2.4 .JET GROUTINGINTRODUCTIONJet grouting as a soil improvement technique is currently utilized throughout the world From its conception in Japan in 1973 (Yahiro and Yoshida 1973) its use has spread. first to Europe, then to South and North America, the Far East, Asia, and Africa The system of using hydraulic energy to erode the ground is now being extended to other applications and is being used in conjunction with other techniques for better control of the improved soils Jet grouting offers a unique degree of design flexibility for a wide range of soil conditions and for a broad range of applications. These include working in and around sensitive structures where property and personnel safety are imperative.

Jet grouting can be defined as a method based on the introduction hydraulic (sometimes combined with pneumatic) energy in order to erode soil and mix/replace the eroded material with an engineered grout to form a solidified in situ element known as Soilcrete The elements are most often interconnected to provide underpinning to structures, excavation support, groundwater control, or in soil stabilization for a variety of civil and environmental applicationsPrior to Soil İmprovement-A Ten Year Update (Welsh 1987), only a very few jet grouting projects were completed in the United States (Langbehn 1986. Andromalos and Gazaway 1986) Indeed, the conference itself included no U.S. jet grouting case histories Since that time, well over 150 projects have successfully utilized jet grouting methods Many of these projects have been documented. A selection of readily available North American publications is provided in a chronological bibliography at the conclusion of this section of the report, the better to illustrate the progress of the jet grouting time line since 1987. Many more publications exist internationally.

Table 24-1 below places those U.S publications into the five broad application categories previously discussed This serves as very substantial support from the engineering and construction community that jet grouting offers a system suitable to many applications and a wide variety of soil types and stratigraphy.

FUNDAMENTAL CONCEPTSAs shown in Fig 24-1, there are three basic styles of jet grouting (Burke and Mellc I <)91 ) There has been much discussion over the years related to jet grouting being a high pressure grouting system This is not at all correct and warrants review. For each system, in situ erosion of soils occurs by impact energy from a high velocity fluid stream(s) Note that the velocity of the fluid is created by pumping pressure forcing it through a small nozzle(s) The distribution of fluids injected into the ground is through a "monitor" located at the end of the drill string, but just above the drill bit The drill bit is sized larger than the drill string and monitor, permitting return of slurry up the annulus between the drill string and the borehole wall at a rate sufficient to carry soil cuttings and to ease ground penetration If any pressure results during the erosion process of jet grouting, it is immediately relieved via the drill annulus

Table 24-1 Jet grouting applications

Application Chronological Bibliography NumberExcavation Support/Underpinning 4,5,6, 7,9, 12, 14,15, 16, 17,20,21,28,29,31,34,36,37,39,43,44,46Groundwater Control 4,5, ] I, 17,19,25,28,30,34,35,37,39,40,42,43Tunnel/Ground Stabilization 1,3,4,5,8, 13, 15,26,29,34,37,38,39,41,44,45,47Piling/Anchoring 5,27,37,39Environmental Applications 24,27,29,30,32,33,37,39,42

In fact, the European code of practice for jet grouting supports the need to assure a continuous flow of spoil return to the surface during jetting It is very important to understand that control of the return spoil ensures pressure control of the in situ erosion environment so that no energy is wasted hydrofracturing the soil in lieu of eroding the soilQuality jet grouting is reliant on continuity of erosion parameters and controlling the erosion environment This is particularly so when the inspection issues are nearly all procedural and repetition is all importantDifferent soil types exhibit different erodibility characteristics (Fig. 2.4-2).

