choi-review on the jet grouting method
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University of Southern Queensland
Faculty of Engineering and Surveying
Review of the Jet Grouting Method
A dissertation submitted by
Richard Fun Yiu CHOI
in fulfillment of the requirements of
Courses ENG4111 and 4112 Research Project
towards the degree of
Bachelor of Engineering (Civil Engineering)
Submitted: October 2005
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ABSTRACT
Jet grouting is a soil improvement technique which employs high-speed fluid jets to
erode soils. The resulting cavity is subsequently filled with grout to form a composite
material with enhanced characteristics. In a typical application, a borehole is first
drilled to the depth of the treatment strata. A nozzle located near the tip of the rod
ejects a horizontal pressurized water jet to cut into the soil. As the rod is rotated and
lifted, a cylindrical cavity forms. Grout is ejected through a lower nozzle to mix with
and displace the soil slurry, forming a columnar soilcrete element.
The purpose of this paper is to present the background behind the jet grouting tech-
nique and to review its current state of development in ground improvement. General
grouting is first discussed to provide a contextual background. Background informa-
tion on the jet grouting process is then presented, covering various aspects such as
equipment, operational parameters, quality control, etc. Finally, select case histories
illustrating the various applications and situations in which jet grouting has been used
before are presented. The contents of this paper are based on studies, case histories,
and reports from researchers and specialist contractors which have experience in thefield of jet grouting.
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University of Southern Queensland
Faculty of Engineering and Surveying
ENG4111 & ENG4112Research Project
Limitations of Use
The Council of the University of Southern Queensland, its Faculty of Engineering
and Surveying, and the staff of the University of Southern Queensland, do not accept
any responsibility for the truth, accuracy, or completeness of material containedwithin or associated with this dissertation.
Persons using all or any part of this material do so at their own risk, and not at the risk
of the Council of the University of Southern Queensland, its Faculty of Engineering
and Surveying or the staff of the University of Southern Queensland.
This dissertation reports an educational exercise and has no purpose or validity be-yond this exercise. The sole purpose of the course pair entitled Research Project isto contribute to the overall education within the students chosen degree program.
This document, the associated hardware, software, drawings, and other material set
out in the associated appendices should not be used for any other purpose: if they areso used, it is entirely at the risk of the user.
Prof. G. BakerDean
Faculty of Engineering and SurveyingLimitations of Use
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Certification
I certify that the ideas, designs and experimental work, results, analyses, and conclu-sions set out in this dissertation are entirely my own effort, except where otherwise
indicated and acknowledged.
I further certify that the work is original and has not been previously submitted for
assessment in any other course or institution, except where specifically stated.
Richard Fun Yiu CHOI
Student Number: 0050027402
Signature
Date
Certification
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TABLE OF CONTENTS
Page
Abstract......................................................................................................................... i
Limitations of Use ....................................................................................................... ii
Certification................................................................................................................iii
List of Tables ............................................................................................................ viii
List of Figures............................................................................................................. ix
List of Figures............................................................................................................. ix
Acknowledgements .................................................................................................... xi
Acknowledgements .................................................................................................... xi
1 BACKGROUND ............................................................................................. 1
1.1 Need for ground improvement.............................................................. 1
1.2 Introduction to grouting ........................................................................ 2
1.3 Development of jet grouting ................................................................. 21.4 Areas of application .............................................................................. 3
1.4.1 Mechanical property improvement ........................................... 3
1.4.2 Permeability and erosion control .............................................. 4
1.4.3 Settlement control ..................................................................... 5
1.4.4 Other applications ..................................................................... 5
1.5 Grouting methods overview.................................................................. 5
1.5.1 Grouting methods by grout type ............................................... 6
1.5.2 Grouting methods by process.................................................... 6
1.5.3 Grouting methods by mode of interaction ................................ 7
1.5.4 Other grouting methods ............................................................ 9
2 GROUTS........................................................................................................ 11
2.1 Grout classification............................................................................. 11
2.2 Grout properties .................................................................................. 12
2.3 Cement grouts ..................................................................................... 14
2.3.1 Review of Portland cements ................................................... 14
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2.3.2 Supplementary additives and admixtures ............................... 15
2.3.3 Filler materials ........................................................................ 16
2.3.4 Water-cement ratio.................................................................. 16
2.4 Chemical grouts .................................................................................. 18
2.4.1 Chemical grout systems .......................................................... 19
2.4.2 Chemical grout classification.................................................. 19
2.4.3 Chemical grout usage.............................................................. 20
2.4.4 Sodium silicates ...................................................................... 20
2.4.5 Acrylamides and acrylates ...................................................... 21
2.4.6 Lignosulfonates....................................................................... 22
2.4.7 Polyurethanes.......................................................................... 23
2.5 Groutability......................................................................................... 23
3 JET GROUTING BACKGROUND............................................................ 25
3.1 Introduction......................................................................................... 253.2 Jet grouting variants............................................................................ 27
3.2.1 Generic systems ...................................................................... 27
3.2.2 Note on historical systems ...................................................... 29
3.2.3 Subvertical jet grouting........................................................... 30
3.2.4 Multiple-stem grouting ........................................................... 30
3.3 Jet grouting notes ................................................................................ 30
3.3.1 Eroding mechanism ................................................................ 31
3.3.2 Replacement versus mixing action ......................................... 31
3.3.3 Air shroud ............................................................................... 323.3.4 Airlifting effect ....................................................................... 33
3.3.5 Volume versus pressure .......................................................... 33
3.3.6 Spoils return............................................................................ 33
3.4 Strengths and limitations..................................................................... 34
3.4.1 Improvement of physical properties ....................................... 34
3.4.2 Wide range of soil applicability.............................................. 34
3.4.3 Low space requirements ......................................................... 34
3.4.4 Minimal site disturbance......................................................... 35
3.4.5 Ability to bypass buried obstructions ..................................... 35
3.4.6 Controllability, predictability, and automation....................... 35
3.4.7 Flushing requirements............................................................. 35
3.4.8 Costs........................................................................................ 36
3.5 Developments ..................................................................................... 36
3.5.1 Super jet grouting.................................................................... 36
3.5.2 Cross jetting ............................................................................ 36
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3.5.3 Mechanical mixing and jet grouting ....................................... 37
4 JET GROUTING PRACTICE .................................................................... 38
4.1 Introduction......................................................................................... 38
4.2 Equipment ........................................................................................... 38
4.2.1 Pre-drilling versus self-jetting setups...................................... 40
4.2.2 Monitor and nozzle properties ................................................ 40
4.3 Operational parameters ....................................................................... 41
4.3.1 Fluid pressures and flow rates................................................. 42
4.3.2 Rod withdrawal and rotation rates .......................................... 43
4.3.3 Layout and sequencing ........................................................... 43
4.4 Grouting design................................................................................... 43
4.4.1 Weak soils............................................................................... 44
4.4.2 Required soil information ....................................................... 44
4.4.3 Soil testing .............................................................................. 454.4.4 Grouting trials ......................................................................... 46
4.5 Monitoring and control ....................................................................... 46
4.5.1 Grouting control...................................................................... 46
4.5.2 Verification of results ............................................................. 47
4.5.3 Monitoring of environment..................................................... 48
5 ILLUSTRATIVE APPLICATIONS........................................................... 49
5.1 Introduction......................................................................................... 49
5.2 Underpinning and support................................................................... 50
5.2.1 Quay wall stabilization works, Kingston Bridge, Glasgow.... 50
5.2.2 Excavation support for Singapore Post Center....................... 53
