~ ~ ~

Enhancing the pe~iorI IIanceof large diarIIeter pilesby groutingby D.A. BRUCE>, BSc, PhD, CEng, MICE, MIWES, MASCE, MHKIE, FGS

IntroductionQUERULOUS EYEBROWS were raised in the1975 Offshore Technology Conference in

Dallas, Texas, when Gouvenot and Gabaixpresented the conclusions of their testprogramme on the effects of postgrouting onlarge diameter pile performance:—an increase in ultimate load of up to three

times in sands and clays,—similar increases in creep load,—highly repeatable performance under

cyclic loading with almost no permanentset, and

—direct relationship between ultimate loadand volume of cement grout injected.Since then, grouting techniques have been

employed confidently throughout the world,as a routine construction process. Byexploiting the higher values of skin frictionand end-bearing resulting, engineers havebeen able to reduce pile dimensions safely.There are thus relative savings in plant andlabour costs, as well as reductions in materialrequirements —a key logistical factorespecially in developing countries.

Equally, where the satisfactoryperformance of conventional piling has beenthreatened, either due to faulty orinappropriate installation techniques (e.g.Logic, 1984), or due to interference by laterconstruction activities (e.g. Karol, 1983),grouting as a remedial process has gainedwidespread application.

This review is a synthesis of data publishedprimarily in the last decade on pile grouting.Case histories are presented in three basiccategories:(l) Enhancement by devices placed within

the pile (i.e. attached to thereinforcement prior to installation).

(ii) Enhancement by toe/ground grouting(i.e. after concreting), and

(iii) Enhancement by ground consolidation(either before or after construction).

Throughout, the term "grouted pile" refersto a pile which has been treated in one ofthese categories. It is not used in distinctionto the term "concrete pile" for example.

Enhancement by devicesplaced within the pile

Such devices have been developed toimprove both shaft friction and end-bearing.The use for the former has been encouragedby the success of such as Osterm eyer (1 974)and Jones Ef Turner (1980) with respect toalbeit smaller diameter anchorage and

minipile systems. On the other hand, theneed to improve end-bearing performance,primarilyto minimisethe settlement requiredto fully mobilise it, has triggered intensivepractical research.

Bearing in mind that shaft friction is fullymobilised at displacements of 0.5-1.00/o D,but that end-bearing is maximised only atdisplacements of 10-15%D, it is clear thatthe service settlement criteria will usuallygovern the design basis, and that thefrictional component is likely to be fullymobilised.

Indeed, Lizzi (1981) noted that there iseven a tendency to over-design pile lengthsto thereby ensure adequate capacity in shaftfriction alone, reflecting fears thatdisturbance of the pile toe zone by pressurerelief or by upf low of ground water duringconstruction may seriously reduce the end-

10 200 I

10

O 15-c

erR i(

301

Section AA

Plan at pile base

Fig. 1 (rl'ghtJ."Preloading cell"grouting device,Parana RiverIBolognesi e Moretto

1 973)

Fig. 2 (top, rl'ghtj.Estimated settlementof hotel tower as afunction ofpile toedepth, CalrO (Piccione

eral, 1984)

Hook64msquare IIsteelplates

Groutho I es

spacers

1

TABLE I: TYPICAL BASE GROUTING VOLUMES(Bolognesi B Maretto, 1973)

Typical grout takesAverage Grout take

dPile diameter, number kg of portlanm of stages cement

1.00 (SS.RC) 2 5001.20 (SS.RC) 3 7001.80 (RCS.RC.LG)" 3 35002.00 (WS.BA) 5 60002.00 (SS.BA) Still experimentalSS: Steel Shell.RCS: Reinforced concrete shell.WS: Without Shell.RC: Reverse circulation.BA; Bucket augaring with drilling mud.LG: Lateral grouting to increase skin friction

of pile shaft.

Piles in the nver course

a0I

Depth: m

60 60

~Pilef'5< reinforcement

~ g

Plug

Neoprene sleeve100mm dia.

Smm dia.perforationson inside of tube

Grouting tube50mm dia.

dia. groutpipe

Lt-30mm dia. corepile reinforcement

25mm dia,

Rubber orneoprenesheet

>Contracts Director, GKN Colcrete, Wetherby, West Yorks.

'This is the first section of a two-part article. The second,to be published in our next issue, will cover enhancementby toe/ground contact grouting, enhancement by groundtreatment, summary and conclusions as well as all thereferences.

