development, installation and testing of an innovative ......development, installation and testing...
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Development, Installation and Testing of an
Innovative Epoxy Anchored Screw Pile
Thesis submitted in fulfilment of the requirements for the degree
of
Masters of Engineering (by Research)
by
John George Agius
(Student Number 491824x)
Department of Civil Engineering
Swinburne University, Hawthorn Campus, Melbourne, Australia
2015
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Abstract This thesis details the development and the installation of a new application of
foundations for cable stays that can be used in areas where ground conditions
present good to very good rock under a layer of soil either clay or sand. The Epoxy
Anchored Screw Pile presented in this work make screw piles a viable stand-alone
option in all ground conditions including early refusal on rock through the addition
of an epoxied socket. The aim is to reduce the displacement at the head of the screw
pile with the addition of an epoxied socket. This was achieved through the
development of a practical installation methodology and full scale testing which is
documented in this thesis. The results from the testing show that the socket can
provide an increase in tensile capacity and reduce the displacement by a factor of up
to 20 at similar loads to that of a screw pile without the epoxy socket. The addition
of the epoxy socket required only hand tools and can be installed rapidly.
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Acknowledgements I would like to thank and am very grateful for the encouragement, support and
assistance from the following people:
James Murray-Parkes of Engineering Innovations Group who is the innovator
responsible for the concept detailed in this thesis as one of many of his new
innovations. James supported and fought for me tirelessly to help make this thesis
possible. He introduced me to many across the industry and has helped to support
me by providing employment opportunities and introducing me to his vast network
of friends and colleagues. I am indebted to him for his friendship, endless support
and all of the opportunities he has provided me. Without James my postgraduate
studies would not have been possible. He is a brilliant engineer and physicist and I
offer him my deepest thanks for all the hard work and assistance he has given.
Professor Jay Sanjayan of Swinburne University for helping to direct and guide me
in the completion of my masterβs thesis. Jay has provided many thoughtful insights
and has helped to point me in the right direction to complete this thesis. Jay has been
very supportive during the completion of this thesis.
Michael Kennedy, Dene Ward and all staff involved in the Elaine Terminal Station
from Powercor Network Services, for providing a site and a funding for the
installation and testing for this thesis. I have been very lucky to be able to work for
both Mike and Dene who have helped with my development offering kind words of
support and encouragement. I would like to add a special thanks to Mike as he was a
big factor in my decision to pursue the completion of this thesis, as the project
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manager for the Elaine Terminal Station Mike put together a great project team and
helped make the project very enjoyable.
Peter Healy and Simon Hughes of Hollow Core Concrete who provided funding for
my scholarship and encouraged me to undertake and complete this thesis.
Darren Barnett and Trident Civil Group for providing advice and staff of the highest
quality to help with the installation and construction of the Epoxy Anchored Screw
Pile.
Stewart Nipperess and SFL Piletech who helped with the development of the Epoxy
Anchored Screw Pile, installed the screw piles and provided the testing equipment
for this thesis.
Frank Albrecht, Sivanerupan Sivagnanasundram and Robert Cornish of
Engineering Innovations Group for helping with technical advice and
supporting me to expand my knowledge in the field of civil engineering.
My fellow colleges and friends for their support and encouragement during the
completion of my thesis.
I would also like to thank my family and my girlfriend Tamara for the love,
encouragement and support that they have provided me.
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Declarations This thesis contains no material that has been accepted for the award of any other
degree or diploma at any university or other institution. To the best of my
knowledge the thesis contains no material previously published or written by
another person, except where due reference is made.
John George Agius
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Contents
1. Introduction ................................................................................................................................. 9
1.1. Preface ........................................................................................................................................ 9
1.1.1. Screw Piles ....................................................................................................................... 9
1.1.2. Rock Anchors ............................................................................................................... 11
1.1.3. Bonded Rock Bolts ...................................................................................................... 13
1.1.4. Bond Strength of Cemented Grouts ........................................................................ 17
1.1.5. Bonded Chemical Anchors in Concrete ................................................................ 21
1.1.6. Tension Piles .................................................................................................................. 24
1.1.7. Load Bearing Capacity Based on Settlement ....................................................... 26
1.1.8. Drill Types and Selection ............................................................................................. 29
1.1.9. Hoek-Brown Criterion .................................................................................................. 30
1.1.10. Rock Mass Classifications ........................................................................................... 32
1.1.11. Mohr-Coulomb Strength Criterion ............................................................................ 34
1.1.12. Deflection Limits of Transmission Poles ..................... Error! Bookmark not defined.
2. Existing Tension Foundation Systems ..................................................................................... 37
2.1. Dead Man Anchors .................................................................................................................. 37
2.2. Bored Concrete Piles ............................................................................................................... 39
2.3. Helical Screw Piles .................................................................................................................. 41
2.4. Rock Anchors .......................................................................................................................... 42
2.5. Summary of Cable Stay Foundation Suitability ....................................................................... 46
2.6. Outline ..................................................................................................................................... 47
3. Innovative Epoxy Anchored Screw Pile and Installation Methodology ............................... 48
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3.1. List of Material to be installed .................................................................................................. 51
3.2. Equipment needed for the Installation ...................................................................................... 55
3.3. Method ..................................................................................................................................... 58
3.3.1. Test Installation ............................................................................................................. 58
3.3.2. Epoxy Anchor Installation Method ........................................................................... 67
3.3.3. Issues Encountered During Anchor Installation ...................................................... 89
4. Test Details of the new Epoxy Anchored Screw Pile .............................................................. 94
5. Estimation of the load capacity of the Epoxy Anchored Screw Pile ................................... 101
5.1. Failure Mechanisms................................................................................................................ 101
5.2. Screw Pile ............................................................................................................................... 102
5.3. Epoxy Anchor Failure ............................................................................................................ 104
5.3.1. Slip Failure ................................................................................................................... 104
5.3.2. Cone Failure .............................................................................................................. 109
5.3.3. Steel Failure ................................................................................................................ 113
6. Test Results .............................................................................................................................. 115
6.1. Screw Pile Only ...................................................................................................................... 115
6.2. Epoxy Anchored Screw Pile ................................................................................................... 119
7. Conclusions .............................................................................................................................. 130
8. Recommendations ................................................................................................................... 133
9. References ................................................................................................................................ 134
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1. Introduction
Development, Installation and Testing of an innovative Epoxy Anchored Screw Pile
1.1. Preface
The first section of this thesis details the research done into anchors, piles, rock
mechanics and rock bolts. The development of the innovative Epoxy Anchored
Screw Pile presented in this thesis came from a combination of current research into
tension piles, screw piles and bonded anchors and was adapted to suit the varying
ground conditions that were seen on the Elaine Terminal Station Transmission Line
where no singular conventional foundation system was suitable and the innovative
Epoxy Anchored Screw Pile was tested and installed.
1.1.1. Screw Piles
Screw Piles (also known as Helical Piles) are a form of deep foundation that can
provide tensile, compressive and lateral resistance to a structure. They are very cost
effective foundations for structures, as they can be installed quickly and loaded
immediately. Screw piles are a form of replacement pile generally comprising of a
steel shaft and one or more helices (bearing plates) welded to the shaft at various
spacing. Screw piles can be installed quickly using an excavator with a rotary drive
motor. They do not require dewatering nor do they generate any spoil. Screw piles
can be installed in a range of materials from soft clays and loose sands to dense
clays or extremely weathered rock. However screw piles are currently not suitable in
areas with unweathered rock as the pile cannot penetrate through a layer of rock.
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Helix
Steel Tube
Figure 1-1 - Detail of Screw Pile
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1.1.2. Rock Anchors
Tomlinson and Woodward (2008) define rock anchors as tension piles that can be
used when the overburden pressure from the soil is insufficient to develop the
required uplift capacity. Rock anchors comprise of a bored hole with either a
mechanical or bonded anchor. Drilling in hard rock can be expensive and requires
specialised machine mounted drilling equipment. The resistance of a single rock
anchor is determined by 4 key factors
β’ Safe working stress of the steel anchor
β’ Bond stress between the steel and the grout or bonding material
β’ Bond stress between the grout or bonding material and rock
β’ The dead weight of the mass of rock that may be mobilised if the bond or
anchor does not fail and rock cone failure occurs
Rock anchors can be installed in areas where a sufficient layer of rock is present to
gain the required uplift capacity through the above mechanisms.
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Figure 1-1a - Installation of Rock Anchor
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1.1.3. Bonded Rock Bolts
There are several different publications that provide guidelines for depths of resin or
epoxy grouted rock anchors in different varieties of rock. Figures 1-2 and 1-3 are
based on the results of anchor tests provide a guideline for the design and
installation of grouted or resin grouted rock bolts. Figures 1-2 and1-3 show the
results of some of these tests. The results from Schroder and Swanson (1992) were
based on very weak rock found in the Southeast region of Alaska.
Figure 1-2 - Ultimate anchor capacity vs. depth (bond length) for grouted rock anchors.
(Schroder and Swanson 1992)
kips = 4.448 kN
inches = 25.4 mm
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Figure 1-3 - - Ultimate anchor capacity vs. depth (bond length) for grouted rock anchors in
different rock. (Schroder and Swanson 1992)
kips = 4.448 kN
inches = 25.4 mm
The above figure (Figure 1-3) shows the relationship between bond length and
anchorage strength for different varieties of rock from DYWIDAG-Systems
International Canada Ltd.
