Use of Fully Grouted Method Barr Engineering

The Use of the Fully-grouted Method forPiezometer InstallationPart 1

Ivn A. ContrerasAaron T. GrosserRichard H. Ver Strate

IntroductionThe fully-grouted method described inthis ar t ic le entai ls instal l ing apiezometer tip in a borehole which isbackfilled entirely with cement-benton-ite grout. Part 1 of this article presents adetailed discussion of the fully-groutedmethod, including the installation pro-cedure and theoretical background, aswell as a seepage-model analysis usedto evaluate the impact of the differencein permeabilities between surroundingground and cement-bentonite grout.Part 2 describes laboratory test resultsfor six cement-bentonite grout mixesand field examples of applications ofthe fully-grouted method. Both parts ofthis article are based on the paper, TheUse of the Fully-grouted Method forPiezometer Installation, presented atFMGM 2007: Seventh International

Symposium on Field Measurements inGeomechanics, and are published inGIN with permission from ASCE.

A crucial parameter for the successof the fully-grouted method is the per-meability of the cement-bentonitegrout. Vaughan (1969) postulated thatthe cement-bentonite grout should havea permeability no greater than two or-ders of magnitude higher than the sur-rounding soil in order to obtainrepresentative pore-water pressurereadings. Unfortunately, there is limitedpublished data on the permeability ofcement-bentonite grout mixes.

Figure 1a shows the typicalpiezometer installation commonlyknown as a Casagrande or standpipepiezometer. With this installation, thetip of the piezometer (e.g., slotted PVCpipe or porous stone filter) is sur-

rounded with a high permeability mate-rial, commonly referred to as sand pack.Above the sand pack is a bentonite sealtypically consisting of bentonite chipsor pellets. The installation is finishedwith cement-bentonite grout to theground surface. This installation relieson a sizable intake volume and a narrowriser-pipe diameter to obtain a pore-wa-ter pressure reading in the riser pipewithout significant time lag (Hvorslev,1951).

With the development of diaphragmpiezometers (e.g., pneumatic and vi-brating wire), the method developed forstandpipe piezometers was used for dia-phragm piezometer installations(Dunnicliff, 1993). This has been acommon practice for decades and theresulting installation is shown on Fig-ure 1b. However, because of the

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30 Geotechnical News, June 2008

low-volume operation of diaphragmpiezometers, the sand pack around theinstrument tip is unnecessary, and thediaphragm piezometer can be installedin the borehole surrounded by ce-ment-bentonite grout. This procedure iscommonly known as the fully-groutedmethod (Mikkelsen and Green, 2003)and is shown on Figure 1c.

Fully-grouted MethodFigure 1c shows a piezometer installa-tion using the fully-grouted method, inwhich a diaphragm piezometer tip is setin a drilled borehole and entirely back-filled with cement-bentonite grout. Thefollowing is a detailed description of theinstallation procedure for a vibrat-ing-wire sensor t ip in typicalgeotechnical boreholes (i.e., 140 mm),including preparation of piezometer as-sembly and materials, grout mixing,piezometer construction, and theoreti-cal background.

Piezometer AssemblyConstruction of the piezometer assem-bly commonly begins with attachmentof the sensor tip to a sacrificial groutpipe. The sacrificial grout pipe, whichcan be either belled-end electrical con-duit or threaded PVC well casing, isgenerally constructed or laid out on theground in manageable lengths for han-dling. The piezometer location is se-lected by reviewing the soil stratigra-phy. The sacrificial grout pipe willgenerally extend to the bottom of theborehole for support; therefore, it is

possible to determine the location of thepiezometer tip from the top or bottom ofthe borehole since the pipe is left inplace.

After drilling a borehole, thepiezometer tip is attached to the groutpipe at the appropriate location. Forboreholes with a diameter of 140 mm, atypical grout pipe (such as 25.4-mm di-ameter PVC well casing) is used.Large-diameter or stronger grout pipemay be required for deeper installationswith higher pumping pressures.

The sensor tip, which has been satu-rated following the manufacturers di-rections, is typically set with the sensorin the upward position to minimize thepossibility of desaturation. The cableconnected to the sensor tip is attached tothe pipe at approximate intervals alongthe grout pipe, leaving some slack in theline. The grout pipe, sensor tip, and ca-ble are then lowered into the boreholewith the grout pipe placed on the bottomfor support. The piezometer tip is nowlocated within the desired monitoringzone. The cable is brought to the surfacewhere readings are taken with a readoutdevice.