5.3 Tunneling ............................................................................................ 54
5.3.1 Tunnels for A43 motorway in the French Alps ...................... 55
5.4 Groundwater control ........................................................................... 57
5.4.1 Basement excavation for Midland Bank, Jersey..................... 57
5.5 Environmental remediation................................................................. 59
5.5.1 Cadmium treatment of an industrial site, New York .............. 59
5.6 Liquefaction control............................................................................ 60
5.6.1 Carrefour Shopping Center, Turkey ....................................... 60
6 CASE STUDY: SLUDGE TREATMENT PLANT, NEGERI SEMBILAN,
MALAYSIA................................................................................................... 63
6.1 Introduction......................................................................................... 63
6.2 Site conditions..................................................................................... 64
6.3 Design ................................................................................................. 66
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6.3.1 Surcharge ................................................................................ 66
6.3.2 Material specifications............................................................ 67
6.3.3 Analysis................................................................................... 67
6.3.4 Notes on FOS calculation ....................................................... 68
6.3.5 Analysis results ....................................................................... 69
6.4 Implementation ................................................................................... 69
6.4.1 Monitoring instrumentation .................................................... 71
6.5 Project review ..................................................................................... 72
7 CASE STUDY: PROPOSED COMMERCIAL BUILDING AT JALAN
PAHANG, KUALA LUMPUR, MALAYSIA ............................................ 73
7.1 Introduction......................................................................................... 73
7.2 Site conditions..................................................................................... 74
7.3 Justification for jet grouting................................................................ 76
7.4 Jet grouting design ............................................................................. 777.5 Encountered problems ........................................................................ 78
7.6 Project review ..................................................................................... 81
8 CONCLUSIONS ........................................................................................... 82
8.1 State of jet grouting............................................................................. 82
8.2 Ending notes........................................................................................ 83
9 REFERENCES.............................................................................................. 84
Appendix A................................................................................................................ 88
Appendix B ................................................................................................................ 90
Appendix C................................................................................................................ 93
Appendix D.............................................................................................................. 100
Appendix E .............................................................................................................. 134
Appendix F .............................................................................................................. 139
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LIST OF TABLES
Page
Table 1. Major chemical components of Portland cements. ...................................... 14
Table 2. Supplementary additives and admixtures in cement grouts.......................... 15
Table 3. Suitability of various chemical grouts in common applications (adapted from
USACE 1995). ................................................................................................ 20
Table 4. Historical jet grouting methods (adapted from Xanthakos et al. 1994)........ 29
Table 5. Typical range of jet grouting parameters and soilcrete formed using the
single-, double-, and triple-fluid systems (from Kauschinger and Welsh, cited
by Xanthakos et al. 1994). .............................................................................. 42
Table 6. Typical range of air, water, and grout flow parameters (estimated from Covil
and Skinner 1994). .......................................................................................... 43
Table 7. Required soil parameters for jet grouting design (adapted from JJGA n.d.).45
Table 8. Results of trial jet grouting tests in quay wall stabilization works, Kingston
Bridge, Glasgow (adapted from Coutts et al. 1994). ...................................... 52
Table 9. Operating parameters used in jet grouting basement works, Singapore Post
Center (from Ing and Teoh 2000). .................................................................. 54
Table 10. Operating parameters used in jet grouting works for the eastern tube of the
Les Hurtires tunnel........................................................................................ 57
Table 11. Operating parameters used in jet grouting basement works, Midland Bank
development (from Newman et al. 1994). ...................................................... 58
Table 12. Operating parameters used in jet grouting, Carrefour site (adapted from
Olgun 2003). ................................................................................................... 61
Table 13. Excavation depths for construction of the sludge treatment facility, Port
Dickson, Negeri Sembilan. ............................................................................. 64
Table 14. Design parameters for various soil strata.................................................... 65
Table 15. Operating parameters used in jet grouting, Negeri Sembilan site. ............. 70
Table 16. Design parameters for various soil strata.................................................... 74
Table 17. Operating parameters used in jet grouting, Jalan Pahang site. ................... 77
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LIST OF FIGURES
Page
Figure 1. Relationship of permeability to water-cement ratio (from Littlejohn 1982).
......................................................................................................................... 17
Figure 2. Relationship of bleed rate to water-cement ratio (from Littlejohn 1982). .. 17
Figure 3. Relationship of compressive strength to water-cement ratio (from Littlejohn
1982). .............................................................................................................. 18
Figure 4. Ranges of grain size in which different types of grout are useful (from
Mitchell, cited by Terzaghi et al. 1996). ........................................................ 24
Figure 5. Five stages of the jet grouting process (from Covil and Skinner 1994)...... 26
Figure 6. Generic jet grouting systems. ...................................................................... 28
Figure 7. Relationship between the projection distance from the nozzle and pressure,
for delivery pressure of 40 MPa and nozzle diameter of 2 mm (from Shibazaki
and Ohta 1982)................................................................................................ 32
Figure 8. Collision jet for soil cutting (from Shroff and Shah 1999). ....................... 36
Figure 9. Mechanical jet combined method (from Shroff and Shah 1999). ............... 37
Figure 10. Schematic view of jet grouting equipment (from Shibazaki and Ohta
1982). .............................................................................................................. 39
Figure 11. Typical track-mounted jet grouting rig (from USDOE 1998)................... 40
Figure 12. Exposed soilcrete columns. ....................................................................... 48
Figure 13. Horizontal jet grouted umbrella for tunnel structures (from Guatteri et al.
1994). .............................................................................................................. 55
Figure 14. Cross section of jet grouting works for the eastern tube of the Les
Hurtires tunnel (from Guilloux 2000). .......................................................... 56
Figure 15. Terrace housing located adjacent to the site.............................................. 65
Figure 16. Oil contaminated soil at site. ..................................................................... 66
Figure 17. Girder-mounted jet grouting rig. ............................................................... 70
Figure 18. Silo and mixing equipment........................................................................ 71
Figure 19. Site after excavation. ................................................................................. 72
Figure 20. View of entire site, Jalan Pahang project. ................................................. 75
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Figure 21. View of jet grouted slope covered with plastic sheeting........................... 76
Figure 22. Elementary school located adjacent to Jalan Pahang site.......................... 78
Figure 23. ACM complex (structure with striped roof) adjacent to the Jalan Pahang
site. .................................................................................................................. 79
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ACKNOWLEDGEMENTS
I would like to thank my supervisor, Dr. Jim Shiau, for guiding me. I would also like
to thank Mr. Lim Kean Hoe of APG Geo-systems Sdn. Bhd. for sparing the time to
talk to and help me with my case study. This project was not only taxing on me, but
on my family as well and I would like to thank them for their unfailing support
throughout this endeavor.
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1
1 BACKGROUND
1.1 Need for ground improvement
Soil, a mundane material which never crosses most peoples minds, supports many of
the structures essential to human civilization. Its importance becomes most noticeable
during its failure, when unnatural stresses imposed disrupt its equilibrium and cause
the soil particles to be rearranged in relief. Soil failures have the potential to be disas-
trous with substantial human and economic costs. One of Australias worst landslides
in recent history, the Thredbo landslide of 1997 in New South Wales, caused the
deaths of eighteen people and damage worth millions of dollars when the landslide
debris crashed into a nearby ski resort.
Guarding against soil failure is not a simple issue of avoiding weak soils. In most
countries, development tends to cluster around existing people-concentrations of cit-
ies and towns; the choice of development location is usually geographically restricted.
Furthermore, the scarcity of attractive land often causes the dual considerations of
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availability and cost to take precedence over soil suitability. As a result, problematic
soils are often unavoidable. Fortunately, geotechnical expertise provides a viable so-
lution for most situations. Various ground improvement techniques are available to
remediate unfavorable soil characteristics.
1.2 Introduct ion to grouting
Grouting is a process in which fluid grout is introduced under pressure either into the
voids of a soil mass or typically inaccessible spaces (such as buried soil strata or
foundations). The grout material displaces the existing soil, water, or air as it flows
through the void matrix, eventually curing to form a composite material with en-
hanced properties; the term soilcreterefers to a soil/grout mixture of this nature. The
primary purposes of grouting are to improve the strength and durability of the soil
and/or to control the permeability of the soil.