Littlejohn and Bruce (1977) discussed the relationship between cement grouts and
rock. They demonstrated that when slip failure of a rock bolting system occurs it
will do so at either the grout bar interface or the grout rock interface. They
determined that the maximum strength of the grout/rock interface should be a
function of the shear strength with an appropriate safety factor (not less than 2).
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However, this was said to apply mainly to βsoft rocksβ with a UCS (Unconfined
Compressive Strength) less than 7 MPa. Littlejohn (1972) stated that the ultimate
bond strength in massive rocks (100% core recovery) should be 10% of their
uniaxial compressive strength up to a maximum of 4.2 MPa.
The shear strength can be found using the Mohr β Coulomb strength criterion as
long as the CS and internal friction angle are known. Littlejohn and Bruce (1977)
provided the following table and equation to calculate the ultimate shear strength
base on the Mohr-Coulomb Criterion.
Figure 1-4 - Relationship between shear stress and uniaxial compressive strength. (Littlejohn
and Bruce 1977)
Ο = axial stress; Ο = shear stress; Ο = internal friction angle
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The bond strength at the rock/grout interface is, however, highly dependent on the
degree of weathering of the rock, with research of Saliman and Schaefer (1968)
showing the capacity of bond strengths in weathered rock is less than 0.1 MPa. This
makes geotechnical assessment and testing of each anchor location very important.
The assessment of the anchor location should be conducted during the drilling of
anchors to guarantee that the required bond strength will be achieved.
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1.1.4. Bond Strength of Cemented Grouts
Mechanics of load transfer between the anchor, grout and rock.
A tensile load is transferred through a steel bar bonded to rock using a grout or
epoxy. There is shear transfer between two interfaces including the rock / grout
interface or the steel / grout interface. Although the distribution of shear stress varies
depending on embedment depth and strength, simple linear models have been used
to calculate the ultimate bond strength of bonded anchors.
Aldorf and Exner (1986) used the following equation for the calculation of the
strength of grouted rock bolts:
π· = π Γπ ΓπΓπͺπ
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.Equation 1-1
π = Capacity
π = Diameter
π = Length
πΆ = Bond Strength
π = Reduction factor / Safety coefficient
Benmokrane et al. (1995) conducted a laboratory study on six different cement
based grouts and two different steel rock anchors to derive an empirical equation for
the estimation of anchor pull-out resistance.
The cementitious grouts used in the study were comprised of different combinations
of water, Portland cement, silica fume, aluminium powder, water, sand and
superplasticisers. The steel anchors used included a conventional 7 strand cable bolt
and a Dywidag threaded bar with a diameter of 15.8mm.
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Concrete samples used to emulate rock had a compressive strength of 60 MPa and a
modulus of elasticity of 30 GPa. . 38mm diameter holes were drilled using a
percussive rotary drill and varying embedment depths ranging from 7 to 20 bar
diameters.
Figures 1-5 and 1-6 from Benmokrane et al. (1995) of results from these tests show
that the superior mechanical interlock between the grout and anchor provided by the
Dywidag bar provided maximum average bond stress nearly three times greater to
that of the smooth 7 stranded cable.
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Figure 1-5 - Typical shear bond stress-slip relationship (Benmokrane et al. (1995))
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Figure 1-6 - Influence of anchored length on the load displacement behaviour.
(Benmokrane et al. (1995))
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As can be expected the relationship between anchor length (AL) and load
displacement behaviour is close to linear, with load displacement behaviour
increasing at the same rate as the increase in anchor length.
A Kilic et al. (2002) also tested the pull-out load of anchors (reinforcement bars)
bonded to basalt blocks using cement based grouts. The tests investigated the
relationship between bond strength vs. hole diameter as well as the effect of
increasing the embedment depth while hole diameter remained constant. The basalt
blocks used had a Youngβs Modulus of 27.6 GPa and a UCS of 133 MPa. The
results exhibited mean bond strength of 7.73 MPa with a standard deviation of only
0.187 and all results showed a linear distribution dependant on bond area.
1.1.5. Bonded Chemical Anchors in Concrete
Failure of bonded anchor in concrete can occur in a variety of mechanisms (Cook et
al. (1998)) as shown in Figure 1-7 below.
Figure 1-7 - Failure methods of bonded anchors (Eligehausen et al. (2006))
Eligehausen et al. (2006) state that load displacement behaviour of single bonded
tension anchors is dependent on the stiffness and adhesion of the mortar. A well
selected mortar can result in elastic behaviour nearly to failure.
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Pull-out failure is dependent on the magnitude of the load, bond strength of the
mortar and the embedment depth. Failure can occur at the concrete/ mortar bond,
steel / mortar bond or a combination of the two. Spieth and Eligehausen (2002)
showed the drilling method and subsequent roughness at the interface between the
mortar and concrete can have a significant impact on the final bond strength.
Leftover dust or residue can also have an impact on the bond strength. Meszaros and
Eligenhausen (1998) showed that insufficient cleaning of holes can lead to a 40%
reduction in bond strength with the best cleaning method being a combination of
blowing with oil free pressurised air and brushing with a wire brush up to 3 times
each. Cook et al. (1994) tested 20 different mortar products showing results of 3
products under 10 MPa, 11 products between 10 and 20 MPa and 6 above 20 MPa,
concluding that epoxy product selection is a vital factor in final bond strength, and,
each product should be tested and treated differently.
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Figure 1-8 - Bond stress-displacement curves for different drilling methods. (Eligehausen et al.
(2006))
lv = embedment depth
ds = diameter
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1.1.6. Tension Piles
Vertical piles can be used to restrain uplift loads caused by swell from expansive
soils which can result in movement of between 50 mm and 100 mm, hydrostatic
pressures exceeding downward loads, structures subject to wind or overturning and
although not an issue in Australia expansion from frost can also cause uplift in piles.
Uplift is generally resisted by providing piles that are sufficiently long to withstand
all uplift forces with shaft skin friction where:
Uplift Resistance = Shaft Area x Bond Strength
Raked piles can also be used to resist uplift but are generally used when lateral
forces are also present such as thrust blocks or in conjunction with sheet piling
retaining walls with tie rods.
Failure in tension piles can occur in two modes:
1. The pull-out of the pile from the ground mass (Slip Failure)
2. Uplift of the ground containing the piles (Cone Failure)
Depending on the subsurface type the bond strength can be calculated in different
ways. OβNeil and Reese (1989) classify each subsurface into four different
classifications and give different methodologies for the design and calculation of the
bond strength between the pile and the geo-material.
The four classifications include:
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β’ Cohesive soil [clays and plastic silts with undrained shear strength suβ€0.25
MPa]
β’ Granular soil [cohesionless geomaterial, such as sand, gravel or non-plastic
silt, with uncorrected SPT N values of 50 blows / 0.3m or less]
β’ Intermediate geomaterial [cohesive geomaterial with undrained shear
strengths, between 0.25 MPa and 2.5 MPa (equivalent to unconfined
compression strength q, between 0.5 and 5.0 MPa); or cohesion less
geomaterials with SPT N values > 50 blows / 0.3 m]
β’ Rock [highly cemented geomaterial with unconfined compression strength >
5.
Poulos and Davis (1980) and Tomlinson and Woodward (2008) give similar
equations for calculating the uplift capacity of piles in cohesive soils where:
π·π = π(π Γ π Γ π Γ πΆπͺπ)β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.Equation 1-2
ππ’ = Uplift Capacity
π = Pile diameter
π = Embedment depth
πΆπ’ = Undrained cohesion of soil
πΌ = Adhesion factor for piles in clay (varies with clay stiffness)
π = Reduction factor for uplift (varies with clay stiffness)
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1.1.7. Load Bearing Capacity Based on Settlement
Reese and OβNeil (1989) proposed a method for calculating load bearing capacity of
drilled piers based on settlement. The method was developed based on a database of
41 load tests of piles within the following ranges:
1. Shaft Diameter: d between 0.52 m to 1.2 m
2. Bell Depth: l between 4.7 to 30.5 m
3. Field standard penetration resistance N60 = 50 to 60
4. Concrete slump between 100mm to 225 mm
From this study Reese and OβNeil (1989) were able to develop the following plots
for normalised side load transfer for drilled shafts in cohesive and cohesionless soils
based on the settlement of the pile. Figures 1-9 and 1-9a show the relationship of
side friction based on settlement of the pile and can be used to find the ideal
allowable settlement for activation of skin friction.
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Figure 1-9 - Normalised side load transfer for drilled shafts in cohesive soil (Reese and OβNeil
(1989))
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Figure 1-9a - Normalised side load transfer for drilled shafts in cohesive soil (Reese and OβNeil
(1989))
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1.1.8. Drill Types and Selection
Littlejohn and Bruce (1977) give 6 criteria for the selection of drilling method.
i. The type and capacity of the anchor
ii. The nature of the rock and material mass
iii. The borehole surface roughness requirements
iv. The accessibility and topography of the site
v. The availability and suitability of the flushing medium
vi. The drilling rate
The application of the anchor and location will mean that several of the above
parameters will be predetermined or governed by the project application and
location. Given a specific project the main governing factors in anchor selection will
be a balance of time, cost and an associated level of risk.
