0.0051 0.0051 0.0110 10.95 0.0187 18.72 27.78 7.068
14 0.337 280 0.0055 0.0055 0.0108 10.85 0.0188 18.76 27.78 7.052
15 0.361 300 0.0058 0.0058 0.0108 10.83 0.0188 18.80 27.78 7.057
16 0.385 320 0.0060 0.0060 0.0108 10.83 0.0188 18.76 27.78 7.048
17 0.409 340 0.0060 0.0060 0.0108 10.80 0.0188 18.84 27.78 7.060
18 0.433 360 0.0060 0.0060 0.0107 10.71 0.0187 18.68 27.78 7.001
19 0.457 380 0.0060 0.0060 0.0107 10.68 0.0187 18.68 27.78 6.994
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/2/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 2 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.0 %
After test 44.1 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0058 0.0058 0.0107 10.67 0.0187 18.68 27.78 6.992
21 0.505 420 0.0058 0.0058 0.0107 10.67 0.0187 18.68 27.78 6.990
22 0.529 440 0.0058 0.0058 0.0106 10.62 0.0187 18.68 27.78 6.979
23 0.553 460 0.0057 0.0057 0.0106 10.62 0.0186 18.64 27.78 6.970
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/13/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.8 %
After test ‐114.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 3.47 0.000
1 0.024 20 0.0015 0.0015 0.0002 0.20 0.0064 6.40 3.47 1.572
2 0.048 40 0.0025 0.0025 0.0002 0.20 0.0062 6.20 3.47 1.524
3 0.072 60 0.0030 0.0030 0.0002 0.20 0.0062 6.20 3.47 1.524
4 0.096 80 0.0035 0.0035 0.0002 0.20 0.0056 5.60 3.47 1.382
5 0.120 100 0.0040 0.0040 0.0002 0.20 0.0062 6.20 3.47 1.524
6 0.144 120 0.0046 0.0046 0.0001 0.10 0.0043 4.30 3.47 1.048
7 0.168 140 0.0051 0.0051 0.0001 0.10 0.0037 3.70 3.47 0.905
8 0.192 160 0.0053 0.0053 0.0001 0.10 0.0031 3.10 3.47 0.762
9 0.216 180 0.0057 0.0057 0.0002 0.15 0.0036 3.60 3.47 0.893
10 0.241 200 0.0061 0.0061 0.0001 0.10 0.0036 3.60 3.47 0.881
11 0.265 220 0.0063 0.0063 0.0001 0.10 0.0034 3.40 3.47 0.834
12 0.289 240 0.0068 0.0068 0.0001 0.10 0.0032 3.20 3.47 0.786
13 0.313 260 0.0070 0.0070 0.0003 0.25 0.0032 3.20 3.47 0.822
14 0.337 280 0.0074 0.0074 0.0003 0.25 0.0032 3.20 3.47 0.822
15 0.361 300 0.0078 0.0078 0.0003 0.25 0.0032 3.20 3.47 0.822
16 0.385 320 0.0080 0.0080 0.0004 0.35 0.0032 3.20 3.47 0.846
17 0.409 340 0.0082 0.0082 0.0004 0.35 0.0032 3.20 3.47 0.846
18 0.433 360 0.0085 0.0085 0.0003 0.25 0.0032 3.20 3.47 0.822
19 0.457 380 0.0088 0.0088 0.0003 0.25 0.0032 3.20 3.47 0.822
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/13/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 72.8 %
After test ‐114.7 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0091 0.0091 0.0002 0.20 0.0032 3.20 3.47 0.810
21 0.505 420 0.0094 0.0094 0.0002 0.20 0.0032 3.20 3.47 0.810
22 0.529 440 0.0101 0.0101 0.0002 0.15 0.0032 3.20 3.47 0.798
23 0.553 460 0.0104 0.0104 0.0010 1.00 0.0032 3.20 3.47 1.000
24 0.577 480 0.0109 0.0109 0.0010 1.00 0.0032 3.20 3.47 1.000