1.3 Development of jet grout ing
A steady stream of water can cut a canyon through rock with enough time. People
have long observed the erosive power of water and sought to harness it. The concept
of using high velocity fluid jets to erode and cement soil originated in Japan during
the mid1960s. Although chemical grouting methods were already well established in
geotechnical practice then, Shroff and Shah (1999) noted that those methods suffered
from the disadvantages of irregular grouted shapes and insufficient improved
strengths. The need for a better method spurred grouting research during that period,
and the idea of jet grouting was born. Initially inspired by the giant water jets used in
hydraulic mining, extensive research and development has since evolved jet grouting
from being a mere theoretical curiosity into an important soil improvement technique.
The first instances of jet grouting emerged during the early1970s. Two methods
were developed independently at the outset: the chemical churning pile (CCP)
method and the column jet grout (CJG) method. The CCP method was a single-fluid
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system in which chemical grouts were injected under pressure through a small nozzle
located at the end of the drill rod. The CJG method was a triple-fluid system in which
the soil was first cut with an air-coated-water jet before being mixed with a cement
grout jet. In both methods, the simultaneous actions of lifting and rotating would re-
sult in the creation of a soilcrete column.
Jet grouting quickly gained acceptance in Japan during the 1970s and spread around
the world in the following decades. Initial activity was concentrated around Germany,
Italy, France, Singapore, and Brazil (Xanthakos et al. 1994). Widespread adoption in
the United States did not occur until after 1987 (Schaefer 1997). Today, the technique
is practiced in many countries where specialist grouting contractors are available.
1.4 Areas of application
A grouting program can be designed to achieve a variety of results depending on the
method and grout type used. In general, ground treatment applications can be divided
into several groups, differentiated by objective. The primary areas of application are
mechanical property improvement, permeability and erosion control, and settlement
control. Numerous other applications exist, of which some are also described in this
section. It should be noted that the following examples are meant to be illustrativeonly and offer but a partial representation of all the different ways grouting is used in
practice.
1.4.1 Mechanical property improvement
In mechanical property improvement applications, grouting is used to improve the
bearing capacity and other structural properties of a soil or rock mass. Grouted soils
typically exhibit higher strength capacities than normal soils. The grout in the void
matrix binds the soil particles together in a manner similar to how cement paste binds
aggregates together in concrete. The shear resistance of the soil is increased due to the
binding effect of the grout. The enhanced stiffness also reduces any deformations and
settlements which might arise in response to stresses.
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Another use of grouting is for the consolidation of loose soils. For example, it is de-
sirable in tunnel construction to bore through a stable body of rock which will not
collapse into the shaft. If fragmented rocks or loose soils are encountered, grouting
can be used to consolidate the ground during the shaft-driving process (with the side
benefit of improving tunnel face stability).
1.4.2 Permeability and erosion control
In permeability control applications, grouting is used to control the effects of
groundwater. The primary areas of application include dam-, tunnel-, and foundation
construction, where deep excavations make groundwater a major construction issue.
It is intuitively obvious that grouted soils should have a lower permeability than ordi-
nary soils, as the grout material fills up the void space through which water normally
travels.
In deep excavations, grouting can be used to facilitate construction works and pro-
mote stability in excavated faces. By grouting walls and base rafts bounding the site,
the permeability of the excavated faces can be drastically reduced to decrease the
amount of groundwater flow into the site. Combined with proper pumping and drain-
age, the site can then be prepared for access by construction personnel and equipment.
In dam construction, grouting is used to reduce the seepage under a dam, either by
eliminating flow entirely or by reducing it to a point where the remainder can eco-
nomically be drained. A grout curtain, essentially a panel of grouted soil acting as an
impermeable wall, can be constructed underneath the dam to form a cutoff wall. Al-
though grouting is not the only way of constructing this barrier, the method is a viable
option which should be considered seriously. One additional benefit of reducing
groundwater flows isillustrating yet another area of applicationthat internal ero-
sion within the foundation and embankments is reduced.
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1.4.3 Settlement contro l
Grouting can also be used as a measure to correct excessive ground settlements and
deflections. Grout is injected into a buried stratum where settlement is to be corrected.
The grout builds up in bulk until it eventually forces the overlying soil burden up-
wards. This is sometimes used to minimize settlement effects when boring tunnels
underneath existing structures. Another example is in pavement construction where
grout may be pumped underneath pavement slabs to lift them (i.e., slab-jacking).
1.4.4 Other applications
Many other specialized applications of grouting exist in addition to those described
above. In environmental applications, grouting is used to control contaminant migra-
tion through the ground and to treat contaminated soils. These are typically extended
cases of permeability control, in which grout is used to reduce contaminant transport
through groundwater flows. Chemical grouts are usually used, mixed thoroughly into
the contaminated soil so that the neutralizing chemicals come into full contact with
the contaminants. In loose saturated sands, grouting may be used to mitigate the like-
lihood of liquefaction (a rapid loss of strength when subject to dynamic motions).
1.5 Grouting methods overview
There are many ways in which the simple action of introducing grout into soil can be
performed; this is reflected in the diversity of existing grouting methods. The broad
range of available options means that acceptable grouting solutions can be found for
nearly any ground improvement problem. Many methods have long histories of suc-
cessful application behind them and are routinely prescribed with confidence. Others
are constantly being developed and refined with the introduction of new materials and
construction techniques.
While no definitive classification system for all grouting methods exists, there are
several ways of organizing them into groups. Specific grouting methods are discussed
under the headings of these groups. It should be noted that the distinction between
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some of these specific methods is blurred at times and a particular implementation
may be correctly classified under several titles at the same time. Nevertheless, it is
expected that the following discussion will provide an explanation of most common
grouting method terms referred to in practice.
1.5.1 Grouting methods by grout type
The simplest basis of identifying grouting methods is to note the type of grout being
used. The most common examples under this organization are chemical grouting and
cement grouting (since these are the principal grouts used in practice). As the names
imply, chemical grouting involves the use of a chemical grout while cement grouting
involves the use of a cement grout. Besides these, other references to methods using
specialized grouts exist (e.g., foam grouting, referring to the use of expansive foam
grouts). These terms do not provide extra information about the actual grouting proc-
ess being used.
1.5.2 Grouting methods by process
Grouting methods can also be grouped with a construction-process-oriented focus.
Examples include stage grouting, circuit grouting, tremie grouting, etc.
Stage grouting
In stage grouting, drilling and grouting occurs in progressive stages. In ascending-
stage grouting (or upstage grouting), drilling is first completed for all of the stages to
be treated. The hole is then flushed of cuttings, and the stage is sealed with a me-
chanical device called a packer. Grout is then pumped into the isolated stage and al-
lowed to cure before the next stage located immediately above is grouted.
In descending stage grouting (or downstage grouting), the grouting process reverses
in direction; the grouting proceeds sequentially from the upper stages to the lower
stages. After each stage is grouted, the borehole is extended to the depth of the next
stage and the process is repeated. Packers are used where necessary.
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Circuit grouting
Circuit grouting involves the use of a dual line system in which grout is circulated
continuously. The pumped grout fills the hole and flows back up in an external vented
casing. At the top, grout which has not entered the ground is collected back and re-
circulated into the system. In practice, circulation grouting is rarely used now (Bruce
2002).
Tremie (or gravity) grouting
In tremie (or gravity) grouting, the grout flows into the borehole under the influence
of gravity. A hole is first drilled and a tremie pipe is lowered to the bottom. Grout is
subsequently pumped in at gravity pressure (i.e., under the pull of its own weight). As
the gaps are filled, pressure will start to build up in the pipe and the pipe is raised.