The main drilling systems that are available include rotary, percussive and a
combination of rotary percussive drill bits. There are two types of rotary drill bit
available, drag drill bits and roller drill bits. The key difference between the two is
that a drag bit has no moving parts while a roller cone is made of a series of rolling
drill heads. The size, depth and rock type will have the greatest impact on drill
selection. Augers or drag bits are preferred in soft friable rock, percussive or
diamond drills for hole diameters less than 100 mm and rotary rollers for medium to
hard rocks 100-300 mm.
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1.1.9. Hoek-Brown Criterion
In 2007 Hoek published a history of the Hoek-Brown Criterion stating the failure
criterion was originally developed for the book Underground Excavations in Rock
for the design of underground excavations. (Hoek 2007) The relationship was
developed in an effort to provide engineering data on rock masses from geological
information. The equation was not unique however effort was taken to link
geological information and observations to Bieniawskiβs Rock Mass Rating (RMR).
The criterion was first looking at hard rock assuming that rock mass failure was
governed by the translation and rotation of rock masses separated by jointed surfaces
and that the rock mass can be treated as isotropic. The criterion was to develop the
parameters that were currently being used in engineering practice in order to allow
for input and use in software.
The equation developed by Hoek and Brown used a modified RMR value assigning
a fixed value of 10 for the groundwater rating and setting the joint orientation at 0.
The equation did not take into account that highly jointed rock masses had a zero
tensile strength.
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Giving the following
Disturbed rock masses:
ππππ
= ππ±π© (πΉπ΄πΉβπππ)ππ
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦..β¦β¦β¦β¦β¦β¦β¦.Equation 1-3
π = exp (π ππ β100)6
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.Equation 1-4
Undisturbed or interlocking rock masses:
ππππ
= exp (π ππ β100)28
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦β¦β¦β¦β¦β¦β¦.Equation 1-5
π = exp (π ππ β100)9
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦...β¦β¦β¦β¦β¦β¦.Equation 1-6
πΈ = 10((π ππ β100) 40)β β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦.............β¦β¦β¦β¦β¦β¦.Equation 1-7
mb and mi are for broken and intact rock, respectively.
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1.1.10. Rock Mass Classifications
Different methods of classifying rock masses have been in development for over a
century. The methods have been derived using case studies from civil engineering
projects and are used to gain engineering properties from geological characteristics
of information. The system used for the Hoek-Brown Criterion is the Bieniawski
(1976) Geomechanical Classification more widely know as the Rock Mass Rating
(RMR). The system has been refined over time to the 1989 version. Both systems
use six key parameters to classify a rock and find a subsequent RMR.
β’ UCS of the Rock
β’ Rock Quality Designation (RQD)
β’ Spacing of discontinuities
β’ Condition of discontinuities
β’ Groundwater
β’ Orientation of discontinuities
Each of the parameters is presented in a table and based on these a RMR can be
defined for an area.
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Table 1-1 - Rock Mass Rating (after Bieniawski 1989)
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1.1.11. Mohr-Coulomb Strength Criterion
The MohrβCoulomb Strength Criterion is a linear envelope using principal stresses
from Mohrβs circle to describe the conditions under which an isotropic rock will fail.
The MohrβCoulomb Strength Criterion can be shown as a function of the major and
minor principal stresses and shear stress. Where all stresses are compressive it has
been shown that the criterion works well with rock. The Mohr-Coulomb Criterion
came from a combination of research and laboratory tests conducted separately by
both Mohr and Coulomb.
The shear strength of Mohr-Coulomb materials can be expressed in terms of the
cohesion of the material and the internal friction angle.
π = π + πβ² tanπβ¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦...β¦β¦β¦β¦β¦β¦.Equation 1-8
Ο = total normal stress; Ο = shear strength; Ο = effective internal friction angle c = effective cohesive strength
For a planar, clean fracture of intact rock the cohesion will be zero and the shear
strength will be determined solely by the friction angle Wylie (1992). The friction
angle will vary depending on the type of rock and site conditions. Wylie (1992)
categorises the rocks into 3 main groups including: Low friction rocks with a
friction angle between 20 to 27 degrees including schists, shale and marl. Medium
friction rocks with a friction angle between 27 to 34 degrees including sandstone,
siltstone, chalk, gneiss and slate. High friction rocks with a friction angle between
34 to 40 degrees including basalt, granite, limestone and conglomerates.
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Ο = total normal stress; Ο = shear strength; Ο = effective internal friction angle c = effective cohesive strength
π = π + πβ² tanπ
Figure 1-6 - Mohr-Coulomb Criterion
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1.1.12. Deflection Limits of Transmission Poles
Cable guys can be used to control deflection or movement of transmission poles. AS/NZS
7000: 2010 recommends that the maximum deflection of a pole at serviceability loads shall
be 5% of the poles height above ground and the βdeflection shall be limited to a value that
ensures the electrical clearances will not be infringed. This condition may also be used as an
upper limit for cracking criteria in pre-stressed concrete poles.
In most cases this make deflection not a critical factor but where there are line crossings
deflection can govern the required strength of the pole to maintain safe electrical clearances
including phase to phase and phase to ground with clearance distances ranging between
0.2m and 5.2m (Table 3.1 AS/NZS 7000: 2010.)
In areas where there are tight clearances controlling the displacement of guy foundations
can become important.
Figure 1-11 - Clearances for Unattached Crossing (AS/NZS 7000: 2010)
37
2. Existing Tension Foundation Systems
There are many types of foundations available for anchoring tension cables
including:
β’ Dead Man Anchors
β’ Drilled Shaft Piles
β’ Helical Piles
β’ Rock Anchors
The above foundation options can provide sufficient load capacity to resist the
imposed uplift on a structure each with their own advantages and disadvantages.
The was on the Elaine Terminal Station Transmission Line was to find a
methodology that would be suitable in all locations as the geotechnical
investigations showed hard rock at varying depths from 1 m to over 7 m with poor
access in many of the locations. This made it problematic to find one solution that
would work at all stay locations.
2.1. Dead Man Anchors
Dead man anchors use mass of concrete or bed logs combined with bearing on
backfill or pure mass in excavated pits to resist uplift. Dead man anchors were
originally proposed for use as foundations for the cable stays on the Elaine Terminal
Station Transmission Line. The access conditions and areas with high rock would
have made the installation of dead man anchors at the stay locations very expensive
38
and produced large amounts of waste and spoil that would have to be removed. At
some remote poles located near the edges of valleys the installation of dead man
anchors at the required angle would have been impossible. Using a unit weight of
concrete of 2400 kg/m3 a cable stay with a 200 kN load would require a mass of
concrete over 8 m3 and produced the same amount of spoil.
Concrete Dead Man Anchor
Figure 2-1 - Dead Man Anchor
39
2.2. Bored Concrete Piles
Bored concrete piles use skin friction to resist uplift and can be calculated using
equations given by Poulos and Davis (1980) or Tomlinson and Woodward (2008).
Bored piles are replacement piles and create spoil that requires disposal as well as
access for concrete trucks and reinforcement delivery. While bored piles could have
provide the required capacity within acceptable deflection limits on the Elaine
Terminal Station Transmission Line limited access at many of the pole locations and
high rock in many of the areas would have made it an expensive process. To resist a
cable stay load of 200 kN in the clay experienced in the region using a Cu of 50 kPa
a 600mm bored pile would need to reach a depth of almost 5 m creating 1.5 m3 of
spoil and require the same quantity of 32 MPa concrete.
40
Figure 2-2 - Axial Capacity of Bored Pile (Tomlinson, M and Woodward, J (2008))
Axial Capacity Calculation in Clay
ππ’ = π(π Γ π Γ π Γ πΌπΆπ’)β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦...β¦β¦β¦β¦β¦β¦.Equation
2-1
ππ’ = Uplift Capacity
π = Pile diameter
π = Embedment depth
πΆπ’ = Undrained cohesion of soil
πΌ = Adhesion factor for piles in clay (varies with clay stiffness)
π = Reduction factor for uplift (varies with clay stiffness)
41
2.3. Helical Screw Piles
Helical screw piles use a combination of skin friction on the shaft and bearing
resistance from large helical plates welded to the shaft. Helical screw piles are
replacement piles and are installed using a rotary motor. The use of a rotary motor
attached to an excavator means they can be installed quickly and efficiently in areas
with poor access and that they produce no spoil. Screw piles however cannot
penetrate through hard or medium hard rock meaning that on the Elaine Terminal
Station Transmission Line screw piles alone would not be suitable.
Pu
Uplift Bearing
Skin Friction
Figure 2-2 - Uplift Capacity of Screw Pile
42
2.4. Rock Anchors
There are 2 main types of rock bolts readily available and used in industry each with
their own advantages and disadvantages and including a variety of mechanical and
bonded rock bolts. Each rock bolt system is quite similar with a bored hole being
drilled and filled with the chosen rock bolt system. Environmental issues and
functionality are the key factors in determining which system should be adopted.
Typical applications of rock anchors include anchoring of roof or rock formations to
protect roadways or tunnels from collapse, permanent tie downs to resist overturning
and anchors to support tensioned cables.
Rock anchors are suitable in areas with hard rock preferably close to the surface and
can be installed where access conditions are poor from tracked machinery. Although
rock anchors are a form of replacement anchor their small diameter means they can
be installed with minimal spoil created. Rock anchors would have been suitable for
use on the Elaine Terminal Station Transmission Line at many of the cable stay
locations but at some locations, however no rock was encountered at depths beyond
7 m which would require expensive casings and made rock anchors alone not a
suitable anchor type.