Fig. 3 (centre, right).Details of basegrouting device,Thailand

Uniformsl zegravel

Basket

14mm dia.

May 1986 9

bearing potential.Such disturbance to the underbase

material is almost impossible to eliminatecompletely. However, the effects may rangefrom not being of "practical importance" insoft rocks or clays (Sliwinski Ef Philpot,1980), to the other extreme: Sliwinski EfFleming (1984) concluded that "if a pile isfounded in cohesionless soils which are likelyto be disturbed, with a loss of the originalcompaction, consideration should be givento reducing or ignoring the end-bearing,unless pressure grouting is used to restoreit."

In addition to problems caused by baseinstability, end-bearing can be furthercompromised by accumulations of sedimentpreventing the "clean butt joint" of concreteand bearing material referred to by SliwinskiEf Philpot (1980), and by poor concretingprocedures. Endo (1977) notes that suchaccumulations may be up to 400mm thick atthe pile centre, and twice that at theperimeter.

According to Sliwinski Ef Fleming (1984)pregrouting of pile bases via grouting cellswas first reported in 1961 at the MaracaiboBridge site, whilst the similar system laterused for bridge foundations on the ParanaRiver has been described in detail byBolognesi Ef Moretto (1973). This projectinvolved several hundred piles up to 75mlong and 2m in diameter, each of which was"preloaded" through a basal-cell (Fig. 1).Each pressure cell had 40 holes, protected bya rubber membrane with an equal number ofoffset holes, thereby acting as a one-wayinjection valve. One grout line from thesurface extended to each quadrant of thecell. Suspended below, and fixed to the pilereinforcement, was a basket of coarse gravelsewing as a "grout and pressure distributionchamber". A neat grout mix of w/c ratio 0.66(by weight) was used in several phases ofinjection typically 12 hours apart. The targetvolume for each phase was 500-1 500kg,depending on pile diameter, and groutingwas repeated until either the target pressureof 100 bars was held for 5 minutes or a pileuplift of 20mm was recorded. Table I

summarises the typical grout takes. Theauthors noted that the technique not onlyimproved the characteristics of the soilbelow the toe, but it also served to appraisethe development of skin friction along theshaft.

More recently, Piccione et al (1984)

Fig. 4 fright/. The"preload" cell(Lizzi, 1981)

Beforeconcreting

Afterconcreting

After injectionof the

preloed bulb

~Borehole

~Reinforcement

~Injection pi pes

Double skinnedimpermeeble cover

Holes

Injection pipes

.3 w=. "'.w..3E.Perforeted ~ +~J ~ e (

pletes

MAINTAINED LOAD TESTPILE No.1 DIA. 600mm DEPTH 42m BUCKET EXCAV.PILE No.2 " 1000 " 42PILE No.3 " 1000 " 42PILE No.4 " 1000 " 43 5 BENTONITE CIRCPILE No.5 " 1000 " 43PILE Nos " 1000 " 46m BUCKET EXCAV.

WITH GROUTED TOE

SOIL DATA

GL LOOSE SAND~;~, & SILT

NORMALLY

E 20. CONSOLIDATEDSILTY CLAY=—:CLAY & SAND LAYERS

O 40. s>;~,.'EDIUMai~ DENSE SAND

EE 50-Z0I-O(uu. 100-O

150-

LOAD(kN)

5000 10 000

Fig. 5. ReSultS Of eXperimental pile teStS, Italy (Sliwinski 9 Fleming, 1984)

15 000

0IZ

described a similar application at the ElGazira Sheraton Hotel in Cairo. 76 piles1 800mm dia. for the critical lower structurewere cast into very dense fluviatile sands(N h 50). Individual working loads of 850tonnes were required for the 27m long piles,cased to 10m and drilled with bentonite flushtherebelow. Fig. 2 compares the total(calculated) settlement with and without thecell. (The calculated ultimate end-bearingresistance was 1 710 tonnes (BerezantzeVSformula)) and side friction was 226 tonnes(Kerisel's formula). Given the shorter pilelength and different soil conditions from thePara na contract, maximum g routingpressures were limited to 12 bars, in theorysufficient to fully mobilise the shaft friction.Typically grout takes were 500-1 500kg,with the lower value yielding the volumenecessary to fill the gravel pack voids.

Individual cell injections took between 2and 5 hours to complete. All piles provedcompletely satisfactory in service.