Various casing methods
It is common to employ some form of casing or sheathing when grouting in weak
soils so that the borehole walls will not collapse. A casing of some form may be
drilled, pushed, or otherwise placed to the full treatment depth before progressively
being withdrawn as grouting proceeds.
One common casing method is the tube--manchettesystem, which employs a perfo-
rated grout pipe with rings of small holes spaced at specified intervals. A rubber
sleeve fits tightly around each ring of holes to act as a one-way valve, allowing grout
to flow out of the pipe but not back in.
1.5.3 Grouting methods by mode of interaction
Another way to distinguish between grouting methods is to identify the manner in
which the grout interacts with the soil structure to achieve a function. Four methods
are briefly described below: permeation grouting, compaction grouting, hydrofracture
grouting and jet grouting. For each method, minor variations (in sequence, arrange-
ment, etc.) may exist.
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Permeation grouting
In permeation grouting, a hole is drilled into the ground to the depth of the treatment
strata and an injection pipe is inserted. Liquid grout is then pressure-injected steadily
into the void space of the soil volume with minimal disturbance to the original soil
structure. As the grout solidifies, the soil particles are bound together to form a hard-
ened mass (akin to how cement paste binds aggregates together in concrete). The re-
sultant composite material possesses higher shear and compressive strengths than the
ungrouted soil. The increased resistance to deformations also improves the bearing
capacity and erosion resistance of the soil.
Permeation grouting also has the effect of reducing soil permeability. As the grout
advances through the soil matrix, water and gases are expelled from the pores. The
grout-filled pores considerably reduce permeability and water flow within the soil
mass. This ability to significantly modify soil permeability characteristics makes the
method useful in groundwater control applications (e.g., basement construction).
Compaction grouting
In compaction grouting, a thick grout is pumped into the soil as a contiguous mass to
displace existing soil to the sides. Due to its high viscosity, the grout expands out-
wards to form a homogeneous bulb rather than permeating into the soil voids. Duringthis expansion process, the adjacent soil is progressively displaced to the sides and
compacted, resulting in increased shear resistance.
Compaction grouting is most effective in loose granular soils. The primary purpose of
compaction grouting is to increase the bearing capacity of a soil mass in supporting
vertical foundation loads. The soil densification also reduces settlements and the like-
lihood of liquefaction by decreasing the void ratio and increasing frictional contact
between grains.
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Hydrofracture grouting
In hydrofracture grouting, grout is pumped into the soil at pressures which exceed the
tensile strength of the soil. This causes local failures to materialize as fissures and
cracks within the soil. The grout subsequently flows into these crevices to form grout
lenses. Hydrofracture grouting is a form of compaction grouting because the grout
lenses compact the soil. The method is used in low permeability soil types ranging
from weak rocks to clays.
Jet grouting
In jet grouting, a pressurized fluid jet hydraulically cuts into the soil before grout is
mixed into the ensuing soil slurry. The cutting jet is typically located at the tip of a
modified drill bit. As the bit rotates, soil is eroded in a radial pattern at the level of the
jet. The drill is then lifted from the bottom of the borehole and grout is injected in a
similar fashion to the cutting fluid. An approximately circular column of grouted soil
is created by this process. More details on this method are provided throughout this
paper.
1.5.4 Other grout ing methods
Two grouting methods which do not readily fit into other categories are listed under
this section.
Compensation grouting
Compensation grouting, a form of compaction grouting, is a controlled displacement
method used primarily in tunneling applications. Grout is injected in precise quanti-
ties between the tunnel excavation and the foundations of surface structures so as to
reduce or offset any settlements which may occur. As the description implies, the
process needs to occur concurrently with tunnel driving. Intensive monitoring of real-
time ground and surface structure movements is required so that grouting parameters
can be continuously adjusted to keep soil deformations within prescribed limits.
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Curtain grouting
Curtain grouting refers to the creation of a subsurface grout wall which reduces or
stops seepage. A common area where grout curtains are used is for the construction of
cutoff walls underneath dams. A series of closely-spaced holes parallel to the dam
alignment (or normal to groundwater flow) are drilled and grouted. The resultant
grouted zone forms a low-permeability barrier which arrests groundwater flows.
Grout curtain configurations may differ depending on the needs of a specific applica-
tion. It should be noted that grout curtains may be inclined (controlled by the drilling
angle) or vary dimensionally along its length. For concrete dams on sound rock, the
installation of a single grout curtain typically suffices. On weaker rocks, the installa-
tion of multiple grout curtains may be required.
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2 GROUTS
2.1 Grout classification
Grout materials are broadly divided into particulate and solution types. Particulate
grouts, also known as suspension- or coarse-grouts, consist of particulate solids sus-
pended in a fluid medium. Examples include cement, cement-bentonite, and soil-
water grouts. Solution grouts are chemically based grouts containing a homogenous
mixture of two or more substances. Examples include silicates, acrylics, urethanes,
and resins. Many chemical grouts are toxic by nature and are unused due to handling
difficulties or environmental regulations.
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The distinction between cement and chemical grouts is increasingly being blurred as
new grout types are introduced. Microfine cements exist with suspended-particle di-
ameters less than 10 m. Chemical grouts with particle diameters of 10 to 15 nm have
also been developed (USACE 1995).
2.2 Grout properties
Various chemical, mechanical, and rheological properties of a grout must be exam-
ined in order to evaluate its suitability for a particular soil and/or application. Some of
the properties by which grouts are assessed are listed below.
Viscosity
Viscosity is the property of a grout to resist deformation when subject to shear
stresses. It is commonly embodied in the concept of thickness; a syrupy fluid has high
viscosity while a runny fluid has low viscosity. Viscosity is one of the main factors
affecting the ability of a grout to flow through a soil.
Thixotropy
Thixotropy is the property of a grout to exhibit a decrease in viscosity when subject to
prolonged shear stresses. In other words, a thixotropic grout may normally be of a
thick consistency, but will turn fluid when subject to agitation.
Gel/set time
Gel time refers to the time between the initial mixing of the components of a chemi-
cal grout and the formation of a viscous gel. Gel time determines when a grout thick-
ens and loses its ability to flow. A good grout should have a gel time which lies
within a narrow range. The gel time should be long enough for the grout to penetrate
the soil, but short enough such that it will not be washed away by groundwater flows.
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Suspended particle size
The size of suspended particles in a grout affects its ability to penetrate into a particu-
lar soil. In general, cement grouts are effective in coarse-grain-sized soils while
chemical grouts are effective in fine-grain-sized soils.
Strength
The unconfined compressive strength of grout-treated soil samples should be tested in
order to estimate the strength of the eventual grouted soil. Both dry and saturated
samples should be tested.
Durability
Durability refers to the ability of the grout to withstand hostile environmental condi-
tions such as repeated drying and wetting or freeze-thaw cycles.
Cohesion
Cohesion refers to the ability of the grout to maintain integrity. In cohesive particulate
grouts, the suspended particles remain in suspension when at rest. Minimal segrega-
tion and bleeding (the development of free water at the surface of a grout at rest) oc-
curs.
Stability/sensitivity
Certain chemical grouts may become unstable under environmental conditions such
as extreme temperature changes, presence of other substances in groundwater, etc.
Such irregular conditions are to be identified and grouts sensitive to these conditions
should be avoided.
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2.3 Cement grouts
The most common particulate grouts are mixes using ordinary Portland cement, due
to the familiarity, economy, and widespread availability of the material. In contrast to
concrete mixes, cement grout mixes typically do not contain aggregate materials.
Fluid or hardened mixtures of cement and water are sometimes referred to as neat
cements.