Cohesionless soils are relatively easy to erode as they have no binder (other than moisture) and are actually self erosive when subject to such a turbulent environment At the other end of the scale, clays are difficult to erode as they are bound by cohesion It should be noted here also that up-hole velocities are not generally great enough to exhaust particles larger than a fine sand size. Plastic clays, fo, example, will generally break in chunks and pieces rather than small particles, and this often causes annulus plugging and spoil return loss This could be cause for hydrofracturing and poor control of Soilcrete quality and geometry. Spoil return can be assisted by multiple nozzles, air sheathing the jet nozzle(s), multiple directions of the nozzles, drill casing, auxiliary air injected above the monitor, multiple cutting lifts, or combinations of the aboveOnly specialist experience is currently available to assess which system, method, and procedures will furnish the Soilcrete that achieves the project goals, and in general, more than one system can usually be utilized

CURRENT DESIGN PRACTICEUnderpinning is the application for which jet grouting has been most used in the U.S. This is probably due to the cost and schedule competitiveness of the system, as well as the safety of jet grouting versus conventional systems. This is particularly so when underpinning is also combined with excavation support and groundwater control In general, underpinning design focuses on developing a geometry of interconnected Soilcrete which is capable of resisting overturning and sliding (Fig 2.4-3). The Soilcrete geometry is assumed to act as a homogenous mass not unlike a gravity wall Internal stresses are usually checked at critical locations, and the average desired unconfined compressive strength is typically set at three times the design requirements

Where groundwater control alone is required, Soilcrete permeability and wall thickness is usually set Permeability is one of the most difficult parameters to test for in the field, and has resulted in quality concerns on more than one project. Occasionally, modulus is also a criterion, depending on design deformation requirements.

For tunnel stabilization, a strength criterion is all that is usually desired, along with a somewhat homogenous Soilcrete matrix This is the case in microtunneling and tunnel boring machine work where groundwater intrusion and face stability are serious problems On at least one occasion in the US, nearly horizontal jet grouting has been applied to create a tunnel roof structure (similar to forepoling). This has proven successful in Europe when applied to the New Austrian Tunneling Method in unsaturated ground

CONSTRUCTION METHODS AND MATERIALSIn general, all systems of jet grouting have similar basic constructionprocedures

1 Set up on location at design angle of penetration2 Drill to depth by hydraulic rotary methods3 Commence jet grouting at the base of the design depth, lifting (and rotating if

required) uniformly until the design top is reached

Many variations to these procedures have been developed to overcomedrilling difficulties or ensure waste return These includeAccess: Pre-drilling, cased hole drilling, using a Down-the-Hole hammer

beneath the monitor, high flow drill fluid injection, high pressure drillfluid injection and drill fluid variations

Erosion: Precutting, double cutting, multiple nozzles, angled nozzles, auxiliaryair nozzles, high pressure air, increased high pressure fluid, ultra-highpressure of fluid injection, and relief hole placement

The equipment to perform jet grouting remains specialized, but a sufficient number of vendors are available Drills range from miniature, electrically powered units to large crane supported systems Some drills have the ability to create a wide variety of Soilcrete geometries through specialized controls for rotation and lift (Fig. 24-4)

Pumping systems are also specialized, and usually range from 300 to 500 Horsepower Most triple system pumps are containerized so that the three parameters (air, water, grout) are centrally controlled and monitored.

Slurry preparation can be very simple, manual mixing or it can be highly automated. This is so for both batch system mixing or continuous jet mixing operations. In any case, jet grouting requires the ability to batch slurry at a rate of 5 to 25 m3/hr ( 6 to 32 yd3/hr), depending on the system applied, at specific gravities:; of 1.4 to 1.8.The sequence of Soilcrete production is an important factor in the production of quality Soilcrete. This is a consideration for all jet grouting projects, but particularly when the application includes underpinning.

The work plan for jet grouting is also important and is somewhat integrated into the sequence of operations A few things to note here:*angle jet grouting beyond 30° from vcrtical should nul u:;c air as a component, as it tends to fracture the ground and cause heave*always consider work to be done in a primary, secondary, tertiary, etc sequence*in general, work should progress from low in situ stress regions to high in situ stress regions; that is to say, when underpinning, start beyond the edge of a column footing and progress daily closer to the center until the design coverage is achieved. This will allow soil to "arch" and minimize structure deformations until the Soilcrete cures sufficiently to accept load.

