choi-review on the jet grouting method

8/13/2019 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 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.

-

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

choi-review on the jet grouting method

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