43
Rock bolt systems include:
Mechanical/ Expansive Rock Bolts
Figure 2-4 - Expansive Shell Rock Bolt
44
Cement Grouted Rock Bolts
Figure 2-5 - Cement Grouted Rock Bolt
45
Polyester Resin/Epoxy Grouted Rock Bolts
Figure 2-6 - Epoxy/Resin Grouted Rock Bolt
46
2.5. Summary of Cable Stay Foundation Suitability
The research work presented in this thesis used the construction of the Elaine
Terminal Station Transmission Line as the case study for the development of a new
type of anchored screw pile. It can be demonstrated that at the location where Elaine
Terminal Station Transmission Line was to be constructed one foundation
methodology alone would not be suitable. This convinced the construction team to
use a new type of anchored screw pile, which provided the opportunity to conduct
the research, and testing reported in this thesis.
The suitability of the site for various types of piles has been summarised in Table 2-
1 below.
Table 2-1 Suitability of Existing Foundations
Access Ground
Water Clay / Sand Hard Rock
Dead Man Anchor Not Suitable Not Ideal Suitable Not Ideal
Bored Pile Not Suitable Not Ideal Suitable Not Ideal
Screw Pile Suitable Suitable Suitable Not Suitable
Rock Anchor Suitable Not Ideal Not Suitable Suitable
Not Suitable
Not Ideal
Suitable
The results summarised in Table 1 show that no one option would be able to provide
a solution and suitable foundation for the cable stays at the site considered as there
47
was poor access at a majority of the pole locations and the geotechnical
investigations showed areas with rock at only 1 m from the surface and other areas
with only Clay to depths of up to and beyond 7 m with groundwater likely to be
present beyond 4 m.
2.6. Outline
The thesis is comprised of three sections:
The first section details the research into previous foundation systems, anchors,
piles, rock mechanics and rock bolts. The development of the Epoxy Anchored
Screw Pile came from a combination of many of these theories and existing
products.
The second section recounts the development of the installation methodology and
the testing of the Epoxy Anchored Screw Pile, including methods for calculating the
projected capacity, as well as full details of the testing. Full-scale tests were
conducted on both the screw pile and the Epoxy Anchored Screw Pile at various
depths. The results demonstrate that the Epoxy Anchored Screw Pile had sufficient
capacity to resist the loads applied and lead to a conclusion that given the limited
cost increase of the Epoxy Anchored Screw Pile it as an effective method of
foundation.
The final section concludes this masters thesis and makes recommendations for
future development and application of the Epoxy Anchored Screw Pile.
48
3. Innovative Epoxy Anchored Screw Pile and
Installation Methodology
This research project is to explore the development of the innovative Epoxy
Anchored Screw Pile. The Epoxy Anchored Screw Pile allows screw piles to
become a viable stand-alone foundation solution in all ground conditions by adding
an epoxied socket where the screw pile reaches early refusal on rock without
attaining the required capacity. The installation methodology and test results show
that the Epoxy Anchored Screw Pile can be installed efficiently and provide an
increase in the required tensile capacity. The installation of the Epoxy Anchored
Screw Pile required only a small amount of additional equipment and the use of a
fast setting epoxy meant that they were ready to be loaded in just days and allowed
for the timely completion that was ideal for the transmission line for which it was
used. The addition of an epoxy socket significantly reduces the displacement at the
head of the screw pile.
The Epoxy Anchored Screw Pile comprises of a screw pile that is installed to refusal
on rock. If the screw pile does not reach the required capacity a socket was drilled
into the rock using a standard rotary hammer drill with an extension and a ReidbarTM
was bonded to the rock using an epoxy before both the ReidbarTM and the screw pile
were joined via a bolted and welded capping plate. ReidbarTM is a continuously
threaded grade 500N (500MPa) steel deformed bar.
The Epoxy Anchored Screw Pile was developed for use on The Elaine Terminal
Station Transmission Line which is a 132 kV line that runs between the Mount
49
Mercer Wind Farm and the Elaine Terminal Station. It provides 131 Megawatts to
the grid which is enough energy to power the city of Ballarat located in the west side
of Victoria in Australia.
29 Stay Anchors were required for the 161 Poles on the Elaine Terminal Station
Transmission Line.
Traditionally large excavations and dead man anchors have been used to support
tension loads of this nature and scale This process is slow, expensive and the
topography of the transmission line route makes it infeasible in many of the required
locations.
Screw piles were proposed as a cost effective alternative to the dead man anchors as
they can be installed in areas of limited access and produce no spoil. But at several
locations the geotechnical investigations showed that the rock was basalt at depths
as small as 1.5 m. These site conditions meant that screw piles would not be able to
penetrate to a depth to achieve the required tensile capacity with acceptable
displacements.
At the locations where the screw pile reached early refusal (less than 3m) on rock
the Epoxy Anchored Screw Pile was installed. Of the 29 anchors, 13 reached early
refusal and an epoxy screw anchor was required. All tests conducted showed very
small displacement (<1.5mm) at the required working load.
50
Rock (Basalt) Epoxy
Screw Pile
ReidbarTM and Capping Plate
Figure 3-1 - Details of Innovative Epoxy Anchored Screw Pile
51
3.1. List of Material to be installed
β’ Screw Pile β 168.3 mm Shaft Diameter with 400 mm Diameter Single Helix
β’ Threaded Reinforcement Bar (Galvanised) β 25 mm and 32 mm Diameter
ReidbarTM
β’ MKT Type V Epoxy
β’ Top Capping Plate
52
Figure 3-2 - Screw Pile
53
Figure 3-3 - Capping Plate
54
Figure 3-2 - Screw Pile Delivery
55
3.2. Equipment needed for the Installation
β’ Metabo ASR35M Dust Extractor
β’ Metabo MHE96 SDS Max Impact Drill
β’ Angle Grinder (To cut threaded bar)
β’ Electrical Generator
β’ 3 m Drill Extension
β’ 15 mm Orange Electrical Conduit (For Vacuum Extension and to Guide
Epoxy Hose)
β’ Cleaning Brush
β’ Epoxy (Including Mixing Nozzle)
β’ Clear 10 mm Extension Hose
β’ Electrical Tape and Duct Tape
β’ Tape Measure
β’ Plastic
β’ Cleaning Bucket, Water and Rags
β’ Hose Clamp
β’ Welding Equipment
β’ Test Rig
β’ Excavator
56
Drill Selection for Epoxy Anchored Screw Pile
The drill selection for use in the epoxy anchored screw anchor was based on similar
parameters to those listed by Littlejohn and Brue (1977). As the required
embedment was less than 500 mm with a 40 mm diameter rotary percussive drilling
was selected as the preferred method. Tubular steel extensions were fabricated and a
standard 40 mm Hilti drill bit selected. A steel extension was heat shrunk to the drill
bit with a total length of 3 m. The use of readily available materials meant the drill
and extension could be made quickly and attached to a standard SDS max hammer
drill. Limiting the size of all equipment means that the drilling applications are
suitable when site access is very limited and with minimal training. The drilling
process requires no large plant and is a very cost effective method for socketing the
screw pile and providing an increased tensile capacity.
Figure 3-5 - Drill with extended drill bit
57
Figure 3-6 - Head of drill head heat shrunk to extension
58
3.3. Method
3.3.1. Test Installation
As the base of the screw pile would not be visible during the installation of the
epoxy anchor the drilling equipment was tested on some rocks at the surface. The
drill was setup using the fabricated drill extension. The drill was set to a percussive
setting and the drilling was completed using percussive drilling with no flushing
medium being used. The flights on the drill bit remove any debris from the drill hole
and allow the percussive action of the drill to break through the rock.
The debris / drill residue from the rock can be seen in the photo below (Figure 3-7).
It is also evident that the unweathered rock leaves a neat penetration. The rate at
which the drill advanced and the rate of the drill was monitored by the crew drilling
the anchors to help gauge the quality of the rock in the field. In the unweathered
basalt the drilling was quite heavy and the advancement was seen to be quite slow.
59
Figure 3-7 - Drilling of test hole
60
Once the drilling of the test hole was completed to 200 mm the hole was cleaned
using a dust extractor and a cleaning brush. The cleaning process was rigorous and
included repeated sequences of brushing and vacuuming any debris from the hole.
As the cleaning would be conducted at the bottom of the screw pile the cleaning
brush was revised and the brush was attached to a PVC pipe and connected to the
vacuum. The cleaning of the hole was conducted by inserting the brush and vacuum
in a rotary motion until no more debris could be seen entering the vacuum. This
process could take up to 10 minutes. Adequate cleaning of the hole removes any
debris that can interfere with the bond between the epoxy and the basalt. Meszaros
and Eligenhausen (1998) showed that insufficient cleaning of holes could lead to a
40% reduction in bond strength.
Figure 3-8 - Cleaning of test hole
61
Figure 3-9 - Revised cleaning brush and vacuum
62
Figure 3-10 - Cleaning brush and vacuum attachment
63
Once the hole had been cleaned the epoxy and test anchor could be installed. A
standard mixing nozzle was used for the epoxy in conjunction with an extension
hose. The first injection of the epoxy was disposed as per the manufacturers
instruction prior to the extension hose being connected. It was found that beyond a
length of 1 m of extension hose, a hose clamp was required to ensure the extension
hose remained attached during the delivery of the epoxy.