2.3.1 Review of Portland cements
Portland cements are hydraulic cements which harden via reaction with water (i.e.,
hydration). These cements contain varying proportions of five principal chemical
compounds, which are listed in Table 1. When the cement compounds come into con-
tact with water, they react to form a calcium-silicate-hydrate gel (3CaO2SiO23H2O,
commonly abbreviated C-S-H) with binding properties.
Table 1. Major chemical components of Portland cements.
Compound Chemical formula Abbreviation Notes
Tricalcium silicate 3CaOSiO2 C3SHardens rapidly;
contributes to initial setand early strength.
Dicalcium silicate 2CaOSiO2 C2SHardens slowly;
contributes to strengthgains beyond first week.
Tricalcium aluminate 3CaOAl2O3 C3A
Generates high heats ofhydration; low C3A
contents give sulfateresistance
Tetracalciumaluminoferrite
4CaOAl2O3 Fe2O3 C4AFAssists manufacturing
process; contributeslittle to strength
Calcium sulfatedihydrate(Gypsum)
CaSO42H2O -Slows C3A reaction rate;
controls set time
Major categories of Portland cement include ordinary cement, high-early-strength
cement, low-heat-of-hydration cement, and sulfate-resistant cement. The distinguish-
ing properties of these cements derive from varying the proportions of the major
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chemical components. Detailed information on the specific mix proportions can be
obtained from cement suppliers or cement-standards references.
2.3.2 Supplementary addit ives and admixtures
Besides the primary cement compounds, additional chemicals and materials may be
added to a grout mix to modify its fluid and set properties (i.e., strength, penetrability,
and other grout characteristics). A list of supplementary materials which may be
added to a grout mix is shown in Table 2. A well designed grout mix creates a stable
suspension with high penetrability. By optimizing grout performance and effective-
ness, economy can be realized through smoother grouting operations.
Table 2. Supplementary additives and admixtures in cement grouts.
Material Function (s) Notes
Pozzolans(fly ash, silica fume,natural pozzolans,
etc.)
React with calcium hydroxide(Ca(OH)2), a byproduct of hydration,
to form additionalcementitious products.
Fly ash, the most common pozzolan,is a byproduct of burning coal.
BentoniteImprove stability;
improve workability;reduce shrinkage and bleeding
Bentonite is a natural clay composedlargely of a mineral called
montmorillonite. It can absorb a lot ofwater and will expand significantly.
Retarders Delay setting time.May be used under
hot weather conditions.
Accelerators Accelerate setting time.May be used under
cold weather conditions.
Water reducers,superplasticizers
Increase workability;reduce water content;improve strength; and
reduce porosity and permeability.
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Shrinkage-reducingagents / expanders
Moderate or eliminateshrinkage effects.
Shrinkage is not normally a problemin wet underground conditions.
Anti-washout agentsIncreases grout viscosity to
reduce grout permeability andpossible dilution by groundwater
May be used in high-soil-permeabilityor high-groundwater-flow conditions.
Air-entraining andair-detraining
agentsAdjust air content of cement. Rarely used.
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2.3.3 Filler materials
Fine sands are sometimes added as filler material to neat cement for reasons of econ-
omy. As in concrete, the presence of aggregates improves strength (by lowering wa-
ter-cement ratio requirements), durability, and shrinkage performance. In general,
uniformly graded sand with high sphericity (i.e., rounded as opposed to angular or flat)
is preferable as pumpability increases. Littlejohn (1982) recommends a range of 5
mm75 m diameter particles, but suggests that the maximum diameter be reduced to
0.5 mm for long pumping distances of over 300 m to avoid segregation.
Studies by the U.S. Army Engineer Waterways Experiment Station (USACE 1984)
have indicated that a mixture of two parts sand to one part cement can be pumped
without the aid of admixtures at normal temperatures. Small amounts of clays may
also be added to improve the sand-carrying capacity, in addition to providing minor
benefits such as reduced bleeding and improved workability.
2.3.4 Water-cement ratio
One of the most important parameters of a grout mix is the water-cement ratio. A low
water-cement ratio will have wide-reaching effects such as reducing bleeding, reduc-
ing workability (related to viscosity and pumpability), improving strength and dura-
bility, etc. Water-cement ratios today typically have a maximum value of two to three(Bruce 2002). Where strength is a prime criterion, a water-cement ratio of around
0.51.0 may be used.
Critical design properties such as bleeding, fluidity, strength, and permeability of neat
cement mixes can be correlated with the water-cement ratio. Littlejohn (1982) pre-
sents a concise discussion of the major design parameters of cement mixes and some
of the theoretical relations behind them (interested readers are referred to his paper
for more detailed information). Some of the effects of the water-cement ratio on ce-
ment are shown in Figures 1 to 3. The permeability of a grout increases at a roughly
exponential rate with the water-cement ratio, increasing gently until a ratio of around
0.5 before it suddenly rockets. The bleed capacity of a grout also increases with the
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water-cement ratio; this is logical as high water contents would suggest more poten-
tial for bleeding. The compressive strength of grouts also tends to increase with lower
water-cement ratios.
Figure 1. Relationship of permeability to water-cement ratio (from Littlejohn 1982).
Figure 2. Relationship of bleed rate to water-cement ratio (from Littlejohn 1982).
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Figure 3. Relationship of compressive strength to water-cement ratio (from Littlejohn 1982).
2.4 Chemical grouts
Chemical grouts are chemically reactive solutions which solidify into a gel after a pe-
riod of time. While chemical grouts may contain solid and liquid phases as particulate
grouts do, it is assumed that any solid phase will be on such a small scale that overall
behavior will essentially be that of a liquid. Chemical grouts typically exhibit very
low viscosities, which enable them to flow through finer-grained soils with pore sizes
that cannot accommodate conventional particulate grouts.
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2.4.1 Chemical grout systems
A complete chemical grout system comprises of several typically-aqueous constitu-
ents, including a base, a reactant/catalyst, possibly accelerators/activators or inhibitors,
and other optional additives. The base material is the chemical(s) which reacts to
form the gel. The reactant initiates reaction with the base material. Accelerators and
inhibitors may be added to alter the rate of reaction, speeding or slowing it down re-
spectively. Depending on the compounds used, the mix will set and harden at a prede-
termined rate matched to the requirements of a particular application.
Chemical grout systems may be one-step or two-step processes. In one-step processes,
all ingredients of the system are mixed before being injected, relying on the delay in
gel time to achieve sufficient permeation into the soil. Gel time control is obviously
critical in such processes. In two-step processes, the ingredients are injected sepa-
rately and mixed in-situ. The components will react to form a gel mass after a set pe-
riod of time.
2.4.2 Chemical grout classification
Chemical grouts may be divided into the following categories (adapted from USACE
1995):
1. Sodium silicates
2. Acrylates (and acrylamides)
3. Lignosulfonates
4. Polyurethanes
5. Others
As many chemical grout formulations are highly toxic in nature, environmental and
safety considerations limit field usage to only select types. Of the grouts listed above,
sodium silicates and certain acrylics are the most common by far. It is estimated that
in the United States alone, these two materials have a combined market share of
around 85% to 90% (Karol 2003).
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2.4.3 Chemical grout usage
The suitability of different chemical grout types for use in common applications is
shown in Table 3.
Table 3. Suitability of various chemical grouts in common applications (adapted from USACE1995).
Type
Appl ication
Sodiums
ilicates
Acrylates
Lignosulfonates
Polyurethanes
Adding strength C1
C C R
Reducing water flow C C C U
Load transfer and support U U U C
Anchor installation R R R U
1C = commonly used; U = used; R = rarely used
2.4.4 Sodium sil icates
Sodium silicate (SiO2Na2O) is an alkali silicate which is soluble in water (hence its
generic name water glass). Commercial formulations typically come in aqueous form.
Sodium silicates are the most popular chemical grouts in practice because their negli-gible toxicity lends to safety and environmental compatibility.