Most recently, the engineers of a major

10 Ground Engineering

Fig. 6 (rightj. Details and results fromCementation experimental grouting cell(Sliwinski & Fleming, 1984)

1. U-tube fabrication from32 mm dia. pipe

2. 8 mm dia. perforations3. Rubber sleeves4. 8 mm thick plate 405 mm dia.

in 457 mm dia. cased hole

I

.)

l

U-shapad grouting cell in position atbottom of hole

p0EE+c

A'5

—10

—15

—20

Load, kN500 I 000

50 mm

toe pilaeee

)()lade groundash fillbricks andclay fill

:= Boulder clay:=- and silty clay

Clayey silt'5 Black sand

is Silty sand N = 22

Founding level

Borehole strata

Load, kN

0 2 000 4 000 6 000 8 000 10 000 12 000ps

Soil condi tions

1//F;II

:== Firm clay

—10::.:".:Silt and sand30—';.'.':;SPT —15

Sandmedium

2p.;. dense40—.

" fine to,; . medium

:.;-.'PT5025. '..FL25

~ '

'SANO

REINFORCING BAR GROUTING PIPESSKIN

UTI NG

GROUT PIPETO THE BASE

EE Sp

c

+

as 60

~ Grouted base and skirt—Conventional (bentonite flush)

IN

GROUT PIPE,TO 1HE BASE

REI NFORCI NG

CAGE

Fig. 7 (abovej. Comparative perlbrmance of two 1 500mm diameterbored piles, on the same site, one grouted, one conventional(Sliwinski & Fleming, 1984)

Fig. 8 (rightj. Arrangement for toe and shaft grouting (stocker, 1983)

Fig. 9 (below, rightj. performance of bored piles of 570mm diameterwith and without postgrouting in sand with medium to high relativedenSity (Stocker, 1983)

GROUTSAREAS

ASE

TOP PLATEFIXEO TOTHE CAGE

t BOTTOSS THINPLATE

GROUTI NG CELL

cable-stayed bridge in Thailand havereverted to a system similar to that of Fig. 1

but without the suspended cage, (Fig. 3).Here 172 bored piles of 2 000mm dia. Up to35m long are being installed under the piersfor the bridge, and are founded in verycompact fine to medium silty sand. Test pilesof smaller diameter have proved thatdisplacements of over 120mm are necessaryto mobilise adequate end-bearingresistance, as a consequence of thehydrogeological and constructionalcircumstances. (No shaft friction isconsidered through the overlying soft clays).Grouting of the pile toes has therefore beenspecified to improve service performance.

0EE

10

cE'0a

Ul

Load, kN

5X 1000 1500 20X 2500 XX 3500

raulrs)

e base-alonq

he stall

Grouting is conducted in three separatestages (to 20, 40 and 60 bars, verified bygrouting trials), and in such a way as to avoidhydrofracture of the ground and so damageto that or adjacent piles. Injections are madewhen the pile concrete is "relatively weak",(i.e. less than 2 days). Strict controls havebeen placed on the timing (more than onestage) and the spacing () 4D) of adjacenttreatments, whilst the maximum pile uplift islimited to Smm.

Similar devices have also been developedby Lizzi (1981) (Fig. 4), whilst Sliwinski EtFleming (1984) cite test data from"experienced specialist contractors in Italy"(Fig. 5) and from their own company's

May 1986 11

Em

t00c0

300LL

200

100

mm

0

I

settlement = 10 mm

VovxoB

XXXX (

XXX

XX

XXX

000

~ AB()t)

4.