25 0.601 500 0.0112 0.0112 0.0010 1.00 0.0032 3.20 3.47 1.000
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/13/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.8 %
After test 60.2 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 3.47 0.000
0.5 0.012 0.0000 0.0026 2.60 0.0021 2.10 3.47 1.120
1 0.024 20 0.0000 0.0000 0.0022 2.20 0.0018 1.80 3.47 0.953
2 0.048 40 0.0025 0.0025 0.0021 2.05 0.0020 1.95 3.47 0.953
3 0.072 60 0.0031 0.0031 0.0018 1.80 0.0018 1.80 3.47 0.858
4 0.096 80 0.0040 0.0040 0.0020 1.95 0.0020 2.00 3.47 0.941
5 0.120 100 0.0052 0.0052 0.0025 2.50 0.0025 2.50 3.47 1.191
6 0.144 120 0.0059 0.0059 0.0021 2.10 0.0022 2.20 3.47 1.024
7 0.168 140 0.0068 0.0068 0.0018 1.80 0.0022 2.20 3.47 0.953
8 0.192 160 0.0072 0.0072 0.0015 1.50 0.0020 2.00 3.47 0.834
9 0.216 180 0.0081 0.0081 0.0010 1.00 0.0020 2.00 3.47 0.715
10 0.241 200 0.0088 0.0088 0.0009 0.92 0.0022 2.20 3.47 0.743
11 0.265 220 0.0094 0.0094 0.0007 0.70 0.0020 2.00 3.47 0.643
12 0.289 240 0.0100 0.0100 0.0007 0.65 0.0021 2.10 3.47 0.655
13 0.313 260 0.0108 0.0108 0.0005 0.52 0.0021 2.10 3.47 0.624
14 0.337 280 0.0111 0.0111 0.0005 0.48 0.0021 2.10 3.47 0.615
15 0.361 300 0.0119 0.0119 0.0001 0.10 0.0021 2.10 3.47 0.524
16 0.385 320 0.0112 0.0112 0.0001 0.10 0.0021 2.10 3.47 0.524
17 0.409 340 0.0130 0.0130 0.0000 0.00 0.0021 2.10 3.47 0.500
18 0.433 360 0.0133 0.0133 0.0000 0.00 0.0020 2.00 3.47 0.476
19 0.457 380 0.0140 0.0140 0.0000 0.00 0.0019 1.90 3.47 0.453
20 0.481 400 0.0142 0.0142 0.0000 0.00 0.0020 2.00 3.47 0.476
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/13/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 74.9 %
After test 58.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 6.94 0.000
1 0.024 20 0.0005 0.0005 0.0059 5.85 0.0085 8.50 6.94 3.418
2 0.048 40 0.0010 0.0010 0.0059 5.85 0.0084 8.40 6.94 3.394
3 0.072 60 0.0013 0.0013 0.0059 5.90 0.0082 8.20 6.94 3.359
4 0.096 80 0.0017 0.0017 0.0059 5.90 0.0081 8.10 6.94 3.335
5 0.120 100 0.0021 0.0021 0.0059 5.90 0.0080 8.02 6.94 3.316
6 0.144 120 0.0025 0.0025 0.0059 5.90 0.0080 8.00 6.94 3.311
7 0.168 140 0.0028 0.0028 0.0059 5.90 0.0080 8.00 6.94 3.311
8 0.192 160 0.0030 0.0030 0.0059 5.85 0.0080 7.95 6.94 3.287
9 0.216 180 0.0034 0.0034 0.0058 5.80 0.0079 7.90 6.94 3.263
10 0.241 200 0.0038 0.0038 0.0059 5.87 0.0079 7.85 6.94 3.268
11 0.265 220 0.0041 0.0041 0.0058 5.75 0.0079 7.85 6.94 3.239
12 0.289 240 0.0043 0.0043 0.0057 5.70 0.0078 7.80 6.94 3.216
13 0.313 260 0.0046 0.0046 0.0057 5.65 0.0078 7.75 6.94 3.192
14 0.337 280 0.0049 0.0049 0.0057 5.65 0.0076 7.60 6.94 3.156
15 0.361 300 0.0051 0.0051 0.0057 5.65 0.0076 7.60 6.94 3.156
16 0.385 320 0.0053 0.0053 0.0056 5.62 0.0077 7.65 6.94 3.161