Jet grouting materials typically use blends of water and cement. It has been found that a variety of cement additives are usefully applied to delay set, reduce shrinkage, reduce permeability, ease equipment cleanup, and improve pumpability Slag cements, fly ash, and swelling clays have also been used successfully Future environmental applications will include specially developed materials for very low permeability, chemical reactivity in permeable walls, or to increase permeability for selective groundwater control.

QUALITY CONTROL/QUALITY ASSURANCEThe basic method of jet grouting construction is procedural; that is to say that one should maintain the jet grouting parameters and materials consistent with the approved test section The need for installing test elements of Soilcrete and checking for quality and geometry, prior to production work remain a necessity. Unless one has worked at the specific site before, it is not possible to predict jetgrouting parameters with precisionIt is however, possible to estimate these valuesempirically from past experience in similar conditions These parameters include:

Drilling Bit (hole) diameter, drilling slurry makeupDrill Settings Lift speed, rotation speed, number of liftsMonitor Nozzle/port si7es for all components injected, angle of the nozzle( s ),

number of nozzlesInjection Volume and pressure of all components injectedMaterial Method of mixing and material components and their concentration(s)

In some cases, grout mixes should be tested in the laboratory to ensure that the quality desired can be achieved Ordinarily, this can be predicted with reasonable accuracy by knowing the material type and amount of cement injected. Kauschinger (Kausehil1ger et al l992) identities a useful method to evaluate in situ cement contentAdditionally, by measuring waste return unit weight one should be able to assess geometry of Soilcrete However, this geometry prediction method has not proven reliable, and coring/excavation remains the best method to assess geometry.

Over the past ten year, a variety of methods to sample and test Soilcrete have been developed as shown in Table 24-2Devices have been developed to retrieve wet grab samples at any depth, provided the sampler can be inserted in the uncured Soilcrete to the depth desired, If the ground is very sandy and/or includes cobbles and boulders, this

will restrict deep insertion Wet grab samples are usually poured into small molds and cured and tested like a concrete cylinder

Table 2 Sampling and Tcsting MethodsRequirement Sample Method(s) Test MethodsStrength Wet grab (in situ) cast in Unconfined Compression

to molds TriaxialCast in place plastic pipe Tensionretrieved after cure Direct ShearCore drilling CPT (in situ) if soft enough

Permeability As above plus PermeameterCast-in-Place Piezometer Rising or Falling HeadDrilled and cast (in situ)Piezometer Packer Testing

When permeability is a requirement, that test method and its employment should be understood The only true method to test this is to perform pump testing in a Soilcrete contained soil "tub" It is nondestructive and reliable Cast-in-place piezometers have shown reasonable accuracy and have correlated well to wet sample results Packer testing relies on the assumption that Soilcrete can be cored nondestructively This has proven to be very difficult, and the results from packer tests have shown highly variable correlation to wet grab sample tests or in situ tests

NEW APPLICA TION OF JET GROUTINGAs previously shown in Table 24-1, and also discussed under current design practice, the majority of documented jet grouting applications to date have been for either underpinning, excavation support, or groundwater control. More recently, however, jet grouting technology has been used to meet all three of these traditional requirements in a single project, and has also been applied in other, less traditional areas with considerable success, paving the way to even wider acceptance and usage in the future

Virginia Key Waste Water Treatment Plant, Virginia Key, FloridaPrior to incorporation of a storm surge pressure relief system into an existing outfall pipe, all three project requirements of underpinning in-place utilities, excavation support, and groundwater control were able to be met by jet grouting Subsurface investigation had determined 58 m (19 ft) of loose to medium dense sand with peat inclusions overlaying weathered limestone and limestone bedrock Groundwater was at 091 m (3 ft) As shown in Fig 24-5, triple-rod jet grouting was performed at eachend of the excavation area adjacent to and below the 2.6 m ( 85 fi ) diameter pipe down to bedrock. Angled drilling and jet grouting beneath the pipe invert completed the encapsulation, thus froming a groundwater seepage barrier as well as excavation support and underpinning across the width of the excavation. Sheet piles connected the sides of the excavation with the grouted zones.