os

x ((gxX XX

1000- I 670 — 570—16001 900 900

o red p tes P os t - 9rou tedBore d P iles

Small- DiameterPi(e s Anchors

200- 1100- 120- 160-300 I 200 170 I 120

600

E400-z

- 3000V

200

set ttement = )Q mm

00

x x

~ OOOO00

OOOO~0000oo @

1000-1 600- 1300 1700-180011000

I900

R3st-groutedBored- Pr(es

200- I 100- 90-300 I 200 180

Std(-Diameter Arrhors wrhout

Piles est-grctiting

Oo0

(XOO(t(0

90—180

Anchas withFbs)- groating

600

EK 300

o 200

LJL

t)0C

Vt

~ OISIII p4

4

1000- 570-1500 900

Bored - Piles

570-900

Post - groutedBored Piles

settlement = 20mmov0

Y

4

Fig. 10 (above, leftj. Skin friction ofcastin-situbored piles (at a settlement of 10mmj andanChOrSin nOn-COheSiVe SOilS (Stocker,1983)Fig. 11 (leftj. Skin friction of castin-situ boredpiles with and without post-grouting at asettlement of 20mm in non-cohesive soils(Stocker, 1983)Fig. 12 (top, rightj. Skin friction of castin-situbored piles (at a settlement of 10mmj andanchorsin cohesive soils (stocker. 1983)Fig. 13(rightj. Skin friction ofcast-in-situ boredpiles with and without post-grouting at asettlement of 20mm in cohesive soils(Stocker, 1983)Fig. 14 (below, leftj. Base pressure of boredpiles with and without post-groutingin non-cohesive soil at settlements of 10, 20 and30mm (Soil type: 1-sand, medium density, 2= sand, high density, 3 =gravel, medium tohigh density) (stocker, 1983)Fig. 15 (below, ri ghtj. Base pressure of boredpiles with and without post-grouting incohesive soils at settlements of 10, 20 and30mm (Stocker, 1983)

300EK

200

lJ

100C

s/1 0

Dd0~0D

Sto

1300-1

600-1800 I 1000

Bored Piles

700-1300

Post - groutedBored Piles

settlement = 20 mm

setllemeht =10mm. settlement = 20mm settlement=30 mm

3000— settlement = 10mm settlement =20 mm settlement o30mm

3000—

-2000(-

Q.1000

0o3

I)o

~ +

~ 000

0~ 0

+ ~ 0

IkVF(e 12 3 2 3 1 2 3 2 3 12 3 2

Boed Rl 9 tro ed PkL0 Bor d P )esBooed P I

" 'o d~R)es 'orecr R(as

~E

z~2 000

0

u1000—Q

i(XO+ OX+

tr+Q ~

Bx QP(~

XX

+xxxx

+OO+

Poet -Brouiad ~ p ()00'.-9rc(uted ~~ pkPoet.-groukd

Bored P)es (Bored P(l(ts Borerd P()rts

experimentation "some years ago" (Fig. 6).The same authors also quoted results from "acompany working in the Middle East" (Fig. 7)featuring systems designed to incorporateimprovement in shaft friction as well.However, on this particular topic, the mostcomprehensive and quantitative contributionappears to have been made by Stocker(1 983).

He described the tube 8 manchette/flatjack combination of Fig. 8, andrecommended that to improve shaft friction,injection after 1 or 2 days, at pressures up to50 bars, be conducted, repeatedly ifnecessary. For improvement in end-bearing,grouting at the same interval to 60 bars wasexecuted. He emphasised that the head dis-placement during toe grouting operationsmust be carefully monitored and limited to

3mm: higher displacements could decreasethe frictional resistance subsequentlymobilised. He also reminded that the amountby which the bearing capacity can beincreased depends on the type of soil and itsvirgin density. Typical data are shown in Fig.9, whilst the results of Stocker'sexperimental data may be summarised asfollows:

Effect on shaft frictionNon cohesive soil

Figs. 10 and 11 show results atsettlements of 10 and 20mm respectively.(The elastic deformations were notconsidered). These results show increasingfriction with decreasing diameter, ascribedto the effects of dilation and constructionmethod. Stocker did emphasise, however,

that the post-grouting of the large diameterpiles was by high pressure at different levels,whilst minipiles and anchors were grouted atlow pressure (5-6 bars) over their wholelength, during installation.Cohesive soils

Figs. 12 and 13 show results atsettlements of 10 and 20mm respectively. Adistinct relation between diameter andfrictional resistance is apparent, with a majorimprovement made by post grouting(supported by data of Ostermeyer (1974)and Whitaker Et Cooke (1966)).

Effect on end-bearingNon cohesive soil

Fig. 14. Although theoretical studies(Meissner, 1982) have shown a clearrelationship between end-bearing capacity

12 Ground Engineering

00

Load, kN Fig. 16 (eft). Pile load test results, Pile Test 1,

SOO 1 OOO 1 SOO 2 OOO 2 SOO 3 OOO 3 SOO 4 OOO 4 SOO S OOO S SOO 6OOO Pier E-55, Jeddah issuer AG)I I I I I

2.0-

4.0-

6.0

8.0-

c 100-

<yi 12.0Pile diameterPile lengthGrouted lengthWorking loadTest loadSettlement under working loadSettlement under test loadPermanent settlement

I

770mm22.5m3.5m2 500 I<N

5 OOO kN3 51mm10 01mm2.47mm

I I

and pile diameter, this was not conclusivelyconfirmed by Stocker's tests. A "veryessential" increase of the base pressure was,however, attainable.Cohesive soil

Fig. 15.These data are for piles from 620to 1 800mm in diameter. From limitedresults it would appear that post-groutingincreases the bearing capacity significantly(but less than in non cohesive soils) withinthe range of working loads considered.