Sodium silicate systems operate on the basis of precipitating the silicate component
via the pH-neutralization of the solution. The system remains aqueous because the
alkaline sodium oxide (Na2O) maintains the pH at a level where the weakly acidic
silica (SiO2) can be dissolved (PQ Co. 2005). Lowering or neutralizing the pH re-
duces the solubility of the silica so that it precipitates and polymerizes (i.e., combine
repeated units of smaller molecules to create a larger one) to form a gel. The silica-to-
alkali ratio is particularly important because ratios of three to four will yield gels with
adhesive properties suitable for grouting (Karol 2003).
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Properties of the grout and grouted soil can be adjusted by varying the different pro-
portions of grout constituents. The gel time of the grout is controlled by the amount of
reactant or catalyst material present. Higher concentrations (with respect to the base)
will speed up the rate of gel formation; this has important implications in gel-time
control for singe-step processes. The viscosity (which affects the penetrability) of the
grout is directly proportional to the sodium silica concentration; i.e., more sodium
silicate in water will produce a thicker solution. Grouted soil strength also varies di-
rectly with the silica content, with higher concentrations producing stronger results.
Problems with silica gels
There are two main problems associated with silica gels which may raise questions
about the performance and durability of sodium-silicate-grouted soils. The first is a
phenomenon known as syneresis, referring to a tendency of fresh silica gels to expel
water and shrink. The severity of syneresis is dependent on silica content and setting
time, and the phenomenon generally diminishes with age (Karol 2003). Syneresis
causes a slight increase in grouted-soil permeability which may be an issue in perme-
ability-control applications.
Another problem is the loss of strength in grouted soils under water, which may vary
from negligible to complete dependent upon the grout chemistry (Karol 2003). Thesilica gel undergoes a dissolution reaction which reverses gel formation and dissolves
the bonds holding the soil together. The severity of the dissolution increases with the
amount of unreacted soda, with low-reactant-concentration and long-set-time mix-
tures being particularly aggravating (Karol 2003).
2.4.5 Acrylamides and acrylates
Acrylamides were developed in the 1950s as a successful grout with high penetrabil-
ity, good strengths, and good gel-control times. Viscosity also displays a near-ideal
pattern of remaining constant from initial mixing till a sudden rapid increase at set
time. Acrylamide grouts consist of a base mixture containing acrylamide monomers
(which polymerize to form long molecular chains) and a cross-linking agent (which
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binds the acrylamide chains together). The stiffness of the grout is varied by altering
the ratio of the acrylamide to the cross-linking agent; lower acrylamide proportions
will yield stiffer gels with higher strengths (Karol 2003). Gel formation is initiated by
the addition of a reactant and optional additives.
Despite the excellent grout characteristics of acrylamide, usage has been tempered by
its neurotoxic properties (i.e., it damages the nervous system). In grouting operations,
the risk of acrylamide poisoning can be minimized to negligible levels with basic
handling and safety precautions. As the grout enters a gel form, the free-acrylamide
concentration becomes diluted to such a degree that it may be considered non-
hazardous. (Karol 2003)
Acrylates were introduced in the early1980s in response to the need for a less toxic
alternative to acrylamides. Acrylates behave similarly as acrylamides, although they
possess higher viscosity, lower strength, and poorer gel-time control (Karol 2003).
The most important difference is that acrylates have much lower toxicities are not
neurotoxic.
2.4.6 Lignosulfonates
Lignosulfonates are produced as waste byproducts of the paper (and other wood-
processing) industry. The chemistry of lignosulfonates is complex as the specific con-
tent of a mix will vary depending on tree source, paper mill, etc. However, there is
common agreement between most experts that lignosulfonates contain benzene-type
molecules of some type (Karol 2003). A chromium compound (typically sodium di-
chromate Na2Cr2O72H2O) is used to oxidize the lignosulfonate so that an insoluble
gel is formed.
The hexavalent chromium and the benzene components in lignosulfonates grouts are
highly toxic. Due to the potential dangers of these chemicals being leached into the
environment, lignosulfonate grouts are generally not recommended for use in ground
improvement.
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2.4.7 Polyurethanes
Polyurethane is a rubbery foam material created by the reaction between certain
chemicals. Different forms exist, but all depend on reacting isocyanates (a chemical
group of nitrogen, carbon, and oxygen atoms) with hydroxyl-containing compounds
(hydroxyl is the oxygen-hydrogen anion OH) to form a polymer with a cross-linked
structure. In grouting applications, the use of prepolymers (an intermediate form be-
tween a monomer and a polymer) with partially-reacted isocyanates is useful (Karol
2003). Other additives may be also included in a mix for various purposes; for in-
stance, a blowing agent may be incorporated to modify foam-bubble sizes.
Polyurethane grouts are generally divided into one-component and two-component
systems. One-component systems (also known as water-reactive polyurethanes) use
prepolymers which are reacted with water to complete the polymerization process and
produce polyurethane foam (USACE 1995). Two-component systems use other hy-
droxyl-containing compounds to produce polyurethane foam.
Cured polyurethane foam is an inert material generally considered nontoxic. The pri-
mary risk lies within the isocyanate component, which may have varying levels of
toxicity depending on its exact chemical formulation (USACE 1995). Some polyure-
thane materials may pose a flammability hazard.
2.5 Groutability
In many types of grouting where a chemical or cement grout is to be injected into the
ground, the groutabilityof the soil must be considered. The concept of groutability
refers to how well a soil is able to accept grout. It is a function of the relative size of
the soil pore space to the maximum size of suspended particles in the grout. The US
Army Corps of Engineers (1984) expresses groutability as a ratio of percentage-
passing sieve sizes of a cement, sand, or gravel. As an approximate guide, the grain
sizes for which various grouts are applicable are shown in Figure 4.
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Groutability is not as significant an issue in jet grouting as compared to other methods
because jet grouting destroys the soil structure as part of the process. Any soil which
can be eroded can potentially be jet grouted.
Figure 4. Ranges of grain size in which different types of grout are useful (from Mitchell, cited
by Terzaghi et al. 1996).
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3 JET GROUTING BACKGROUND
3.1 Introduction
Jet grouting is a technique characterized by the use of a pressurized fluid jet to hy-
draulically erode soil either before or concurrent with the addition of grout materials.
Considerable flexibility in the final grouted configuration can be achieved through
varying different parameters such as insertion angle, rotation and lifting rates, layout
and arrangement, etc. The most common grouted shape is the columnar element pro-
duced by controlled lift and rotation. If rotation is omitted, a panel element may be
produced. More complex shapes such as curtain walls, foundation rafts, and gravity
mass walls may be formed through an interlocking combination of the aforemen-
tioned basic elements. These elements constitute the building blocks of the geotechni-
cal engineer, to be arranged and combined imaginatively into a coherent geotechnical
solution.
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Figure 5 below gives a visual overview of the triple-fluid jet grouting process, divided
into five steps labeled ae. (a) A borehole is first drilled into the ground to the base
depth of the treatment strata. Typically a rotary drill of some type is used for this pur-
pose. (b) Jetting is then initiated with the air-coated water jet cutting into the soil. The
jet destroys the soil structure and creates a slurry which is then flushed out as grout-
ing progresses. (c) As the rod is lifted and rotated at controlled rates, a grout jet fills
the columnar void and replaces the soil slurry. (d) Once the target column height is
achieved, the rod is extracted and grouting begins anew at a new location. (e) Grout-
ing in immediately-adjacent areas usually does not begin until the grout column has
had some time to cure. Different column elements can be merged into a single struc-
ture by grouting the spaces in between.
Figure 5. Five stages of the jet grouting process (from Covil and Skinner 1994).
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3.2 Jet grout ing variants
A number of different jet grouting variants have been developed since the seventies.