One advantage of the fully-groutedmethod is that it can be used for installa-tion of nested piezometers. In a nestedpiezometer configuration, more thanone piezometer tip is attached to thesacrificial grout pipe. The authors havesuccessfully installed up to fourpiezometer tips in a borehole. Duringinstallation the drill casing should be re-

moved carefully to prevent damage tothe cables and the cables should be sep-arated around the grout pipe to prevent adirect seepage path along a bundle ofcables.

Another advantage of thefully-grouted method is the feasibilityof using a single borehole to installmore than one type of instrument. Forexample, the piezometer tips can be at-tached to an inclinometer casing, and asingle borehole is used for measuringboth deformation and pore-water pres-sures, resulting in reduced drillingcosts. However, the inclinometer casingjoints must be sealed. This techniquehas been used successfully by the au-thors on several projects.MaterialsThe cement-bentonite mixes describedin this article use Type I Portland ce-ment and sodium bentonite powdersuch as Baroid Aquagel Gold Seal orQuickgel. The water used in the mixesshould be potable water to prevent pos-sible interaction of chemical constitu-ents in the water with the cement-ben-tonite mixture.

Grout MixingThe mixing procedure described in thisarticle assumes the availability of a ca-pable drill-rig pump and a high-pres-sure, jet-type nozzle attachment on theend of a mixing hose. In most cases, thedrill-rig pump provides enough pres-sure for the jet-mixing required to ob-tain a desirable mixture. Other methods

Geotechnical News, June 2008 31


Figure 1(a). Traditional standpipe piezometer with sand pack.Figure 1(b). Diaphragm piezometer with sand pack.Figure 1(c). Fully-grouted piezometer. Figure 2. Schematic computer model to simulate seepage

around a fully-grouted piezometer (borehole not to scale).

may use actual grout-mixing plants.Generally, the cement-bentonite mix isprepared in a barrel or mud tank usingthe drill-rig pump to circulate the batchwith a suction hose and return line.Occasionally, a hydraulically-operated,propeller-type mixer is used. However,it has been the authors experience that,in some cases (depending on the mixviscosity, pump operability on the drillrig, or grout volume), the use of a groutmixer/pump may be required. Typicalbatch sizes are 200 to more than 2,000liters.

The mixing process begins withcalculation of the amount of grout re-quired to fill the borehole. A measuredquantity of potable water is pumpedinto the mixing barrel first and circula-tion begins. During circulation, the wa-ter and cement are mixed first so that thewater:cement ratio remains fixed andthe properties of the grout mix are morepredictable. The measured quantity ofcement is gradually added to the wateruntil both components have been thor-oughly mixed. This is the most impor-tant step in the mix preparation and runscontrary to the common practice ofmixing bentonite and water first. An ini-tial measured quantity of powderedbentonite, based on a mix design, isadded into the barrel near the jet streamto minimize the formation of clumpswithin the mix. Typically, additionalbentonite is added as mixing continuesto achieve a creamy consistency.Mikkelsen (2002) describes the consis-tency as drops of grout should barelycome off a dipped finger and shouldform craters in the fluid surface.

Piezometer ConstructionAt the completion of the grout-mixingprocess, and after measuring the finaldensity of the mix, the piezometer tipassembly is lowered into the borehole.In shallow boreholes (e.g., typicallyless than 30 m deep), grout is thenpumped into the borehole through thesacrificial grout pipe until it reaches theground surface. In deeper boreholes,staged grouting using multiple groutpipes or multiple port pipes may be re-quired so the piezometers are notover-pressurized during installation. Incased boreholes, the drill casing is

slowly retrieved so that no gap is left be-tween the top of the grout and the bot-tom of the casing. Typically, the entireprocess takes approximately one hourfor a 30-m borehole. The hole is typi-cally completed with concrete and aprotective top.

The field engineer should take pres-sure readings during and immediatelyafter installation. One benefit of vibrat-ing-wire technology is that readings canbe taken quickly. The readings obtainedduring grouting can be used to deter-mine if the device has beenover-pressurized during grouting. Themeasured pressures should approxi-mately correspond to the pressure ex-erted by the column of grout above thetip, provided the sensor and grout are atnearly the same temperature, astemperature equalization may take sev-eral minutes. However, with time, thispressure decreases as the cement-ben-tonite mix sets up and pore-water pres-sure readings are taken at the tiplocations. Typically, grout set-up takesone to two days.