To illustrate the practical application of themethod, Stocker's company have reportedon a project executed in Jeddah between1981 and 1983 wherein 1 072 piles of770mm dia. (working load 250tonnes) and1 213 of 900mm dia. (working load375tonnes) were installed. These piles

sxecs

Geologicaldescnption

Classificanon 5

Fine sand~ Sand and ~~ silly layers~

Fine sand

Static penetrometer

Point resistance Ckp (bars)

10 20 50 100 200 500

Dynamic penetrometer

Point resistance Rp (bars) u5 10 20 50 100 200 500

Menard pressuremeter

Limit pressure pt (bars)

5 10 15 20

10 ~ Silt

Fine sand

Silt

20Fine sand

ss

c00'

PR1

Silt

Medium sand30

~coarse ~sand

Ypresclay

—SP1 ———-SR2

—DP.1 ————DP. 2

40—GOUDA penetrometer

Capacity . 10 tonnesConical pointCross section 10 cmsCone angle

60'ERMES penetrometerBentonite in)ectionExpendable coneDiameter 70 mmCone angle

45'asing~

27in dia.

Grout

v—31 5m

E<o

Clay

E E

Depth, m

02.4.68.

10.12.1416.18.2022.24.2628.

Fine sand

Silt

Fine sand

S i It

Medium sand3032343638-40

-- ~- Coarse sand

Ypres clay

Fine sandSand and silty layers

Fine sand

Si It

)i)

E

1)e-31 .smil

. Clay

Fig. 17 (aboveJ. Summary ofsiteinvestigationdata, N. FranCe (Gouvenot & Gabaix, 1975)

support 300 piers carrying an elevatedsection of the Jeddah-Mecca Expressway.The soil consisted of loose silty sand andbroken coral (—5 to —28m) overlying hardcoral limestone. The piles ranged from 8 to30m in length. Grouting was executed at thebase, and along the shafts (in the densesand). Fig. 16 shows the excellent testloading results of a 22.5m long pile, 770mmin diameter, tested to twice working load (i.e.500tonnes).

Fig. 18 (ieftj. Location of test piles, N. France(Gouvenot a Gabaix, 1975)

May 1986 13

TABLE Ilt SUMMARY OF GROUTING OPERATIONS (Gouvanot e Gabaix, 1975)

Injection I, Injection l, Total

Pilenumber

A,A,AsB,BsBs

groutedsoil

SandClaySandClaySandClay

G routedlength

in

metres

1 2.507.809.507.40

1 3.407.40

Quantityinjected

in

tonnes

1 7.7

31.51 9.7

1 8.8

Mean groutpressure

at the endof grouting

in bars

25-30

12-3020-30

20-50

Quantityinjected

per metreof groutedlength in t

1.4

3.32.65

2.55

Quantityinjected

in

tonnes

32.126.457.65.4

25.611.25

Mean groutpressure

at the endof grouting

in bars

30-4020-5050-8050-801 5-3050-100

Quantityinjected

per metreof groutedlength in t

2.553.41.250.731.91.7

Quantityinjected

in

tonnes

49.826.4539.125.125.630.05

Quantityinjected

per metreof groutedlength in t

3.953.44.13.381.94.23

TABLE III: SUMMARY OF LOAD TEST RESULTS (Gouvanot a Gabaix, 1975)

EoPileNos. Q, Q,

200A, (ex) 120

Qt

Qr

1.6

E,

Qt Qr

350(ex) 220

Qt

Qr

1.6

E,

Qt

520(ex) 330

Qt

Qr

1.6

Compression

QtQt Qr

Qr

Pull-out

Qt Q,QtQr

A,

70 400 420As (r) 55 1.3 (ex) > 300 (ex) > 400

Poorly 260defined> 300

Poorlydefined > 300> 300

180 370 440B, (r) 120 1.5 (r) 240 1.5 (ex) 270 1.5

B,

G routingdestroyed byloads on 8,

450 300 1.5 160 140 1.14

180 440Bs (r) 120 1.5 (ex)

490290 1.5 (ex) > 400

ex —Load found by extrapolationr —Effective load without extrapolation

Qt —Ultimate bearing capacityQr —Creep load

All loads in tonnes

Injection point blocked bytop sleeve of packer

va inflated with waterks injection point

Inner tube of packerassambly 160 mm dia.