Nimitz Relief Sewer, Honolulu, HawaiiAs a value-engineered and less disruptive alternative to open cut construction, jet grouting provided a homogenized tunnel horizon for the installation of a 1.4 m (4.6 ft) relief sewer through soft, lagoonal deposits. Two rows of 1.2 m ( 4 ft) diameter, interconnected Soilcrete columns were installed over 800 Im (2600 If) of tunnel alignment to prepare an encapsulated horizon for micro-tunneling. Alternate columns extended to coral formation bedrock at an average depth of 6.7 m (22 ft) below grade, while intermediate columns terminated at 091m (3 ft) below tunnel invert (Fig. 2.4-6). This design provided a fully stabilized tunneling face and mitigated the potential for post -construction settlement

Philadelphia International Airport, Philadelphia, PennsylvaniaBefore construction ofa portion of the airport's new commuter runway over a former Superfund site, additional site remediation was needed to meet U.S Environmental Protection Agency final closure requirements The site, previously used to dispose of solid waste incinerator ash and other hazardous materials, was clay capped in the 1980's, In order for Philadelphia's Division of Aviation to use the site, a closure plan was developed, one component of which was the installation of a low permeability horizontal barrier above a very thin natural clay stratum underlaying approximately 1020 m2 (11,000 ff ) of the 150,000 ~ (37 acre) landfill footprint The new barrier was constructed using double-rod jet grouting techniques to excavate and replace the bottom 091m (3 ft) of the waste mass with a grout specially formulated to meet the low permeability, low elastic modulus and compressive strength requirements of the project design As shown in Fig. 2.4- 7, jet grouting ensured the minimum 152 m (5 ft) barrier needed to comply with closure specifications

NEW DEVELOPMENTSLike other ground treatment methods, jet grouting has evolved and, along with the new applications described above, new enhancements continue to be applied. Most of these have come from Europe and Asia, where the system has significantly longer history, but a few have been initiated in the US

1. Sacrificial Casing: This is the use of pre-installed sacrificial plastic casing to aid in controlling spoil return and maintain a consistent grouting environment (Viner and Wooden 1990) This thin wall PVC casing is weakly grouted in a predrilled hole, and when Jet grouting commences is blasted into small pieces by the cutting jet

while acting as a stable borehole to permit ease of return spoils, This is particularly helpful for near-horizontal works, but may be applied in future work for deep applications [>25m (82 ft)]

2. Anchorage Applications: In Europe, the jet grouting system has been employed to effect higher anchor capacities in weak soils (Ground Engineering 1988} Jet grouting for the bond zone creates a large bond area, and provided grout quality is high enough, permits transfer of higher friction capacities from the soil to the anchor

3. Super Jet Grouting: Where soil stabilization of soft soils is necessary, jumbo jet grouting has been effective This is similar to Triple System jet grouting, except that the erosion energy is boosted by increasing the volume of the jetted fluid. This is coincident with a grout rate boost to stabilize these large diameter elements which can reach 5m ( 164 ft)

4. Cross Jetting: In an effort to better control quality and geometry cross jetting has been developed (Shibazaki, Yoshida and Matsumoto 1996) This technology uses a pair of water/air nozzles aligned to intersect at a specific point At this point, the fluid impact quickly dissipates the energy. With slow, consistent rotation and lift, a controlled geometry is eroded, and thus a design grout injection can be made providing a higher degree of Soilcrete quality and consistency.