Figure 3-11 - Cleaning Motion
64
Figure 3-12 - Short hose extension
Figure 3-13 - Anchor installation motion
65
The anchor stud must be cut at a 45-degree angle before being inserted into the wet
epoxy. The anchor is cut at 45 degrees and inserted with a slow twisting action to
evenly distribute the epoxy. This removes any piston action and the possibility of
any air bubbles forming and damaging the epoxy steel or epoxy rock bond. Once the
test anchor had been installed it was secured to ensure it did not move during the
curing process and left to cure. This was the end of the test installation and showed
that the drilling equipment was suitable to be used in the field for the installation of
the other stay anchors.
Figure 3-14 - Test anchor installed
66
Figure 3-15 - Drilling of test hole
67
3.3.2. Epoxy Anchor Installation Method
Step 1 β Install Screw Pile
This step was completed by SFL Piletech who are an experienced piling contractor
who operating within Australia. The screw pile was installed using an excavator
mounted rotary motor and extension arm. A Bosch DNM60L digital level was used
to install the pile at the correct angle for the cable stay. The installation of the screw
pile using a large excavator will generate sufficient force to penetrate through any
severely weathered rock but not solid rock.
In locations where screw piles were installed but reached early refusal on rock at
depths insufficient to reach the required tensile capacity the addition of a chemically
epoxied bar was socketed into the rock to help achieve the required tensile capacity.
The screw pile had an internal sleeve that acted as a guide to support the drill during
the drilling of the rock that the pile refused on. During the installation the screw pile
will also penetrate through any soft weathered rock and help to guarantee that the
rock is unweathered and a suitable material for strong bonding of the epoxy.
In total screw piles were installed at 29 locations. The final depth of the screw piles
on the project varied from 1 m to 9 m in depth with final installation torques ranging
between 24000 N-m to 45000 N-m.
68
Figure 3-16 β Screw Pile after installation
Figure 3-17 β Screw Pile after installation
Figures 3-16 and 3-17 above show images of the screw pile after installation but prior to
the installation of the epoxy anchor. In areas where the anchor was not installed
immediatly the piles were covered to prevent contamination or water entering the pile and
help to givethe best possible result. Figure 3-16 shows the pile has been extended using a
bolted flange.
69
Figure 3-18 - Bosch digital level used to check pile angle
70
Figure 3-19 - Excavator Installing Screw Pile
71
Step 2 β Site Set-Up and Initial Assessment
The drilling equipment was lightweight and only a light vehicle was required to
carry the equipment. The crew for installing the anchor included one engineer and
two workers.
Access gates for each location were marked and numbered. Once at the pole location
the equipment was unloaded and if required a crate was used to give a level surface
for the drilling team to work from.
The screw pile was examined and the depth to the bottom of screw pile was
recorded. The base of the screw pile was examined using a borescope, a steel rod
and a torch. This allowed a datum to be set up at the screw pile cut-off level and the
depth to rock was recorded. The investigation and probing also allowed us to
confirm what material the pile had refused on and the depth and properties of the
clay in the area. Field tests were done on the clay using a pocket penetrometer.
72
Figure 3-20 - Timber being used to provide level ground to work from
73
Figure 3-21 - Pocket penetrometer tests on clay
74
Step 3 β Vacuuming, Cleaning and Drilling
Once some initial measuring and setup was conducted cleaning and drilling
commenced. Initially the drilling involves removing any soft material or clay that
was caught at the bottom of the screw pile during the installation of the screw pile
but above the rock it refused on. Generally we found there was 100-200 mm of soft
material above the layer of rock that the screw pile refused on.
Drilling was conducted using rotary percussive drilling and the type of spoil, rate of
advancement and ease of drilling was used to gauge and monitor the strata and
strength of rock that was being drilled. Any change in strata was recorded on a field
check sheet and spoil was photographed, recorded and collected.
The use of handheld drill versus a machine mounted drill meant that it was possible
to gain information about the quality of rock being drilled by accessing the
difficulty/ force required to secure the drill during drilling. In some areas the initial
drilling had much less resistance than at other locations where the difficulty of
drilling was similar to that experienced when drilling the test hole. At these
locations the depth of embedment was recorded as the depth in the harder to drill
rock. While the information gained from this may not be as reliable as an intact core
sample, all tests conducted on the anchors showed that the required bond strength
and rock strength was achieved. Any change in difficulty drilling was recorded and
the drill bit was removed to check and record if the type of rock had changed. This
assessment was made by looking at the type of spoil material on the drill flights.
75
This examination gave confidence in the use of a shallow epoxy socket less than that
suggested in AS 4678 β 2002. All tests confirmed the depth was sufficient.
DCP tests were conducted in the surrounding areas of the screw pile location to
ensure that the depth of rock was consistent in the area and that the screw pile had
not refused on a floating rock. The risk of floating rocks was also overcome by
offsetting the location of the screw pile during installation.
During the drilling process it is important to remove the drill after every 100 mm
and vacuum or remove any spoil that is building up in the hole or on the flights of
the drill. Removing spoil ensures that the percussive action of the drill is breaking
the rock and increases the speed and efficiency of the drilling. The drilling and
cleaning process was continued until the required depth of rock drilled has been
achieved. Once the required depth has been achieved a final clean of the hole was
completed.
The cleaning and vacuuming process required at least 5 minutes of cleaning. As we
were unable to see inside the hole it was important to use other senses to gauge how
clean the hole was. Once finished, the brush was cleaned and reinserted like a
dipstick to ensure all loose material had been removed. If the brush was still dusty
cleaning continued.
The goal of the cleaning is to remove any loose material that may later break free
and contaminate the drill hole and destroy the bond between the rock and epoxy.
76
This requires rigorous brushing and can take up to 5 minutes or until no more dust
or debris was being removed.
A borescope and torch was used to view the hole that had been drilled into the basalt
rock. A clean hole could be seen in the borescope however it was difficult to tell
when changes in the drilling rate were seen. This amplified the importance of
recording data during the drilling.
77
Figure 3-22 - Borescope image showing cutting in basalt rock
78
Images of drilling
Final required depth
marked on drill
Figure 3-23 - Required depth
marked on drill extension
Figure 3-24 - Drilling of anchor
Figure 3-25 - Spoil from drill flights
79
Images of cleaning
Figure 3-26 - Cleaning brush
80
Figure 3-27- Cleaning base using vacuum
Figure 3-28 - Cleaning base using vacuum
Torch
81
Step 4 β Epoxy Application
After the Hole was cleaned the epoxy was inserted using a clear 10 mm hose
extension attached to an external orange electrical conduit for added support and to
ensure the epoxy is being delivered to the correct location. The stiff electrical
conduit ensured the epoxy was being delivered to the bottom of the bored hole
where required. Prior to inserting the conduit it was measured and marked to ensure
the epoxy was being delivered to the correct depth. The connection between the hose
and conduit at the bottom of the hose was taped and closed off to ensure no epoxy
was going up the conduit.
The quantity of epoxy required was calculated using the volume of the hole and this
was the minimum amount of epoxy that was distributed to the penetration at the
base of the screw pile. The hose was slowly withdrawn from the screw pile base
while the epoxy was being installed.
The epoxy was delivered using an electric gun, as the depth that the epoxy was
being delivered would be too difficult to attain with a hand held caulking gun. At the
full depth of 3 m the electric gun was only just able to deliver enough pressure, it
would be recommended that if a greater depth is required a pneumatic gun be used
or a larger hose. We experienced several issues with the pressure of the pump
blowing the hose off the nozzle. This was affixed by the introduction of a hose
clamp.
82
Figure 3-29 β Epoxy delivery hose
Figure 3-30 β Installation of epoxy
The first three trigger pulls were discarded until the colour becomes a consistent red
and then attached the mixing nozzle to the delivery hose extension. A garbage bag
was used at each location to dispose of any waste. To maintain the natural
environment any spill of epoxy to the ground was cleaned using a shovel and
disposed of in a chemical bin.
Note: The first 3 trigger pulls of the epoxy will not be properly mixed and will not
cure. Therefore it was important to ensure no unmixed epoxy goes in the extended
delivery hose.
Once removed, the extended hose can be cleaned using a wet rag and water or
discarded.
Cleaning must be done with water only. The use of detergent can contaminate the
epoxy.
83
Step 5 β Install Anchor Rod
Once the epoxy had been installed the ReidbarTM could be installed. The base of the
bar was cut at 45 degrees using an angle grinder and the bar was cleaned using a wet
rag.
The anchor stud was cut at a 45-degree angle before being inserted with a slow
twisting action to evenly distribute the epoxy. This removes any piston action and
the possibility of any air bubbles forming and damaging the epoxy steel or epoxy
rock bond.
Prior to inserting the bar it was measured and the top of pile cut-off level was
marked on the bar to ensure that full embedment in the epoxy was achieved. The
bar was inserted using a slow twisting action to reduce the risk of voids forming in
the epoxy and guarantee the best bond between the rock, steel and epoxy. Once the
rod had been inserted the top of the screw pile was covered so no debris could enter
the opening at the top.
The size of ReidbarTM varied depending on the required tensile strength and both 25
mm and 32 mm diameter ReidbarTM was used.