Theoretical BackgroundMcKenna (1995) clearly describes thetwo basic requirements for anypiezometer to perform its function. Themeasured pore-water pressure must befairly representative of the actualpore-water pressure at the measurementlocation (i.e., small accuracy error), andthe hydrodynamic time lag must beshort. At first glance, it does not appearthat the fully-grouted method will sat-isfy these requirements. It would seemthat the cement-bentonite grout sur-rounding the tip might prevent thepiezometer from responding quickly tochanges in pore-water pressures in theground due to its low permeability. Onthe other hand, if the cement-bentonitegrout is too permeable to enhance shorthydrodynamic time lags, there wouldbe significant vertical fluid flow withinthe cement-bentonite grout column.

However, the fully-grouted methoddoes satisfy both of McKennasrequirements . A diaphragmpiezometer, such as a vibrating wirepiezometer, generally requires only avery small volume equalization to re-spond to water pressure changes (10-2

to 10-3 cm3), and the cement-bentonitegrout is able to transmit this small vol-ume over the short distance that sepa-rates the piezometer tip and the groundin a typical borehole. A practical way toreduce this distance is to set up the tipclose to the wall of the borehole by re-ducing the thickness of grout betweenthe tip and ground using pre-manufac-tured, expandable piezometer assem-blies.

Grout PermeabilityRequirementsVaughan (1969) introduced thefully-grouted method and developedclosed-form solutions which showedthat the error in the measured pressure issignificant only when the permeabilityof the borehole backfill is two orders ofmagnitude greater than the permeabil-ity of the surrounding ground. If thepermeability of the cement-bentonitegrout is lower than the permeability ofthe surrounding ground, measuredpressures will be without error. As a re-sult, for the fully-grouted method towork, the grout mix used to backfill theborehole must meet certain permeabil-ity requirements. A seepage model wasdeveloped by the authors to better un-derstand those requirements.

Computer ModelingA finite-element computer modelsimulating seepage conditions around afully-grouted piezometer installationwas used to evaluate the impact of groutpermeability on the accuracy of thepiezometer reading. The seepage modelwas conducted using SEEP/W, a com-puter-modeling program developed byGEO-Slope International.

Figure 2 shows the conceptualmodel developed to simulate the seep-age around a piezometer installed usingthe ful ly-grouted method. Theaxisymmetric flow model includes a7-cm radius, cement-bentonite-groutcolumn surrounded by soil of constantpermeability. The simulated ce-ment-bentonite grout column extends27.5 m and the soil layer extends 33 mbelow the ground surface with a radiusof 50 m. Underlying the soil, a sandlayer was incorporated to simulate thelower boundary conditions.



The seepage analyses were per-formed simulating upward and down-ward flow using two sets of imposedtotal head conditions (i.e., 10 and 20 m)that induce flow under steady-state con-ditions. This set of boundary conditionscorresponds to the one-dimensionalflow condition in the vertical direction.In all cases, fully saturated conditionswere used for all the materials in themodel. The error, , defined as the dif-ference in computed pore-water pres-sure between the soil and the grout, wasdetermined during each model run at

points in the soil and grout 20 m belowthe ground surface, as shown on Fig-ure 2.

Results of Computer ModelingSeveral model runs were made in whichthe permeability ratio, kgrout/ksoil, wasvaried from 1 to 107. Figure 3 shows theresults of the seepage simulations interms of the normalized error, i.e., di-vided by the pore-water pressure in soil,usoil, against the permeability ratio. Fig-ure 3 also shows that the normalized er-ror is zero for all practical purposes up

to permeability ratios of 1,000 fordownward and upward flow and the twosets of imposed total heads. As the per-meability ratio increases beyond 1,000,the normalized error increases up toabout 10 percent at permeability ratiosof 10,000. As the permeability ratiocontinues to increase to 107, the nor-malized error also increases up to about23 and 40 percent, respectively, for the10-m and 20-m imposed total heads.

In summary, the finite-element com-puter model revealed that the perme-ability of the grout mix can be up tothree orders of magnitude greater thanthe permeability of the surroundingground without introducing significanterror. This finding differs from previousassessments, which indicated that thepermeability of the grout mix shouldonly be one or two orders of magnitudegreater than the permeability of the sur-rounding ground. The minimum per-meabil i ty that is l ikely to beencountered in natural soils is on the or-der of 10-9 cm/s. As a result, the ce-ment-bentonite grout mix used in thefully-grouted method needs to have apermeability of, at most, 10-6 cm/s.