Pile 508 mm dia.

Fig. 19 (left/. Post grouting device for pipepiles, N. France IGouvanot & Gabaix, 1975)

cv- o

at%BI'RSZK'Mv ~~ Qmt

ssxssv. ~rm~=;-==--- -x==-~u

h msrout

Lower sleeveinflated with water

Injectionpoint open1 000 mm

In)acoon point blockedby lower sleeve

Log time, min

3 4 5 10 20 50 100I I I I 401

I )20

200

1 2Load on the pile cap, tonnas

0 200 4000 ~

EE, Q . Esi8

Es

S 30I (a)Z

0

67.8"9

101112 ~240

I280

I320t

2 3 4 5 10 20 50 100min

16

E 21E 22c~ 28

29m 30

(c)0 32

1

3(b)

00

Eto .~E

200 400t

The work of Gouvenot Er Gabaix (1975)concentrated solely on the improvement ofskin friction as a means of reducing offshorepile geometries. These tests followedGouvenot's (1973) experiments with soilanchors where a 2-5 times enhancement offrictional resistance was attained. A six pilefield test programme (Figs. 17 and 18) wasconducted in fine-medium silty sands andFlanders clay. Over the uncased pile lengths,subsequently pressure-g routed, thediameter was 660mm, formed by rotarydrilling with water and/or bentonite in thesands, and by auger and bucket in the clay.

Pile reinforcement consisted of a 508mmo.d. steel pipe of 11mm wall thickness, intowhich was attached an inner tube assemblyof 160mm i.d. (Fig. 19), permittingsubsequent pressure grouting at discrete 1mintervals, through non-return valves.

The initial phase of pile grouting (i.e. atgravity pressure, while installing) wasreferred to as lo, whilst later pressure grout-ing operations were referenced l, and I,.After each of these three phases, load testingwas conducted (i.e. E,, E, and E, data).Grouting results are summarised in Table II.

Fig. 20 (leftJ. Performance of Test Pile A 1 insand, N. France (Gouvanot & Gabaix, 1975)

14 Ground Engineering

The substantial improvements in

performance after each of the phases ofpressure grouting are shown clearly in Figs.20 (sand) and 21 (clay), whilst the results ofthe whole programme are summarised in

Table III. As indicated in the introduction tothis review, the authors were able to makeseveral clear and important conclusions,principally:(1) Q,, the ultimate bearing capacity, is very

sensitive to the effects of grouting —by afactor of 2 to 3.

(2) Q„, the creep load, varies similarly, withthe Q,:Qr ratio (1.3to 1.6) independentof the grouting influence.

(3) The piles remained very stable undercyclic loading: after several cycles nopermanent displacement remained.

(4) The increase in Q, is directly proportionalto

(V+ V)(V.+ V,)

for both clay and sand (Fig. 22) assumingcontrolled pressure and volume (i.e. noclaquage),where V = volume of grout injected

Vp = volume of pileV,= volume of grout used for

initial gravity grouting.

(to be concludedj

Load on pile cap, tonnes

200 400 6000

ja,

I

I40.I

Ec(I

E0E

1

2'

60

a6e'a

+

eZc

v- 0O sc

COfh

0 .=to 4

IA

80

X Et

(a)

1004

Ee ~ Et

0 200 400 600

Fig. 2 1.Performance of Test Pile B1in clay, N.France (Gouvenot a Gabaix, 1975)

05c)

a4

E,AE2A2 (sand

Theoretical

I

I I

EtB2(clay)e +

E2Bl (clay)

El B1

(clay)

Et A t (sand)

0 1 2 3 4 5 6

V = Pile volumeP

V = Volume injected under pressureIl = Volume filled without pressure

Fig. 22. Inferred relationship between groutvolumes and enhancement of pilepafformal)CB (Gouvenot 8 Gabaix, 1975)

Q< = Ultimate bearing capacity of the pile

Q = Effective grouted diametersA = Coefficient characteristic of the pile's geometry

(grouted length)

QLlQLo =

Ultimate bearing capacity after pressure grouting

Bearing capacity before grouting

FACING THE FUTUREWITH 100 YEARS QF EXPERIENCE.

SJg

CK'M',LIUS COMPANY LTD.Head Office and Works: Long March, Daventry, Northants NN11 4DX

Telephone: Daventry 703431 (STD Code 0327) Telex: 31600

May 1986 15