17 0.409 340 0.0055 0.0055 0.0057 5.68 0.0076 7.63 6.94 3.170
18 0.433 360 0.0058 0.0058 0.0056 5.60 0.0076 7.62 6.94 3.149
19 0.457 380 0.0061 0.0061 0.0056 5.60 0.0076 7.62 6.94 3.149
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 12/13/2013
Test Type: Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 2 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in²
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 74.9 %
After test 58.3 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0065 0.0065 0.0056 5.60 0.0076 7.62 6.94 3.149
21 0.505 420 0.0065 0.0065 0.0056 5.60 0.0077 7.65 6.94 3.156
22 0.529 440 0.0067 0.0067 0.0056 5.60 0.0077 7.67 6.94 3.161
23 0.553 460 0.0069 0.0069 0.0056 5.60 0.0077 7.67 6.94 3.161
Page 2 of 2
164
Appendix E - Overly Consolidated Ring Shear Adhesion Test,
Laboratory Observations
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/7/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 8.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 71.9 %
After test 48.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 3.47 0.000
1 0.024 20 0.0000 0.0000 0.0213 21.30 0.0290 29.00 3.47 11.981
2 0.048 40 0.0000 0.0000 0.0208 20.80 0.0278 27.80 3.47 11.576
3 0.072 60 0.0000 0.0000 0.0201 20.10 0.0264 26.40 3.47 11.076
4 0.096 80 0.0000 0.0000 0.0191 19.10 0.0255 25.50 3.47 10.624
5 0.120 100 0.0000 0.0000 0.0187 18.70 0.0246 24.60 3.47 10.314
6 0.144 120 0.0000 0.0000 0.0183 18.30 0.0234 23.40 3.47 9.933
7 0.168 140 0.0002 0.0002 0.0181 18.10 0.0222 22.20 3.47 9.599
8 0.192 160 0.0003 0.0003 0.0178 17.80 0.0219 21.90 3.47 9.456
9 0.216 180 0.0005 0.0005 0.0176 17.60 0.0215 21.50 3.47 9.313
10 0.241 200 0.0006 0.0006 0.0175 17.50 0.0212 21.20 3.47 9.218
11 0.265 220 0.0006 0.0006 0.0173 17.30 0.0211 21.10 3.47 9.147
12 0.289 240 0.0007 0.0007 0.0171 17.10 0.0209 20.90 3.47 9.051
13 0.313 260 0.0009 0.0009 0.0170 17.00 0.0208 20.80 3.47 9.004
14 0.337 280 0.0009 0.0009 0.0170 17.00 0.0207 20.70 3.47 8.980
15 0.361 300 0.0010 0.0010 0.0170 17.00 0.0207 20.65 3.47 8.968
16 0.385 320 0.0010 0.0010 0.0169 16.90 0.0206 20.60 3.47 8.932
17 0.409 340 0.0010 0.0010 0.0168 16.80 0.0206 20.60 3.47 8.909
18 0.433 360 0.0010 0.0010 0.0167 16.70 0.0206 20.60 3.47 8.885
19 0.457 380 0.0010 0.0010 0.0167 16.70 0.0205 20.50 3.47 8.861
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/7/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.25 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 8.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 71.9 %
After test 48.6 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0010 0.0010 0.0166 16.60 0.0205 20.50 3.47 8.837
21 0.505 420 0.0010 0.0010 0.0166 16.55 0.0205 20.50 3.47 8.825
22 0.529 440 0.0011 0.0011 0.0165 16.50 0.0205 20.45 3.47 8.801