84
Figure 3-31 β Install Anchor with slow twisting action
Figure 3-32 β Base of ReidbarTM cut at 45 degrees
85
Figure 3-33 - Anchor Installed and covered to avoid contamination
86
Step 10 β Welding Junction Plate
Once testing had been completed the junction plate was screwed to the ReidbarTM
and welded to the top of the screw pile. A free pin and bolt was connected to the
stay of the transmission pole that could then be tightened to engage the Epoxy
Anchored Screw Pile.
Figure 34 - Junction Plate Welded to Pile
87
Figure 3-35 - Details of Junction Plate
Figure 3-35 above shows the dimension and details of the junction plate that was
used. The plate used connects the top of the screw pile with the anchor rod and
eliminate the risk of any momentous energy developing as the stay remains in
tension at all times.
88
Step 11β Inspection of Epoxy Anchored Screw Piles
Six months after the connection and loading of the Epoxy Anchored Screw Pile an
on-site inspection of the cable stays was conducted to make sure that there was
tension in the cables and to ensure the capacity was sufficient. This inspection
showed that there was tension in the stays and hence it was possible to again
confirm that the anchor capacity was sufficient.
Figure 3-36 - Inspection of Anchor Stay
Figure 3-37 - Junction Plate
89
3.3.3. Issues Encountered During Anchor Installation
This section details the installation at the anchors at various locations and any issues
that were encountered and how they were overcome.
Issues Encountered
Issue 1. Screw Guide Not Installed
At two locations the internal guide seen below was not installed in the screw pile.
The lack of internal guide meant that the depth of topsoil and clay above the rock
increased to 600 mm as compared to 100mm-200 mm at other locations where the
guide was installed. The lack of internal guide also made the drilling of the basalt
that the pile refused on very difficult.
To ensure that the drilling could take place without the guide the 600 mm of topsoil
and clay was removed using a petrol earth auger with a 100 mm auger. This
however left a large void and it was too difficult to secure the drill and extension to
drill the basalt. To enable drilling a steel circular hollow section (CHS) with an
internal diameter of 50 mm was driven into the last 150 mm of clay at the base of
the pile and it was cleaned using the drill extension. Once the clay had been
removed the CHS was secured and the drilling of the rock could begin. Where the
guide was not installed the drilling took significantly longer as it was difficult to
begin the drilling.
90
Figure 3-38 - Screw Pile with internal guide
91
Figure 3-39 - Torch used to examine screw pile with no internal guide
92
CHS to guide drill
Figure 3-40 - Screw Pile without internal guide but with CHS to guide drill bit.
Figure 3-41 - Petrol Auger
93
Issue 2. Changes in drill advancement and drilling through rock.
The Anchor at Pole 25 showed unique ground conditions. The drilling was a little
inconsistent, initially hard rock was encountered that was typical to the other
locations but at small intervals between 50-100mm the ease of drilling changed.
This was indicative of different layers / classes of rock which differentiated the
ground conditions for Pole 25 from those for the other poles. The advancement of
the drill and spoil on the flights was used to assess the weathering of the rock. The
spoil on the flights of the drill was very consistent, which indicated that the level of
weathering in that area was more significant than in other areas or that the drill was
passing from areas of crystalline massive rock to areas of vesicular porous material. DCP
tests were conducted in the surrounding area to ensure that the screw pile had not been
obstructed by a floating rock. The DCP refused at the same depth as the screw pile showing
that the pile had refused on a shelf of rock. Because of the inconsistencies the total
embedment depth at pole 25 was increased. It was tested and under the 75% proof
load the movement experienced was less than 0.6mm.
Issue 3. No rock encountered at base of screw pile.
Drilling at one anchor showed the screw pile did not refuse on rock. The screw-
piling contractor returned and was able to install the screw pile to a depth beyond
3m that did not require an epoxy anchor. This issue flagged that while high torque
values were being recorded the pile did not actually refuse on rock and that it was
likely an obstruction such as a tree root.
94
4. Test Details of the new Epoxy Anchored
Screw Pile Tests were conducted on five of the twelve Epoxy Anchored Screw Piles that were
installed. The data was only recorded for four of the five tests. These tests were
conducted to exceed the working load at each stay location to verify the system. As
failure of a cable stay would lead to increased sag in the power line, deflection of the
pole is of extreme importance. The tests were conducted to verify the stiffness. Once
the cables were installed the pole line was inspected regularly during the
construction phase and a final visual inspection of the anchors was conducted six
months after the completion of construction.
A single 60 ton jack was used to carry out the short-term tension load test. The jack
sits above a spreader beam atop the Epoxy Anchored Screw Pile. The beam was
supported on two reaction points comprising of timbers to transfer the compression
loads on its ends. The timbers allow for the beam and jack to be positioned in the
correct angle to allow for testing of the Epoxy Anchored Screw Pile.
Tests that were conducted on the screw pile only were conducted on temporary piles
vertically and two reaction piles were used to support the spreader beam rather than
timbers.
The spreader beam was used to allow for the testing of the whole system as a jack
atop the pile would only test the epoxy bond and it was likely that failure would also
occur in the form of rock cone failure, with steel failures being very unlikely at the
required loads.
95
The spreader beam selected comprised of two 360mm deep universal beams welded
together with a central hole to allow for the connection of the jack. We selected this
size beam so that under the test load there would be minimal deflection that would
render our results inaccurate.
Deflection of Spreader Beam
Figure 4-1 - Deflection of Spreader Beam
πΉπππ = π· Γ ππ
πππ¬π°= π.πππ ππβ¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦ β¦Equation 4-1
π = 200,000 π
π = 4000 ππ
πΈππ‘πππ = 200 πΊππ
πΌ360ππ΅57(2) = 2 Γ 161 Γ 106 = 322 Γ 106 ππ4
The load was applied incrementally and each load was held for 5 minutes before
being increased. Once the maximum load was obtained the load was again decreased
incrementally and the displacement of the pile was recorded. If the testing procedure
was undertaken again it would be recommended that the pile was loaded a second
P
96
time and the change in final settlement was recorded to better gauge the permanent
movement.
All tests were monitored and the pile head displacements and the test pressures on
the calibrated pump were recorded. The pile head displacements were measured
using dial gauges to the nearest 1/100th of a millimetre. Loads were increased
incrementally in two stages, loading to 75% of the ultimate load and unloading back
to zero in accordance to the Australian Piling Code AS2159:2009
97
Details of the test rig setup can be seen in below:
Figure 4-2 - Test Rig Details
98
Figure 4-3 - Test Rig Setup
99
Figure 4-3 - Testing of Screw Pile
60t Jack
60t Jack and Power pack
Calibrated Gauge
100
Figure 4-4 - Testing Screw Pile
Spreader Beam
Reaction Piles
Test Pile
101
5. Estimation of the load capacity of the
Epoxy Anchored Screw Pile
5.1. Failure Mechanisms
The failure mechanisms can be seen in the flow chart below. While the skin friction
acting on the screw pile that encases the epoxied ReidbarTM may contribute there is
very limited movement allowed before failure in the epoxy socket will occur so that
the screw pile will not be allowed to deflect far enough to activate the skin friction.
This means that by the time the epoxy anchor fails the screw pile will likely not
contribute significantly to the total capacity of the system but will in fact act
independently and merely provide corrosion resistance to the ReidbarTM.
Flowchart of failure mechanisms
Epoxy Slip Failure Steel Bar Failure Rock Cone Failure
Screw Pile Failure
102
5.2. Screw Pile
Screw Pile capacity calculations were conducted by SFL Piletech in accordance to
AS2159-1978 and calculated by accessing the failure of a cylinder of soil above the
single bottom helix.
The following equations were used to calculate the capacity prior to the onsite
testing.
ππ π’π = π(π Γ π Γ π Γ πΌπΆπ’)β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦Equation
5-1
π π’π = Ultimate Geotechnical Uplift Capacity
π = Reduction Factor
π = Embedment depth to helix (Top 0.5m ignored)
π = Diameter of Helix
πΆπ’ = Undrained cohesion of soil
πΌ = Adhesion factor for piles in clay (varies with clay stiffness as per AS2159-
1978)
Based on the geotechnical investigations conducted onsite showing very stiff clay
with the undrained cohesion of the soil of 50 kPa and as per AS2159-1978 a πΌ of 0.9
was used.
The helix diameter of all piles was 400mm and a π = 0.6 was adopted.
Based on these values the below table shows the capacity the screw pile achieved at
varying depths.
103
Calculations for screw pile capacity can be seen in the table below, based on the
values shown.
ππ π’π = π(π Γ π Γ π Γ πΌπΆπ’)β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦Equation
5-2
π = Reduction Factor = 0.6
π = Embedment depth to helix (Top 0.5m ignored) = Depth
π = Diameter of Helix = 400mm
πΆπ’ = Undrained cohesion of soil = 50kPa
πΌ = Adhesion factor for piles in clay = 0.9
Figure 5-1 - Calculated Screw Pile Capacity
0
50
100
150
200
250
0 1 2 3 4 5 6 7
Capa
city
(kN
)
Depth (m)
Calculated Screw Pile Capacity
Capacity
104
5.3. Epoxy Anchor Failure
5.3.1. Slip Failure
Slip failure of the epoxy is likely to occur at the rock / epoxy interface prior to the
steel / epoxy interface, although in concrete the epoxy can give bond strengths of up
to 25 MPa. Bond strengths for the epoxy / rock interface have come from the
recommendations given by Littlejohn and Bruce (1977) in conjunction with
engineering rock properties given by Gu et al. (2008).