Part 2 of this article will discuss lab-oratory test results of six cement-ben-tonite grout mixes and field examples ofapplications of the fully-groutedmethod.



Figure 3. Normalized error versus permeability ratio.

The Use of the Fully-grouted Method forPiezometer InstallationPart 2

Laboratory Testing ProgramA laboratory testing program was de-veloped to evaluate the range in perme-ability and strength of cement-benton-ite grout for piezometer installationsusing the fully-grouted method. Thetest program was designed so that small

batches of grout could be mixed in acontrolled environment without largegrout-batch mixing equipment. Six mixdesigns were chosen to represent a widerange of values that would reasonablybe used on projects.

Sample PreparationMixing the grout used for laboratorytesting began with calculating the de-sired quantities of material and thenweighing individual portions of ce-ment, water, and bentonite. Additionalbentonite was prepared in anticipation

of adjusting the mix viscosity. Theproperties of the individual mix compo-nents used in the laboratory testing arelisted in Table 1.

To begin, the cement was added to

the water slowly while mixing. Thebenefit of adding the cement first in themixing process is that it ensures the cor-rect water:cement ratio before addingthe bentonite.

After the cement and water weremixed and the water-cement paste ap-peared uniform, which generally tookfive minutes, bentonite was slowlyadded to the bucket. The cement-ben-tonite grout was then mixed for approx-imately five additional minutes until itappeared uniform and did not containlumps. Viscosity was measured at vari-ous times during mixing to evaluate thecondition of the mix. Samples of the fi-nal mix were taken using plastic moldsand the density was measured.

After a short cure period, the sam-ples were carefully extruded out of theplastic molds and stored until the testdate. For the Unconfined CompressiveStrength testing (UCS), a set of twospecimens were tested at 7, 14, and 28days. Permeability testing was com-pleted on specimens from each mix at 7and 28 days under three different con-fining stresses. In addition to strengthtests, basic index properties, such asmoisture content and dry density of thesamples, were also measured.

Laboratory Test ResultsTable 2 summarizes the final ce-ment-bentonite grout proportions usedin this study. The results of the labora-tory testing are presented in a series offigures.

Figure 4 summarizes test results asthe average UCS at 28 days versus thewater:cement ratio by weight. It showsthat the UCS decreases with increasingwater:cement ratios. In fact, the UCS at28 days is approximately 1700 kPa at awater:cement ratio of 2:1; it then de-creases to approximately 90 kPa withincreasing water:cement ratio. Also in-cluded on Figure 4 are data presented byMikkelsen (2002), which show a rela-tively strong correlation with the data ofthis study.

The void ratios of the samples werecomputed based on the measured watercontent of the specimens and the spe-cific gravity of the grout-mix constitu-ents. The computed void ratios of themixes are relatively high, in fact, theseare higher than soils with similarstrength and permeability. However, thedata show that the amount of cementcontrols the strength characteristics ofthe grout mix. Bentonite appears to in-



Table 1. Properties of grout constituents

Mix Component Brand Specific Gravity MoistureContent (%)

Portland Cement Type I LaFarge 3.15 Bentonite Quickgel

(Mixes 1-4)Baroid 2.41 to 2.45 11

Aquagel Gold Seal Ben-tonite (Mixes 5 and 6)

Baroid 2.4 10

Table 2. Summary of cement-bentonite grout mixes used in the study

Mix Water : Cement :Bentoniteby Weight

Marsh FunnelViscosity (sec)

Bentonite Type

1 2.5 : 1: 0.35 50 Quickgel2 6.55 : 1: 0.40 54 Quickgel3 3.99 : 1: 0.67 60 Quickgel4 2.0 : 1: 0.36 360 Quickgel5 2.49 : 1: 0.41 56 Aquagel Gold Seal6 6.64 : 1: 1.19 60 Aquagel Gold Seal

Figure 4. Variation of unconfined compressive strength versus water:cementratio.

fluence the amount of bleed water andvolume change of the specimen duringcuring. Additional information on thestrength and deformation properties ofcement-bentonite mixes can be found inContreras, et al. (2007).