The original chemical-churning-pile and column-jet-grout methods are still in use to-day in evolved forms.
3.2.1 Generic systems
Modern jet grouting methods are broadly divided into three generic classes: single-,
double-, and triple-fluid systems (see Figure 6).
Single-fluid system
In single-fluid systems, grout is jetted directly to cut and mix with the soil. Of the
three systems, this is the simplest method. Mixing action dominates as only part of
the soil is removed effectively. Single-fluid systems produce the smallest-diameter
columns, but the columns are also the strongest for the same amount of cement used.
Double-fluid system
Double-fluid systems are a refinement of single-fluid systems in that a conical shroud
of compressed air is added around the grout jet. The air shroud enhances the cutting
ability of the grout jet by reducing the amount of energy losses; friction is reduced asthe grout is isolated from the surrounding soil environment. Double-fluid systems
produce larger-diameter columns than single-fluid systems (roughly double in diame-
ter). However, the columns produced by this system are also the weakest due to the
high amounts of air entrained into the cement.
Triple-fluid system
In triple-fluid jet grouting, the job of soil erosion is shifted to an additional water jet
located above the grout jet. Similar to the double-fluid system, a compressed air
shroud is applied to the water jet to minimize energy losses. In a typical setup, an air-
shrouded-water jet will first cut into the soil to form a cavity while grout is jetted in
through a lower nozzle to replace the fluidized soil mass. This system produces the
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largest column diameters (since the air-water jet cuts soil more effectively than the
air-grout jet) which are roughly triple those of the single-fluid system.
Figure 6. Generic jet grouting systems.
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3.2.2 Note on historical systems
Table 4 summarizes a few jet grouting methods which have been historically notable.
The methods originated in Japan throughout the seventies and eighties. The research
and development work for these methods was primarily performed by two groups,one headed by Nakanishi and the other headed by Yahiro (Xanthakos et al. 1994).
Table 4. Historical jet grouting methods (adapted from Xanthakos et al. 1994).
OriginalJapanese
name
Principle ofoperation
Jettingpressure
Nozzlediameter
Rotationrate
Anticipatedcolumn
diameter
(MPa) (mm) (rpm) (cm)
Chemicalchurning pile
(CCP)Single grout jet 2040 1.23.0 20 3060
Jumbospecial grout
(JSG)
Single air-coatedgrout jet
20 3.03.2 6 80200
Columnjet grout
(CJG)
Upper air-coatedwater jet andlower grout jet
4050
1.83.0(upper)
3.05.0(lower)
5 150300
Super soilstabilization
management(SSS-Man)
Air-coatedwater jet used toexcavate; grout
tremied in
2060 2.02.8 37 200400
It can be seen that the CCP, JSG, and CJG methods are the precursors of the modern
single-, double-, and triple-fluid systems respectively. The last method, SSS-Man, is
different from the others in that after the air-water jet is used to erode a cavity, a sonic
transducer is used to survey the hole and further jetting is conducted if required (Xan-
thakos et al. 1994). Grout is backfilled in subsequently. While expensive and slow,
the procedure does ensure that column dimension specifications are met strictly and
that there is a high degree of soil replacement.
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3.2.3 Subvertical jet grout ing
Subvertical jet grouting refers to the grouting operations in which the drill rod is ori-
ented at angles up to a horizontal alignment (i.e., non-vertical). Any of the methods
described previously may be used. It is a feature of jet grouting that inclined colum-
nar elements can be constructed easily; this becomes useful in urban applications
where grouting works may have to be carried out in congested underground areas, or
in tunneling works where a supporting roof structure may be required. It is noted that
for near-horizontal alignment applications, nearly all jet grouting is carried out using
the single-fluid system as the benefits of using air shrouds become reduced. Schaefer
et al. (1997) recommends that air should not be used in jet grouting works where the
rod angle is inclined beyond 30 from vertical, as it tends to fracture the ground and
cause heave.
3.2.4 Multiple-stem grout ing
In multiple-stem grouting, two or more parallel jet grout rods are used in close prox-
imity. The idea is to improve the control of grouted dimensions and consistency by
overlapping the influence zones of adjacent rods. As the jets from adjacent rods come
into contact with each other, their fluid energies are dispersed to create a turbulent
zone of high mixing. Examples of twin-stem systems are given in Andromalos and
Gazaway (1989), which describes the construction of retaining wall of a pier in Vir-
ginia, and in Schaefer et al. (1997), which describes the grouting of a permeability
barrier for Philadelphia International Airport.
3.3 Jet grout ing notes
An array of diverse issues concerning the physical mechanisms behind jet grouting is
presented in this section. The discussion is intended to promote the understanding of
jet grouting processes through collating the experience and knowledge published by
grouting contractors and researchers.
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3.3.1 Eroding mechanism
Soil is cut by the kinetic energy of the high-pressure fluid jet. While the mechanism
of destruction is not completely clear, the following actions are believed to be in-
volved, either singly or in combination (JJGA n.d.):
1. Dynamic pressure
2. Intermittent load of jet water
3. Water wedge effect
4. Impact force of water
5. Cavitation
As the impact from the water jet breaks up the soil particles, a vacuum effect is cre-ated around the jet. Adjacent particles are pulled into the area and accelerated to high
speeds.
3.3.2 Replacement versus mixing action
In the formation of grouted elements, only two types of action take place: replace-
ment or mixing. Replacement refers to the displacement of existing soil by grout; per-
fect replacement would suggest that soil is completely replaced by the cement grout.
By contrast, mixing refers to the grout being mixed into the soil; there are no sugges-
tions being made as to the exact proportions or the degree of homogeneity.
For practical purposes, a combination of both generally occurs. The different jet
grouting methods are characterized by different relative proportions. For single-fluid
systems, the jetted soil tends to be stiffer and more mixing than replacement occurs.
In triple-fluid systems, the jetted soil is fluidized by the air and water jets so that the
grout is more easily able to displace the slurry mass, leading to higher degrees of re-
placement.
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3.3.3 Air shroud
As jet grouting typically occurs underground below the water table, significant energy
dissipation occurs as a water jet is ejected into submerged soils. Shibazaki and Ohta
(1982) have shown that the addition of a conical shroud of compressed air improves
the cutting efficiency of a water jet; the projection distance is increased slightly to a
value between that of the jet in water and that of the jet in air (see Figure 7). It is ob-
served that a water jet may have an effective distance of more than 2 meters in air,
while this distance becomes extremely diminished when the jet is under water. Sur-
rounding the water jet with air enables the effective distance to increase nearly five-
fold under submerged conditions.
Figure 7. Relationship between the projection distance from the nozzle and pressure, for deliverypressure of 40 MPa and nozzle diameter of 2 mm (from Shibazaki and Ohta 1982).
Shroff and Shah (1999) undertook a theoretical study of a two-phase model of a water
jet sandwiched between two air jets to attempt to understand the phenomenon. It was
confirmed that the shear force at the outer boundaries is reduced for a two-phase fluid
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(as compared to a single-phase fluid), thus enabling the air-coated water jet to travel
further.
3.3.4 Airli fting effect
The use of a jetted air shroud creates tiny air bubbles in the eroded soil slurry which
imparts a buoyant lifting effect that aids the removal of spoils from the borehole. As
rod angles become inclined and approach horizontal alignments, this lifting effect be-
comes diminished. This is the main reason why single-fluid systems (which do not
contain an air stream) are used almost exclusively in horizontal jet grouting.
3.3.5 Volume versus pressure
A 1982 study by Brazilian specialist contractor firm Novatecna showed that the most
important parameter influencing the size of jet grouted columns is the jet momentum
(Covil and Skinner 1994). As momentum is defined as the product of mass and veloc-
ity, two apparent approaches to boosting jet momentum are immediately suggested.
The first is to concentrate on the velocity component by increasing jetting pressures.