Littlejohn and Bruce give ultimate bond strengths in basalt between 5.73 to 6.37
MPa recommending a factor of safety between 1.5 and 4 depending on rock quality.
These values are quite conservative to account for the unknown factors that are
present when drilling into rock. Studies done by A Kilic et al. (2002) showed bend
strength with cementitious grouts and basalt with mean bond strengths of 7.73 MPa.
105
Table 5-1 β Engineering Properties of basalt (Gu et al. (2008))
Rock Type
Weathering
Grade Moisture Content (%) qu (Mpa) n (E/qu) E (Mpa)
Basalt
EW-HW >11 4 100 400
HW 9 - 11 10 120 1250
HW-MW 7 - 9 25 160 4000
MW 5 - 7 50 200 10000
MW-SW 3 - 5 90 250 22500
SW 1 - 3 150 300 45000
SW-FR <1 250 400 100000
106
Boreholes from the installation of the electrical poles exposed rock samples that
allowed for assessment of the basalt at each location to be evaluated. Samples that
were still intact from coring showed at the depths the screw pile was refusing the
level of weathering was quite low and the UCS of the basalt was greater than 100
MPa.
The ultimate bond strength of the epoxy anchor can be calculated with the following
equation. Values for the Ultimate bond strength given by Littlejohn and Bruce
(1977) have been used to give a projected capacity of the epoxy.
π· = π Γπ ΓπΓπͺπ
β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦..β¦β¦β¦β¦β¦β¦β¦β¦..β¦β¦Equation 5-3
π = Capacity
π = Diameter
π = Length
πΆ = Bond Strength
π = Factor of Safety
107
Figure 5-2 β Projected Epoxy Bond Strength
**Bond strengths used are 1.43 and 4.24MPa, values from this table should be used as a guideline and should be verified with field investigations with
acceptable deflection limits.
The anchors were tested to the working load or 75% or the ultimate load and results
from these tests showed displacements less than 1.5mm in all locations.
0
100
200
300
400
500
600
0 0.2 0.4 0.6 0.8 1
Capa
city
(kN
)
Epoxy Embedment Depth
Projected Epoxy Bond Strength - 40mm Diameter
Minimum Projected BondStrength
Maximum Projected BondStrength
108
Figure 5-3 - Rock sample from drilling poles
Figure 5-4 - Rock sample from drilling poles
109
5.3.2. Cone Failure
As the field investigations showed good to very good rock cone failure will take
place at one of two locations depending on the level of weathering and degree of
fissure in the rock mass. For a rock mass that is soft, weathered and heavily fissured
the failure cone will be at 60 degrees and occur at the midway point of the bond and
for other rock with limited weathering or fissures failure will occur at the base of the
anchor at an angle of 90 degrees.
Figure 5-5 β Cone failure location for good rock
Figure 5-6 - Cone failure location for poor rock
110
The capacity of the rock cone in good to very good rock can be calculated using the
tensile strength of the rock mass and the area of the failure cone using the following
equation which ignores the mass of the rock.
Figure 5-5 - Cone Failure
πΈ = πππΓπ Γπ³π
πππππ½ΓππΊβ¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦β¦β¦β¦β¦β¦β¦β¦Equation 5-4
π = Capacity
πΏ = Cone Length
ππ‘π = Tensile Strength of rock mass
π = Angle of Failure
πΉπ = Factor of Safety
111
Tugrul and Gurpinar (1997) conducted testing on basalt at different levels of
weathering and gave the following Table 5 -2 gives mean UCS and tensile strengths
of basalt tested. The results from these tests can be seen in Table 5 -2 below.
Table 5-2 β UCS and Tensile Strengths of basalt
Ο Ultimate Compressive Strength (MPa)
Ο Tensile Strength (MPa)
E Youngβs Modulus (MPa)
Weathering Grade Weathering Level Min. Max. Mean Min. Max. Mean Min. Max. Mean C-I Fresh Rock 105.26 136.42 120.1 8 10 8.99 44000 57700 50127
C-IIC Moderately Weathered 30 54.95 43.03 3 5 3.86 14000 26100 20073
C-IIIB Extremely Weathered 10 23.58 15.2 0.77 2.31 1.76 10500 19000 15093
B-I Fresh Rock 86.32 120 100.15 7.69 9.23 8.49 46000 81650 66101 B-IIA Faintly Weathered 60 107.79 86.03 6.43 8.15 7.42 32000 56800 48073
B-IIC Moderately Weathered 27.37 52.63 37.71 3.11 4.77 4.01 20000 36000 28039
B-IIIA Highly Weathered 21.05 36.21 28 2 3.69 2.78 6000 21700 10800
B-IIIB Extremely Weathered 4.21 16.84 7.9 - - - - - -
A-I Fresh Rock 88.42 129.05 106.19 8.08 9.54 8.79 44000 71000 56114 A-IIB Slightly Weathered 44.21 70 58.12 5 7.08 6.13 24650 42600 36506 A-IIIA Highly Weathered 15.37 31.37 22.5 2.23 4 3.13 10000 21950 15000
A-IIIB Extremely Weathered 3.69 16.26 6.9 - - - 5065 15600 8120
112
Using the equation 5- 3 from above for the capacity of the rock cone and
conservatively using the tensile strength of highly weathered basalt and a 30 degree
cone at the midpoint to be conservative the uplift resistance of the cone will be:
πΈ = πππΓπ Γπ³π
πππππ½ΓππΊ= π.ππΓπ Γππππ
ππππππΓπ= 232 kNβ¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦β¦β¦Equation 5-5
π = Capacity
πΏ = 200 mm
ππ‘π = 2.78 MPa
π = 30
πΉπ = 2
Using the input shown above and Equation 5 -4 with a factor of safety of 2 and conservative rock
strength values it would be expected that rock cone failure would occur at 232kN.
113
5.3.3. Steel Failure
Steel Bar Failure Based on Calculations
The steel used within the anchor was Grade 500 N ReidbarTM, which has the
following properties.
Table 5-3 β Properties of ReidbarTM
Bar
Diameter
Min Yield
Stress (MPa)
Ultimate
Yield Stress
(MPa)
Minimum Shear
(.62 min ult)
(MPa)
Mass
(kg/m)
Nom
Area
25mm 245.5 265.1 164.4 3.95 491
32mm 402 434.4 269.2 6.47 804
The elongation of the ReidbarTM can be calculated using Hookeβs Law as the steel is
still in the elastic region. Using the equation:
πΉ = π·π³π¨π¬
mmβ¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦Equation 5-6
πΏ = Deflection / Elongation of Steel (mm)
π = Force (N)
πΏ = Free Length (mm)
π΄ = Cross Sectional Area (mm2)
πΈ = Youngβs Modulus
The ultimate strength of the ReidbarTM is greater than the strength of the rock mass where cone
failure occurs. Due to possible bonding at the base of the pile it is difficult to predict the elongation of
the ReidbarTM and Screw Pile.
114
Summary
Using the tables and formulas from section 5.3 the projected capacity can be
calculated. Section 5.3 shows that failure is likely to occur through either slip failure
at the epoxy rock interface or rock cone failure depending on the level of weathering
of the basalt and the calculated results give an ultimate tensile capacity upwards of
200 kN.
The ultimate bearing strength of the pile should not be greater that the tensile
strength as it may damage the bonded epoxy socket.
These conditions were qualified and tested by examining rock samples from the
drilling and spoil from the poles at the guy locations, recording the difficulty drilling
and the rate of advancement of the drill and examining the bored hole using a
borescope. The conclusion in the quality of the rock was verified by testing the
displacement at the head of the screw pile. The results show that the bond of the
epoxy and the rock strength are sufficient and the displacement at the pile head was
reduced by a factor of 10.
115
6. Test Results
6.1. Screw Pile Only
Load displacement curves can be seen for screw piles that were tested at depth
varying from 1.8 m to 3.7 m. The screw piles had the same shaft diameter of 168.3
mm with a single 400 mm diameter helix at the base of the pile.
Load test 1 was conducted on a helical screw pile installed to a depth of 1.8 m in
stiff clay before refusal on rock. The test showed limited displacement below 75 kN
increasing to a maximum of just over 35 mm at 240 kN with almost no recovery
once the load was released.
Load test 2 was conducted on a helical screw pile installed to a depth of 2.8 m
before refusal on rock. The test showed displacement of 2 mm at 80 kN but
increased to 4-5 mm at 103 kN. Once the load was released a permanent
displacement of 4 mm was not recovered. The pile was again loaded to 206 kN and
over 22 mm of displacement was recorded with a permanent displacement of 20
mm.
Load test 3 was conducted on a helical screw pile installed to a depth of 3.7 m. The
test showed limited displacement less than 2 mm up to 90 kN, once loaded to 96 kN
4 mm of displacement was experienced with a permanent displacement of 3mm. The
pile was again loaded to 125 kN where a 16 mm displacement was seen. Once the
load was released a permanent displacement of 15 mm was seen.