5. Directional Drilling combined with Jet Grouting. This variation of single system jet grouting is currently being experimented with in Europe It has application in providing horizontal barriers for groundwater or leachate control

6. Combined Mechanical Mixing and Jet Grouting Applying jet grouting to mechanical systems provides the addition of hydraulic erosion energy to the mechanical mixing energy (Miyoshi and Hirayama 1996) As a growing ground treatment system in Japan, it is expected to be applied more widely as a ground stabilization system.

CONCLUSIONSThe next ten years of jet grouting are expected to expand on these new developments Additionally, new grout materials will be introduced to enhance Soilcrete quality, and applications for environmental remediation are inevitable Present practice will continue to grow as the engineering community learns more about the variety of applications for jet grouting and its effectiveness.

CHRONOLOGICAL BIBLIOGRAPHY OF READILY AVAILABLE

PUBLICATIONS ON U.S. JET GROUTING: 1986 -1996Refer to Table 2.4-1 for corresponding applicatioQ1. Langbehn, W.K. (1986) "The Jet Grouting Method. Applications in SlopeStabilization and Landslide Repair." Master of Engineering Report, Department of Civil Engineering, University of California, Berkeley, CA2. Andromalos, K.B., and Gazaway H.N. (1986) "Jet Grouting Snail's Pace of

AdoptioQ" Civil Engineering, December, 40-43.3. Bruce, DA, Boley, D.L, Gallavresi, F (1987). "New Developments :~Ground Reinforcement and Treatment for Tunneling" RETC, VoI. 2, 81835.

4. Guatteri. G., et al (1988) "Advances in the Construction and Design of Jet Grouting Methods in South America." Proceedings of the Second International Conference on Case Histories in Geotechnical Engineering, St Louis, MO.

5. Pet tit, P., and Wooden, C.E. (1988). "Jet Grouting. The Pace Quickens." Civil Engineering, August, pp. 65-68.

6. Rosenbaum, D.B (1989). "Sugar Sands Stabilized Safely." Engineering News Record, February 9, p. 187. Burke, G.K., Heller, RA., and Johnsen LF (1989). "Jet Grouting for Underpinning The Cutting Edge."

Geotechnical News, March" Vol 7, No.1, pp. 25-28.8. Battista, D., et al (1989). "Jet Grout Stabilization of Peaty Soils Under a Railway Embankment in Italy."

Foundation Engineering: Current Principles and Practice, ASCE Geotechical Special Publication No.22, Vol 1, pp. 272-290.

9. Burke, G.K., et al (1989). "Jet Grouting for Underpinning and Excavation Support." Foundation Engineering: Current Principles and Practice, ASCE Geotechical Special Publication No 22, Vol 1, pp 291-300.

10. Andromalos, KB and Gazaway, H.N (1989). "Jet Grouting to Construct Soilcrete Wall Using a Twin Stem System" Foundation Engineering: Current Principles and Practice, ASCE Geotechical Special Publication No. 22, Vol 1, pp. 301-312.

11. Garner, S.J., et aI (1989). "The Application of Flexible Jet Grout tor a Cutoff at John Hart Dam." Proceedings of the 42nd Canadian Geotechnical Conference, pp 249-256

12. Kauschinger, J.L., and Welsh J.P. (1989). "Jet Grouting for Urban ConstructiOQ" Geotechnical Lecture Series: Design Construction and Performance of Earth Support Systems, Boston Society of Civil Engineering, Massachusetts Institute of Technology, Cambridge, MA

13. Stella, C., et al (1990). "Temporary Tunnel Support Using Jet-Grouted CylInders." Journal of Construction Engineering and Management, ASCE, Vol. 116, No.1, pp. 35-53.

14. "Lake Placid's Luge Run Undergoes Jet Grouting" (1990). CivilEngineering, News Section, June, pp. 27-28.