The second is to concentrate on the mass component by increasing the volume flow
rate. Shroff and Shah (1999) argue that while both approaches have been shown to
improve cutting ability, the latter approach of increasing the flow rate is safer as the
dangers of working with extreme pressures are avoided. Covil and Skinner (1994)also note that while a high-volume approach may be more efficient in terms of energy,
it does have drawbacks such as more wastage and the need to dispose of a corre-
spondingly higher volume of spoils.
3.3.6 Spoils return
The return of eroded cuttings is an important consideration in jet grouting works. The
borehole is typically drilled slightly wider (typically around 150 mm diameter) than
the drill rod such that an annulus through which excess spoils can escape is formed.
During jetting operations, a steady flow of return spoils is maintained to ensure that
excessive pressure does not build up to cause undesirable fracturing and heave in the
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ground. Various measures such as pre-drilling, cased-hole drilling, etc. may be used
to aid this function.
3.4 Strengths and limi tations
The jet grouting method possesses a number of unique properties which differentiates
it from other geotechnical solutions. Some of the strengths and limitations of the
method are presented below.
3.4.1 Improvement of physical properties
Jet grouting can be carried out to modify various properties of a soil mass, including
strength, permeability, density, liquefaction resistance, etc. Besides the inherent mate-
rial property differences in the composite soilcrete material, several other factors im-
part positive effects to adjacent soil mass. The impact of high pressure jets compacts
adjacent soils within a zone of certain radii. In addition, the erosive process creates a
highly irregular soilcrete surface with good side-frictional resistance.
It should also be noted that a soilcrete element will provide several of the aforemen-
tioned improvements simultaneously (e.g., strength and permeability). The ability of
jet grouting to solve multiple problems with a single elegant solution often creates
room for economic savings and elevates it as a technically superior option.
3.4.2 Wide range of soil applicability
The most outstanding feature of jet grouting is its ability to uniformly mix cement
grout with a wide range of soils. Its flexibility derives from its unique property of de-
stroying the soil fabric before grout is introduced; soil structure is not as significant a
factor as in other injection or permeation grouting methods. Jet grouting can be em-
ployed in most soil types (cohesive or granular) and stratigraphy.
3.4.3 Low space requirements
The relatively small size of jet grouting equipment means the method may be used in
situations of limited area or headroom. This is important in underpinning applications,
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which frequently take place in urban settings with limited free space. Furthermore, it
should not be overlooked that the treatment of a relatively large area of soil (columns
up to one or two meters in diameter) can be accomplished with only a small borehole
(with diameters of 10 to 20 cm) drilled into the ground.
3.4.4 Minimal site disturbance
Minimal noise and vibration occurs during jet grouting. Little settlement or heave
occurs as spoils are constantly removed from the borehole.
3.4.5 Abili ty to bypass buried obstructions
As the process relies on breaking down soils into slurry form before grout is mixed in,
jet grouting can work around buried obstructions such as boulders, utilities, pipelines,
etc. and incorporate these into the eventual grouted mass. Soil around these obstruc-
tions are fluidized by the erosive jet and mixed with grout. In this manner, buried ob-
structions which are not able to be eroded are bypassed, in the process becoming em-
bedded in the soilcrete to form part of the structural system.
3.4.6 Controllabili ty, predictabili ty, and automation
In comparison to other grouting methods, jet grouting may be considered relatively
controllable. The high-pressure water and cement jets are able to accurately cut and
erode the soil within a radial zone. Adjustment of various operational parameters (e.g.,
rotation and lift rate of drill rod, pressure and volume adjustments of grout and water)
can be automated as well to improve reliability. The feedback from pressure gauges
and other instruments can be used to make real-time adjustments to ensure a consis-
tent quality of soilcrete.
3.4.7 Flushing requirements
One of the disadvantages of jet grouting methods is that continuous flushing must be
maintained. If clogging occurs, significant pressures may build up rapidly and cause
heave and fracturing in the soil. Also, as the jet grouting is a high velocity method, a
large volume of spoils must be handled.
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3.4.8 Costs
Jet grouting may be considered expensive relative to some other methods. As men-
tioned before however, the methods ability to solve multiple problems may render it
an economic (although still expensive) option in certain situations.
3.5 Developments
As with many other geotechnical methods, research on jet grouting is still ongoing as
people search for improvements and better understanding. Schaefer (1997) describes
several developments which are relatively new in the field.
3.5.1 Super jet grouting
Recall the earlier discussion of increasing fluid energy by boosting the grout flow rate.
High grout flow rates have been used to create new jet grouting systems capable of
column diameters up to five meters.
3.5.2 Cross jetting
Instead of using a single water jet for cutting, two water jets inclined slightly so they
intersect at some distance away from the drill rod are used (see Figure 8). At the point
of intersection, the fluid energy of the colliding jets dissipates rapidly and effectively
terminates the jets for better diameter control.
Figure 8. Collision jet for soil cutting (from Shroff and Shah 1999).
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3.5.3 Mechanical mixing and jet grouting
Jet grouting has been adapted to mixing blade systems so that hydraulic erosion com-
pliments the mechanical mixing action (see Figure 9). The hybrid system is intended
for use in ground stabilization applications where large clear swathes of land need to
be treated.
Figure 9. Mechanical jet combined method (from Shroff and Shah 1999).
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4 JET GROUTING PRACTICE
4.1 Introduction
A complete jet grouting program involves many steps before, during, and after the
grouting works. As with any geotechnical problem, a preliminary site investigation
should be performed to ascertain the soil properties of the area. The information can
then be used to select the appropriate materials and equipment, as well as to design
operational parameters. As grouting works progress, continuous monitoring of operat-
ing variables is necessary to ensure that everything goes as expected. Finally, after the
grouting is complete, tests are carried out to check that the soilcrete meets perform-
ance specifications.
4.2 Equipment
Jet grouting equipment may be divided into two parts: a fixed station which prepares
the grout and a mobile rig which performs the grouting (see Figure 10). A typical sta-
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tion consists of cement storage, a mixing plant, and a high pressure pump. For dou-
ble- and triple-fluid systems with air and water components, additional equipment and
storage for those fluids may be present (e.g., water storage, air compressor). The rig
unit consists of a wheel- or track-mounted body with a drilling rod attachment (see
Figure 11). The rod contains the pipelines which convey the high-pressure grout, air,
and water. At the end of the drill string, there is a section called the monitorwhich
contains the nozzles.
Figure 10. Schematic view of jet grouting equipment (from Shibazaki and Ohta 1982).
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Figure 11. Typical track-mounted jet grouting rig (from USDOE 1998).
4.2.1 Pre-drilling versus self-jetting setups
Before grouting can be performed, a borehole must be drilled in the ground. This is
commonly accomplished either by drilling and switching to a grouting rig, or in one
step via a self-jetting setup. A self-jetting setup is one in which a pressurized water jet
ejected from the bit is used to excavate the hole in the ground. After jetting to the re-quired depth, a check ball (a spherical valve device) or some other special valve may
be used to block off flow to the bit and redirect water to the side nozzles.
4.2.2 Monitor and nozzle properties
The monitor is the section which contains the grout, water, and air nozzles. It is lo-
cated at the end of the drill string right before the bit. In triple-fluid systems, the dis-
tance between the water and grout jets is referred to as the monitor height. This dis-
tance has significant implications on the properties of the eventual soilcrete; smaller
heights lead to a higher degree of mixing and larger heights lead to a higher degree of
replacement (Covil and Skinner 1994).
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Nozzle characteristics are also important factors which affect grouting performance.
Shibazaki and Ohta (1982) have noted that the shape and dimensions of the jet noz-
zles are extremely important in maximizing the energy of the water jet. The nozzle
length and angle are particularly important to ensure that the water stream does
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