116
0
25
50
75
100
125
150
175
200
225
250
0 5 10 15 20 25 30 35 40
Load
(kN
)
Displacement (mm)
Load Test 1 - 1.8m Screw Pile
Figure 6-1 - Load Test 1
117
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
0 3 5 8 10 13 15 18 20 23 25
Load
(kN
)
Displacement (mm)
Load Test 2 - 2.8m Screw Pile
Figure 6-2 - Load Test 2
118
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
0 2 4 6 8 10 12 14 16 18
Load
(kN
)
Displacement (mm)
Load Test 3 - 3.7m Screw Pile
Figure 6-3 - Load Test 3
119
6.2. Epoxy Anchored Screw Pile
Load displacement curves can be seen for screw piles with the epoxied socket. The
depth into basalt varied at each location, as did the depth of screw pile. All screw
piles has a shaft diameter of 168.3 mm with a helix diameter of 400 mm at the base
of the pile. At all recorded test locations a 25 mm ReidbarTM was installed. An
additional test was conducted at Pole 147 where a 32 mm ReidbarTM was installed.
This test was successful but unfortunately no data was recorded. The pull out tests
conducted on the epoxy screw anchor showed acceptable levels of displacement
under the required working load on the pile.
The Epoxy Anchored Screw Pile was tested within the serviceability displacement
limits of AS2159-2009 with all tests being conducted to 75% of the ultimate load
using the equation
πΉπππππππππ = π·π³π¨π¬
+ π.πππ mmβ¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦β¦.Equation 6-1
πΏπππππ€ππππ = Head Displacement (mm)
π = Force (N)
πΏ = Free Length (mm)
π΄ = Cross Sectional Area (mm2)
πΈ = Youngβs Modulus
120
Table 6-1 β Summary of Epoxy Anchored Screw Pile Results
Test Number (Location) Screw Pile
Depth (m)
Depth of
Epoxy
Socket
(mm)
Test Load
(kN)
Maximum
Displacement (mm)
Allowable
Displacement (mm)
Load Test 4 (Pole 7) 1.8 450 71 1.1 1.85
Load Test 5 (Pole 25) 1.1 500 75 0.55 1.4
Load Test 6 (Pole 54) 1.5 500 112.5 0.85 2.43
Load Test 7 (Pole 46) 1.8 600 120 0.24 2.77
Load Test 8 (Pole 147) 1.5 850 126.75 **Not Recorded **Not Recorded
121
Static Load Test 4 and 5
0
10
20
30
40
50
60
70
80
0.00 0.20 0.40 0.60 0.80 1.00 1.20
Load
(kN
)
Displacement (mm)
Static Load Test 4
Figure 6-4 - Static Load Test 4
122
0
10
20
30
40
50
60
70
80
0.00 0.10 0.20 0.30 0.40 0.50 0.60
Load
(kN
)
Displacement (mm)
Static Load Test 5
Figure 6-5 - Static Load Test 5
123
Static load tests 4 and 5 shows some initial displacement that appears to be the
taking up of slack within the system. Once the initial movement occurred when
loaded beyond this point at the same rate the displacement seen was less than 0.1 β
0.2 mm. When unloaded the permanent displacement was between 0.35 and 0.7 mm
showing a recovery from the maximum displacement of 0.2 mm to 0.3 mm in each
case. In both case the displacement and permanent displacement was very small and
within the acceptable serviceability displacement limits of AS2159-2009.
124
Static Load Test 6 and 7
0
10
20
30
40
50
60
70
80
90
100
110
120
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90
Load
(kN
)
Displacement (mm)
Static Load Test 6
Figure 6-6 - Static Load Test 6
125
0
10
20
30
40
50
60
70
80
90
100
110
120
130
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Load
(kN
)
Displacement (mm)
Static Load Test 7
Figure 6-7 - Static Load Test 7
126
The results from load test 6 and 7 varied a little when compared to tests 4 and 5. In
tests 6 and 7 when the load was applied it did not appear that there was any slack in
the system and both sets of results yielded very small temporary and permanent
displacements. A gauge calibrated to record measurements in the order of 1/100 of a
millimeter was used and it can be concluded that at the working load all tests
showed acceptable amount of movement. The small displacements when compared
to the results from the screw piles without the epoxy socket showed that the epoxy /
rock bond was still intact and that rock cone failure had not occurred.
127
0
50
100
150
200
250
0 2 4 6 8 10 12 14 16 18 20 22 24
Load
(kN
)
Displacement (mm)
Load vs Displacement - Screw Pile vs Epoxy Anchored Screw Pile
Plot 4
Plot 5
Plot 6
Plot 7
Plot 1 Screw Pile Only
Plot 3 Screw Pile Only
Figure 6-8 - Combined load test results
128
Figure 6-9 - Combined load test results
0
25
50
75
100
125
150
0 2 4 6 8 10
Load
(kN
)
Displacement (mm)
Load vs Displacement - Screw Pile vs Epoxy Anchored Screw Pile
Plot 4 Plot 5 Plot 6
Plot 7 Plot 1 Screw Pile Only Plot 3 Screw Pile Only
129
The previous two charts show results from load displacement tests on the screw pile
and also the Epoxy Anchored Screw Pile. The results show that the displacements
experienced by the screw pile versus the Epoxy Anchored Screw Pile are
significantly larger at similar loads. If failure were to occur in the Epoxy Anchored
Screw Pile in either the form of rock / epoxy failure or rock cone failure it would be
expected that the displacement would be similar to that of the screw pile alone. As
this is not the case it can be concluded that this failure has not occurred and that the
basalt is not fissured and the level of weathering allows the epoxy bond to achieve
the required capacity.
130
7. Conclusions
The Epoxy Anchored Screw Pile can be used to provide additional capacity and
reduce the displacement of the screw piles that refuse on rock. The installation
method showed it is not always necessary to spend expensive resources drilling,
cutting or excavating large areas of rock to provide the required tensile capacity
within acceptable displacement limits in areas where rock with limited weathering
or fissures are present. The use of the Epoxy Anchored Screw Pile produces limited
to no spoil and allows screw piles to be a viable option in all conditions with only
the addition of some minor equipment. The use of tracked machinery to install the
screw pile makes the Epoxy Anchored Screw Pile suitable even in areas with poor
access without the need to build expensive access roads and removing the need for
heavy tired vehicles such a concrete agitators.
The use of a hand held rotary percussive drill was inexpensive, quickly implemented
and allowed for rapid installation of the epoxy socket. As shown by Spieth and
Eligehausen (2002) rotary percussive drilling gives a rough cut on the drilled hole
and increases the possible bond strength at the epoxy / rock interface. The hand held
drilling meant that it was possible to gauge the quality of the rock that the pile
refused on through monitoring the speed and difficulty in advancement. In addition
to this a soil report, DCP tests and an assessment of the spoil from the pole
installation gave confidence in the bond that would be achieved by the epoxy. This
was confirmed by the testing of the Epoxy Anchored Screw Pile. Installation of the
131
Epoxy Anchored Screw Pile was quick and the use of a fast setting epoxy allowed
for the system to be loaded after only 24 hours including testing.
The testing of the Epoxy Anchored Screw Pile was conducted at a rate of two to
three tests per day and all tests conducted showed acceptable amounts of
displacement up to 20 times less than the screw pile alone. However, if the tests had
failed due to the underlying rock being highly fissured or weathered it may have
been difficult to install a replacement anchor using the same methodology. While all
tests concluded that in the given situation the epoxy socket was sufficient, if the
process was implemented again it would be recommended that a non-situation
Epoxy Anchored Screw Pile is tested to failure. The values used to calculate the
capacity in the results section have used conservative bond strength values and Cook
et al. (1994) have shown that the epoxy concrete bond strength can be greater than
20 MPa and the Youngβs Modulus of both concrete and basalt are very similar. The
low displacements also make the Epoxy Anchored Screw Pile suitable in areas
where long term displacement under sustained load needs to be controlled and could
be used for socketing screw piles in areas of expansive soils.
Failure of the Epoxy Anchored Screw Pile would most likely be either epoxy / rock
bond failure or rock cone failure both of which are non-elastic.
The Epoxy Anchored Screw Pile provided an innovative solution for the foundations
of the cable stays on the Elaine Terminal Station Transmission Line. The installation
was quick and cost effective as it reduced the need for expensive access roads to be
constructed and the additional equipment required was procured using items that are
readily available. The short curing time means that stringing of the cables can be
conducted prior to that of concrete dead man anchor. Though not suitable in all
132
locations where appropriate the Epoxy Anchored Screw Pile makes screw piles a
valid foundation solution in a range of ground conditions where conventional screw
piles alone would not be suitable.
133
8. Recommendations
To improve the system in the future de-bonding the ReidbarTM and the screw pile
through the use of a bolted top pile instead of a welded top plate and allowing the
screw pile to move independently would allow for part of the load to be resisted by
the screw pile and reduce the load on the epoxied socket. The testing done by Reese
and OβNeil (1988) and also the testing conducted on the screw pile with the epoxy
socket showed that with only 5 mm of movement the screw pile could resist up to 75
kN and reduce the load on the epoxy socket and create better synergy between the
screw pile and epoxy socket.
It would be recommended that if future applications are adopted significant
geotechnical investigations be undertaken prior to adopting the Epoxy Anchored
Screw Pile and that prior to commitment to a full installation program a test
installation is conducted. Current bond strengths given for rock anchors are very
conservative and the development of a site-specific testing regime of the Epoxy
Anchored Screw Pile would be required. Further testing of the Epoxy Anchored
Screw Pile to failure would be very useful and help for the future development of
this application. Adapting the system to induce failure in the steel and not the
chemical bond or rock cone would allow for ductile failure of the system and can be
achieved by increasing the embedment depth and testing as required.
134
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