15. Viller, RL and Wooden, C (1990) "Jet Grout Underpinnillg ofthc NewJersey Avenue Sewer" Proceedings of the International ,)ympo.\,illlll on Uniqlle Undergrollnd ,)troctllre\", Denver, CO, June, 89-1 to 89-1916 Burke, GK, and Metre, DA (1991) "Fixing Foundations: ('i\'il

Engineering, March 1991,63-6517. Burke, G.K., and Welsh J.P (1991) "Jet Grout Uses for Soil

Improvement." Geotechnical Engilleering Congress, ASCE GeotechicalSpecial Publication No 27, Vol1, pp 334-345

18 Patel, A and Castelli, R (1992). "Permanent Slurry Walls at BaltimoreMetro's Shot Tower Station" Slurry Walls: Design and Constroction and Quality Control, Paul, Oavison al!d Cavalli, Eds, ASTM, STP 1129, American Society for Testing and Materials, Philadelphia, PA, pp 403-41919. Miyasaka, G., et al (1992) "Jet Grouting for a Self Standil!g Wall"Grollting, Soil Improvement and Geosynthetics, ASCE Geotechical Special Publication No. 30, Vol1, pp. 144-15520. Parry-Davies, R, et al (1992) "Stabilization of Picr Foundation Using jetGrouting." Grollting, Soil Improvement and Geosynthetics, ASCE Geotechical Special Publication No 30, Vol1, pp 156-16821 Kauschinger, JL, Perry, E.B., and Hankour, R (1992) "Jet Groutillg State of the Practice" Grollting, Soil Improvement and Geosynthetics, ASCE Geotechical Special Publication No.30, Vol 1, pp 169-18122. Ichihashi, Y, et al ( 1992) "Jct Grouting In Airport ConstructioQ"Grouting, Soil Improvement and Geosynthetic.l., ASCE Geotechical Special PublicationNo 30, Vol1, pp. 182-19323. Kauschinger, JL., et al (1992) "Methods to Estimate Composition of JetGrout Bodies: Grollting, Soi/ Improvement and Geosynthetics, ASCE Geotechical Special Publication No 30, Vol 1, pp 194-20524. Gazaway, HM. and Jasperse, B (1992) "Jet Grouting in ContaminatedSoils." Grollting, Soil Improvement and Geosynthetics, ASCE Geotechical Special Publication No.30, Val 1, pp 206-21425. Steiner, W., et a! (1992) "Soilcrete Cut-OtrWall for Undercrossillg a BusyRail Lille" Grouting. Soi/ Improvement and Geosynthetics, ASCE Geotechical Special Publication No 30, Voi 1, pp 384-39726 Ciallavrcsi, I' ( 1992) "Grouting Improvement of Foundation Soils,"Grouting, Soil Improvement and Geosynthetics,\" ASCE Geotechical Special Publication No 30, Vol I, pp 1-3827 Soil Washing lJS Patent No 5,098,224 Process and Device for the

Decontamination of Contaminated Sites28 Koelling, MA, and Ringen, A.R (1992). "Jet Grouting -Soil Improvement

Case Histories: Proceedings of the 28th Symposium on EngineeringGeology and Geotechnical Engineering, Boise, Idaho.

29 Flick, LD, et al (1992) "Minipile Milestone in Memphis: CivilIl;ngincering, September, pp 46-49

30 Burke, GK ( 1992). "In Situ Containment Barriers and Collection Systemsfor Environmcntal Applications: ,)ympo,\,illm on Design and Construction ofSllirl:y rValk, Canadian Geotechnical Society, Toronto

31 Burke, GK and Brill, G T ( 1992) "Foundation Stabilization SystemsUsing Jet Grouting Techniques" Proceedings of the Ohio River Valley