23 0.553 460 0.0011 0.0011 0.0165 16.50 0.0205 20.45 3.47 8.801
24 0.577 480 0.0011 0.0011 0.0163 16.30 0.0204 20.40 3.47 8.742
25 0.601 500 0.0012 0.0012 0.0162 16.20 0.0204 20.40 3.47 8.718
26 0.625 520 0.0012 0.0012 0.0162 16.20 0.0204 20.35 3.47 8.706
27 0.649 540 0.0012 0.0012 0.0162 16.15 0.0203 20.30 3.47 8.682
28 0.673 560 0.0013 0.0013 0.0161 16.10 0.0203 20.30 3.47 8.670
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/13/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 2.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.9 %
After test 41.0 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 13.89 0.000
1 0.024 20 0.0000 0.0000 0.0250 25.00 0.0185 18.50 13.89 10.362
2 0.048 40 ‐0.0050 ‐0.0050 0.0241 24.10 0.0178 17.80 13.89 9.980
3 0.072 60 ‐0.0070 ‐0.0070 0.0232 23.20 0.0171 17.10 13.89 9.599
4 0.096 80 ‐0.0060 ‐0.0060 0.0228 22.80 0.0168 16.80 13.89 9.433
5 0.120 100 ‐0.0040 ‐0.0040 0.0221 22.10 0.0160 16.00 13.89 9.075
6 0.144 120 ‐0.0020 ‐0.0020 0.0218 21.80 0.0156 15.60 13.89 8.909
7 0.168 140 ‐0.0020 ‐0.0020 0.0218 21.80 0.0155 15.50 13.89 8.885
8 0.192 160 ‐0.0010 ‐0.0010 0.0214 21.40 0.0152 15.20 13.89 8.718
9 0.216 180 0.0000 0.0000 0.0213 21.30 0.0151 15.10 13.89 8.670
10 0.241 200 0.0000 0.0000 0.0212 21.20 0.0151 15.10 13.89 8.647
11 0.265 220 0.0000 0.0000 0.0208 20.80 0.0148 14.80 13.89 8.480
12 0.289 240 0.0010 0.0010 0.0208 20.80 0.0146 14.60 13.89 8.432
13 0.313 260 0.0010 0.0010 0.0207 20.70 0.0145 14.50 13.89 8.384
14 0.337 280 0.0020 0.0020 0.0206 20.60 0.0145 14.50 13.89 8.361
15 0.361 300 0.0020 0.0020 0.0206 20.60 0.0144 14.40 13.89 8.337
16 0.385 320 0.0020 0.0020 0.0206 20.60 0.0143 14.30 13.89 8.313
17 0.409 340 0.0030 0.0030 0.0205 20.50 0.0143 14.30 13.89 8.289
18 0.433 360 0.0030 0.0030 0.0204 20.40 0.0142 14.20 13.89 8.242
19 0.457 380 0.0040 0.0040 0.0204 20.40 0.0142 14.20 13.89 8.242
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/13/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 1 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 2.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 70.9 %
After test 41.0 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0050 0.0050 0.0204 20.40 0.0142 14.20 13.89 8.242
21 0.505 420 0.0060 0.0060 0.0204 20.40 0.0141 14.10 13.89 8.218
22 0.529 440 0.0070 0.0070 0.0203 20.30 0.0141 14.10 13.89 8.194
23 0.553 460 0.0080 0.0080 0.0203 20.30 0.0141 14.10 13.89 8.194
24 0.577 480 0.0090 0.0090 0.0202 20.20 0.0140 14.00 13.89 8.146
25 0.601 500 0.0100 0.0100 0.0202 20.20 0.0140 14.00 13.89 8.146
26 0.625 520 0.0100 0.0100 0.0202 20.20 0.0140 14.00 13.89 8.146
27 0.649 540 0.0100 0.0100 0.0202 20.20 0.0140 14.00 13.89 8.146