Figure 5 summarizes the test resultsin terms of the permeability of the spec-imens at seven days for various confin-ing pressures. The data show thatsamples with a higher water:cement ra-tio or void ratio have higher permeabil-ity than those with lower water:cementratios.

Figure 6 shows the permeability in

the same format for specimens at 28days. Data are very similar, showingthat the permeability is relatively con-stant or decreases slightly with confin-ing pressure. One important result isthat, from seven to 28 days, the perme-ability continues to decrease. For exam-ple, mixes with 2.49 water:cement ratioindicate a permeability greater than1.0x10-6 cm/sec at 7 days and less than1.0x10-6 cm/sec at 28 days. The data in-dicate that, as hydration of the cementoccurs, the permeability of the mix de-creases. The high void ratio and lowpermeability are two reasons the

fully-grouted method works; it allowstransmission of a low volume of waterover a short distance yet maintains over-all low permeability in the vertical di-rection.

Figure 7 shows the variation in per-meability data with respect to void ratio.The data indicate that specimens withlower void ratios typically exhibit lowerpermeability, while those with highervoid ratios exhibit higher permeability.With grout mixes, the cement has agreater influence on the void ratio thanthe bentonite and is considered the con-trolling factor in the permeability of thegrout. The difference between the sevenand 28-day permeability is relativelysmall, as shown on Figure 7.

Field ExamplesThis section describes three field exam-ples in which the fully-grouted methodwas successfully applied. The first ex-ample compares pressure readings be-tween one installation using thefully-grouted method in a nested con-figuration and the traditional approachwith individual piezometer installationsin separate boreholes. The second ex-ample descr ibes use of thefully-grouted method with the installa-tion of nested piezometers in an up-ward-flow condition. The third exam-ple is for a nested, fully-grouted methodinstallation in a downward-flow condi-tion.

Example 1. Comparison BetweenNested and Individual InstallationsThis field example compares two meth-ods of installation: Three vibrating-wire piezometers in

a single borehole using thefully-grouted method.

Four individual pneumaticpiezometers in separate boreholesusing the traditional sand packaround the piezometer tips.The two installations were within 7.5

m of each other. As a result, some differ-ences in the pressure readings were ex-pected. Figure 8 shows a comparison ofthe pore-water pressure profile with ele-vation for both installations. The figureillustrates a fairly similar response con-sidering the distance between the twosets. Similar data have been presented



Figure 5. Variation of permeability versus confining pressure at 7 days.

Figure 6. Variation of permeability versus confining pressure at 28 days.

by McKenna (1995) , fur therconfirming the val idi ty of thefully-grouted method.

Example 2. Upward-FlowConditionsThis field example illustrates the use ofnested piezometers using thefully-grouted method in upward-flowconditions. The site is in an area wherethree distinct stratigraphy units arefound (alluvial deposits, Huot Clay For-mation, and Red Lake Falls Formation).The upward-flow conditions play a ma-jor role in the slope instability of thearea (Contreras and Solseng, 2006).

Figure 9 shows the pore-water pres-sure and total-head profiles at the site,illustrating the upward-flow conditions.Two vibrating-wire piezometer tipswere installed in the Huot Formationand one in the Red Lake Falls Forma-tion. The Huot Formation is fairly uni-form and has a permeability in the rangeof 1.2x10-8 to 1.9x10-8 cm/s. The ce-ment-bentonite grout mix used in thenested installation had a 2.66:1:0.27water:cement:bentonite ratio with apermeability of approximately 2.0x10-6cm/s. This example presents the resultsof the fully-grouted method in alow-permeability unit.

Example 3. Downward-FlowConditionsFinally, this field example demonstratesthe use of nested piezometers with theful ly-grouted method in down-ward-flow conditions. A total of fourpiezometer tips were installed in threeunits, with permeability ranging from1.0x10-3 cm/s to 9.49x10-7 cm/s. Wherethere is a wide range of permeability,the least permeable unit controls the ce-ment-bentonite grout permeability. Asa general rule, the less permeable the ce-ment-bentonite grout, the better, and asshown by the computer model, for mostsoil, a cement-bentonite grout with apermeability of 1.0x10-6 cm/s will beadequate. Figure 10 shows the pore-wa-ter pressure and total-head profiles atthe site, illustrating the downward-flowconditions. This example presents theresults of an installation of nestedpiezometers with up to four piezometertips in a single borehole.