SCIllinar X,'(III, Louisville, KY32 Van Hoesen, SD, et al (1992). "White Oak Creek Embankment SedimentRetention Structure The Oak Ridge Model in ActioQ" Proceedings of Eighth Amlllal Oak I~idge Model Coliference on Waste Management and Environmental I~estoration, Oak Ridge, TN33 Harris, D, Woodcn, CE, and Motl, GP (1992) "Application of JetGrouting as an In Situ Technology for the White Oak Creek Embankment Time Critical Removal Action: Proceedings of Eighth An mia/ Oak Ridge Model Coliference on rVaste Management alld Environmenta/ Restoration, Oak Ridge, TN:34 Moseley, MP, Editor (1993) Grollnd Improvement, CRC Press Inc., Boca

Raton, l'135 Burke, GK and Brill, G.T (1993) "Anchored Cutoff Design and.Construction" Proceedings of the Third International Conference on Care Hi.\'torie.l. in Geotechnical Engineering, University of Missouri-Rolla, pp. 1313-131836 Scarborough, JA, Boehm, OW, al!d Brill, GT. (1993). "The Use ofJetGroutil!g for Undcrpilll!il!g al!d Temporary Excavation Support of a Historic Building" Proceedings of the Ohio River i/alley Soils Seminar XXIV, Cincinnati, Ohio

37. Bruce, D.A, (1994 ) "Jet Grouting: Gro1ll1d Col1lrol {I/Id I111prove111el1l,Xanthakos, Abramson and Bruce, Eds, John Wiley and Sons, Inc, New York, NY, pp580-68338 "Safety Issue Boosts Record Soft Ground Jct Grouting Job" ( 1990) (:ivil

El1gineerillg, News Feature, October, 1994, 18-1939. Tarricone, P. (1994) "Jet Grouting Gains: Civil/~l1gil1eeril1g, Deccmbcr

1994, 40-4340 Welsh, J.P, and Burke, GK. (1995) "Vertical Cutoffs and Bottom Scaling"

Geoenviron111el1t 2000, ASCE Geotechical Special Publication No 30, Vol I,pp. 1207-1221

41. Edgerton, WW., Berti, D.J, Wong, MM (1995) "San Francisco CSO:Civil Engil1eerillg, May, pp 68-71.

42 Burke, G.K (1995) " Applying Jet Grouting Techniques to ConstructVertical and Horizontal Barriers: lIIterl1aliol1al Col1laill111el1t l"echl1olo/,'YWork.\.hop, Baltimore, MD.

43. Burke, GK and Koelling MA. (1995) "Special Applications for JetGrouting. Underpinning, Excavation Support and Groundwater Control" Proceedillgs of 48th Canadial1 Geotechnical Colljerel1ce, Vancouver, British Columbia, pp. 89-9744. no, C.E. (1995). "An Instrumented Jet Grouting Trial in Soft Marine Clay:Verification of Geolechl1ical Gr01ltil1g, ASCE Gcotechica! Special Publication No. 57, pp, 101-11545. Atwood, MJ. and Lambrechts, R. (1995) "A Test Program to VerifyGrouting Applicability for Boston's Central Artery Tunnel" r7erificatiol1 of Geotechnical Gr01llil1g, ASCE Geotechical Special Publication No 57, pp 78-100.46. Drooff, E.R, Furth, AJ, and Scarborough JA (1995) "Jet Grouting to Support Historic Structures: Foundation Upgrading and Repair for Infrastructure Improvement, ASCE Geotechical Special Publication No 50, pp 42-5547 Raines, GL, and Honke, JK (1996) "Honolulu's Street Relief" Civil

El1gilleerillg, September

REFERENCESMiyoshi, 1\, and Ilirayama, K (1996) "Test of Solidified Columns using a Combined System of Mechanical Churning and Jetting: Proceedings of IS/()J.\'O '91): jill! Sl!c()lld /,lll!maliolla/ Coi!fl!rel1ce 011 Grolmd Improvement (;eQ~Vme111s, Tokyo, pp 743- 748

Shiba7aki, M, Yoshida, 11, and Matsumoto, Y (1996) "Development of a Soil Improvement Method Utilizing Cross Jel" Proceedings of IS-Tokyo '96: 'lile Secol1d 1111erl1aliol1al COI!(erel1ce 011 Ground Improvement Geosystems, Tokyo, pp 707-710