Page 2 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/20/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 4.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 71.2 %
After test 45.5 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
0 0.000 0 0.0000 ‐ 0.0000 0.00 0.0000 0.00 6.94 0.000
1 0.024 20 0.0000 0.0000 0.0222 22.20 0.0247 24.70 6.94 11.171
2 0.048 40 ‐0.0010 ‐0.0010 0.0215 21.50 0.0239 23.90 6.94 10.814
3 0.072 60 ‐0.0020 ‐0.0020 0.0205 20.50 0.0229 22.90 6.94 10.338
4 0.096 80 ‐0.0030 ‐0.0030 0.0194 19.40 0.0220 22.00 6.94 9.861
5 0.120 100 ‐0.0030 ‐0.0030 0.0191 19.10 0.0215 21.50 6.94 9.671
6 0.144 120 ‐0.0020 ‐0.0020 0.0185 18.50 0.0211 21.10 6.94 9.433
7 0.168 140 ‐0.0010 ‐0.0010 0.0181 18.10 0.0208 20.80 6.94 9.266
8 0.192 160 ‐0.0010 ‐0.0010 0.0178 17.80 0.0206 20.60 6.94 9.147
9 0.216 180 ‐0.0010 ‐0.0010 0.0174 17.40 0.0203 20.30 6.94 8.980
10 0.241 200 ‐0.0010 ‐0.0010 0.0171 17.05 0.0201 20.05 6.94 8.837
11 0.265 220 ‐0.0010 ‐0.0010 0.0169 16.85 0.0199 19.90 6.94 8.754
12 0.289 240 0.0000 0.0000 0.0165 16.50 0.0196 19.60 6.94 8.599
13 0.313 260 0.0000 0.0000 0.0163 16.30 0.0196 19.60 6.94 8.551
14 0.337 280 0.0000 0.0000 0.0163 16.30 0.0196 19.60 6.94 8.551
15 0.361 300 0.0000 0.0000 0.0161 16.10 0.0196 19.60 6.94 8.504
16 0.385 320 0.0010 0.0010 0.0159 15.90 0.0194 19.40 6.94 8.408
17 0.409 340 0.0010 0.0010 0.0157 15.70 0.0191 19.10 6.94 8.289
18 0.433 360 0.0010 0.0010 0.0155 15.50 0.0190 19.00 6.94 8.218
19 0.457 380 0.0010 0.0010 0.0155 15.50 0.0190 19.00 6.94 8.218
Page 1 of 2
Laboratory Test: Ring Shear ‐ Adhesion Test
Material Type: Kaolin (white)
Date: 2/20/2014
Test Type: Over‐Consolidated Undrained
Ring Volume Test Parameters
Inside diameter 2.756 inches Ring Roughness Coefficent 20 µm
Outside diameter 3.937 inches Confining Pressure: 0.5 tsf
thickness 1.181 inches Gear Ratio: 30‐60
height 0.197 inches Speed: 3.0 Deg/Min
Area 6.21 in² OCR: 4.0
Volume 1.22 in3 Moisture Content
Tourqu are length 2.5 in Prior to test 71.2 %
After test 45.5 %
Degrees
Shear
Displacement
(in)
Time (sec)Vertical Gage
Reading (in)
Consolidation
(in)
South Force
Gage Reading
(in)
South Force
Gage Reading
(lbs)
North Force
Gage Reading
(in)
North Force
Gage Reading
(lbs)
Normal
Stress
(psi)
Shear
Stress
(psi)
20 0.481 400 0.0015 0.0015 0.0153 15.30 0.0189 18.90 6.94 8.146
21 0.505 420 0.0020 0.0020 0.0152 15.20 0.0189 18.90 6.94 8.122
22 0.529 440 0.0020 0.0020 0.0151 15.05 0.0188 18.80 6.94 8.063
23 0.553 460 0.0025 0.0025 0.0150 15.00 0.0188 18.80 6.94 8.051
24 0.577 480 0.0025 0.0025 0.0149 14.90 0.0188 18.80 6.94 8.027
25 0.601 500 0.0030 0.0030 0.0149 14.90 0.0188 18.80 6.94 8.027
26 0.625 520 0.0030 0.0030 0.0148 14.80 0.0187 18.70 6.94 7.980
27 0.649 540 0.0030 0.0030 0.0148 14.80 0.0185 18.50 6.94 7.932
Page 2 of 2