Summary and ConclusionsThis two-part article presents a detaileddiscussion of the fully-grouted methodfor piezometer installation, including theprocedure and theoretical background. Italso discusses the results of a laboratorytesting program on six cement-bentonitegrout mixes, along with an evaluation ofa computer model to determine the im-pact of the difference in permeabilities

between the cement-bentonite groutbackfill and the surrounding ground.The following summarizes the articlesmain issues and findings: The practice of installing diaphragm

piezometers in a sand pack with anoverlying seal of bentonite chips orpellets could be discontinued.

The fully-grouted method is a fairlysimple, economical, and accurateprocedure that can be used to mea-sure pore-water pressures in soilsand fractured rock. It allows easy in-stallation of a nested piezometerconfiguration, resulting in drillingcost savings. It can also be used incombination with other instrumenta-tion (e.g., inclinometers) to measuredeformation and pore-water pres-sures, provided the inclinometerjoints remain sealed.

The permeability of the cement-ben-tonite grout mix can be up to threeorders of magnitude greater than thepermeability of the surroundingground without a significant error inthe pore-water pressure measure-ment. This finding differs from pre-vious assessments.

Laboratory test results show that thepermeability of the cement-benton-ite grout mixes is a function of thewater:cement ratio. As the water:ce-ment ratio (void ratio) decreases, thepermeability decreases.

Bentonite has little influence on thepermeability of the mix, but ratherappears to stabilize the mix, keepingthe cement in suspension and reduc-ing the amount of bleed water.

AcknowledgmentsThe support provided by the InnovationCommittee of Barr Engineering Com-pany is gratefully acknowledged. Thecareful performance of the laboratorytesting by Soil Engineering Testing ofBloomington, Minnesota, is greatly ap-preciated. The continual assistancefrom Erik Mikkelsen and his thoughtfulinsight and contributions from the be-ginning of the research program havebeen extremely helpful in pursuing theresearch and use of the fully-groutedmethod. John Dunnicliffs thorough re-view and comments on this manuscriptare also greatly appreciated.



Figure 7. Void ratio versus permeability.

ReferencesContreras, I.A., Grosser, A.T., and

VerStrate, R.H. 2007. BasicStrength and Deformation Proper-ties of Cement-Bentonite GroutMixes for Instrumentation Installa-tion. Proceedings of the 55th An-nual Geotechnical EngineeringConference University of Minne-sota. pp. 121-126.

Contreras, I.A., Grosser, A.T., andVerStrate, R.H. 2007. The Use ofthe Fully-grouted Method forPiezometer Installation. Proceed-ings of the Seventh InternationalSymposium on Field Measurementsin Geomechanics. FMGM, 2007.Boston, MA. ASCE GeotechnicalSpecial Publication 175.

Contreras, I.A. and Solseng, P.B. 2006.Slope Instabilities in Lake AgassizClays. Proceedings of the 54th An-nual Geotechnical Engineering Con-ference. University of Minnesota.pp. 79-93.

Dunnicliff, J. 1993. Geotechnical In-strumentation for Measuring Field

Performance.J. Wiley, NewYork, 577 pp.

Hvorslev, M.J.1951. TimeLag and SoilPermeabilityin Groundwa-ter Observa-tions. BulletinNo. 36,U.S. Water-ways Experi-ment Station, Vicksburg, MI.

McKenna, Gordon T. 1995.Grouted-in Instal la t ion ofPiezometers in Boreholes. Cana-dian Geotechnical, Journal 32, pp.355-363.

Mikkelsen, P.E. and Green, E.G. 2003.Piezometers in Fully Grouted Bore-holes. International Symposium onGeomechanics. Oslo, Norway. Sep-tember 2003.

Mikkelsen, P. Erik. 2002. Ce-ment-Bentonite Grout Backfill for

Borehole Instruments .Geotechnical News. December2002.

Vaughan, P.R. 1969. A Note on SealingPiezometers in Boreholes .Geotechnique, Vol. 19, No. 3,pp. 405-413.

Ivn A. Contreras, Aaron T. Grosser,Richard H. Ver Strate, Barr Engineer-ing Co., 4700 W. 77th Street, Minneapo-lis , MN 55435, 952-832-2600,[email protected], [email protected], [email protected]



Figure 9. Field example of fully-grouted method in upwardflow condition.

Figure 10. Field example of fully-grouted method indownward flow condition.

Figure 8. Comparison between a nested fully-groutedinstallation and individual separate installations.

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Use of Fully Grouted Method Barr Engineering