Yahiro, T, and Yoshida, 11 (1973) "Induction Grouting Method Utilizing High Speed Water Jet: Proceedil1gs of the Eighth International Conference on Soil Mechal1ics al1d F01ll1datiol1 El1gil1eeril1g, pp 402-404,

" Jet Grouted Anchors Put to the Test," (1988) Gr01ll1d El1gineering, September, p. 16

Jet Grouting Jet grouting is the newest of the grouting methods and is rapidly becoming the most widely used. Jet grouting uses high pressure jets to break up the soils and replace them with a mixture of excavated soils and cement, typically referred to as "soilcrete". There are a number of variations of jet grouting depending on the details of the application and on the experience and expertise of both the designer and the contractor.

The design of a jet-grouted column is influenced by a number of interdependent variables related to in situ soil conditions, materials used, and operating parameters. Table 7-11 presents a summary of the principal variables of the jet grouting system and their potential impact on the three basic design aspects of the jet-grouted wall: column diameter, strength and permeability. Table 7-11 gives typical ranges of operating parameters and results achieved by the three basic injection systems of jet grouting. It should be noted however, that the grout pressures indicated in this table are based on certain equipment and can vary. This table can be used in feasibility studies and preliminary design of jet-grouted wall systems. The actual operating parameters used in production are usually determined from initial field trials performed at the beginning of construction.

Jet grouting is frequently used as a ground control measure in conjunction with tunneling in soft ground using Sequential Excavation Method (Chapter 9).

Table 7-11 Summary of Jet Grouting System Variables and their Impact on Basic Design Elements

Principal Variables

General Effect of the Variable on Basic Design Elements (Strength, Permeability and Column Diameter)

(a) Jet-Grouted Soil Strength

Degree of mixing of soil and grout

Strength is higher and less variable for higher degree of mixing

Soil type and gradation

Sands and gravels tend to produce stronger material while clays and silts tend to produce weaker material.

Cement Factor Strength increases with an increase in cement factor (weight of cement per volume of jet-grouted mass).

Water/cement ratio of grouted mass

Strength of the jet-grouted soil mass decreases with increase in in situ water/cement ratio.

Jet grouting system

The strength of the double fluid system may be reduced due to air entrapment in the soil-grout mix.

Age of grouted mass

As the jet-grouted soil mass cures, the strength increases but usually at a slower rate than that of concrete.

(b) Wall Permeability

Wall continuity Overall permeability of a jet grout wall is almost entirely contingent on the continuity of the wall between adjacent columns or panels. Plumb, overlapping multiple rows of columns would produce lower overall permeability. In case of obstructions (boulders, utilities, etc.) if complete encapsulations is not achieved

Table 7-11 Summary of Jet Grouting System Variables and their Impact on Basic Design Elements

Principal Variables

General Effect of the Variable on Basic Design Elements (Strength, Permeability and Column Diameter)

then overall permeability may be increased due to possible leakage along the obstruction-grout interfaces.

Grout composition

Assuming complete wall continuity and complete replacement of in situ soil, the lowest permeability which can be obtained is that of the grout (typically 10-6 to 10-

7 cm/sec). Lower permeabilities may be possible if bentonite or similar waterproofing additive is used.

Soil composition If complete replacement is obtained (as may be possible with a triple fluid system) then soil composition does not matter. Otherwise, if uniform mixing is achieved then finer grained soils would produce lower permeabilities as compared to granular soils.

(c) Column Diameter

Jet grouting system

The diameter of the completed column increases in size as the number of fluids is increased from the single to the triple fluid systems.

Soil density and gradation

As density increases, column diameter reduces. For granular soils, the diameter increases with reducing uniformity coefficient (D60/D10).

Degree of mixing of soil and grout