ratoryandproced~~.

g dance ont~ety for Rock M

" ie htternatioes is given b

e advice on mteg des provide

Practice are ltafion and m

arly withrwed rigorousi

me~em~~tothe

y

"o 'ntal strainve tical andmentofr i

shear streween iaborat

is much less st

'c field values

doctm,e tedy Performed or

to mterpret; coror imposslb

geotechni~gently many

confidegineers have httl

"cein rock ahrely mstead on e

ar st data and

review and" "Perience, item~

or empir.~' e

ofBaIton (igZ s . ds such

rise to Id'proach

erableel 0

shearst e ~ rrockdlscobe extremely

naiover a much

shear strength vg eater range th

Thhvalues of sou,

PaPer describefofiowing ~ and discusse

ete sta. s e

o whichis 'tmg,eachfgesofdirectsh

d accurate mtunpoItant for Mi

~~ terpretation of re ul

phng

ts.

~entation~ Testing~~y is~ Lterpretation

Fundament~stren@h

fshear

s there are si leant differ

Plane ofwe~g neral term for

exess inrock f

Ple, a jomt bedol'leavage

or sch . g Plane,

~ Th ~em~um al

g histheue ofsheaear stress in the

Laboratory ~testm

~ ect shear

%afro'iscontinuities

by SRy SRHenchert &LR RichardsO

tiFeis- ilyteee ~s. - - ss - ~'-

i s ~ eesM ice MMasstu~S' ~ e:~ i ~

- ss - ~Iilai'Nr ~ e:~ i ~

- See S i.l ee.is tete) ~ I iirlrr i see

Introduction

The asseassessment of thekdis o

damentaltion of fun

's

quantification of the infi a orsarameters t e

uence off ctoo g

s'nceand'nf ill for theuity in situ.

The aim of this paper is

ength of rockuiti . se

thepecifically with dir e

laboratory. A furt

'ct sheher paper is

o consider fle'esandinsitush

eld evaluation f

e testing method dise orrockthatis

'ussed here'

hdao 'ion effects to bepplied normalt under the a

uiti ouor continui u'c ess ofweak infill.

Basic frictional paramd 'ed by direct

BASIC FRICTION

~ NON Dl LATING SURFACE

~ IPO DEPENDS ON

TEXTURE

RANGING FRAND MINE

FROM Ir'ORIFICIALLY SMOOTH

SURFACES

EO

TO MOe

INTERLOCKING

~ OIERRIOING OR SHEAR

SURFACE LR AISTIES

ADDITIONAL

ENGTH TO BASIC FRICTION

~ TESTS ON SAMPLES OF

DIFFERENT ROUGHNESS

NSIOERABLE

R IN PEAKMEASURED

X

T.

X

X P'~'i

COHESION

~ SHEARING OF INTACI ROCK

5 OR HEALEDIONG OF KSNT

PROVIDE ADO ITIONAL SIRENGTH

OF SITACT MAT

RTIONAL TO THEMATERIAL SHEARED

sc

COHESION

shear testmg in the

24t Department of Earth Scie0 Gold

, University of Leeds

GROOUND ENGINEE RING . MARCH .. 1989

KET

= SHHEAR STRESS

Q = NORMAL STRESS

Fig.l. Factors tribacontribatin

X = PEAK STRENGTHS

triba g to shear. strength.

shear stress versus shear displacementcurve for a given normal stress value.

~ The residual shear strength is thestress at which no further rise or fall inshear strength is observed withincreasing shear displacement.

~ The basic friction angle represents thefrictional component of shear strengthonly. Basic friction will vary with thesurface texture and mineralogy of thediscontinuity surfaces. The basicfriction angle is not necessarily equal tothe residual angle of friction of a roughdiscontinuity.

~ Cohesion is the shear strength at zeronormal load. Rock discontinuities oftenhave no true cohesion. True cohesionwill occur where rock bridges arepresent across the discontinuity orwhere secondary mineralisation hascaused chemical bonding.

~ Apparent cohesion is the value of theintercept on the shear strength axisformed by the tangent to the shearstrength envelope at a given level ofnormal stress.

~Multistage testing involves testing thesame discontinuity sample at differentnormal loads. This is often donebecause of difficulties in obtaining asufficient number of reasonablyidentical samples and the need toobtain maximum information from eachsample.

The factors affecting the shear strength ofrock discontinuities are generally wellunderstood (at least in qualitative terms).Fig. 1 shows the main concepts and theseare further summarised below:

~ A persistent, smooth and planardiscontinuity (non-dilating) will show apurely frictional resistance proportionalto normal stress and this will depend onthe surface texture and mineralogy ofthe discontinuity.

~ Real joints are almost invariably non

!planar and additional strength duringshearing will be obtained from the needto overcome interlocking by over-riding and/or shearing of asperities.

~ A true cohesion (or area dependentstrength) may result from lack ofcontinuity across rock bridges andsometimes due to secondary mineralinfill forming chemical bonds across thesurfaces.

usswt w incmc ~ r I

IWNCIIW 5 &I'llLI ~ I I

QL:'.....iI::..:—....::v4-....'-,>:~

Fig.2.General layout of Golder shearbox.

The basic friction angle of adiscontinuity is independent of the sizeof the surface being tested. Thisparameter can therefore be readily andaccurately determined by laboratorytesting on small samples. However,cohesion (whether true or apparent) isstrongly dependent on the area of thesample being tested and determinationof this parameter requires carefulconsideration ofboth laboratory andfield size effects.

In order to assess the in situ shearstrength of a rock discontinuity, eachcontributing factor must be determinedseparately and then combined toproduce the overall shear resistance.Laboratory testing is used for thefollowing purposes in this process:

~ Definition ofbasic friction angle.

~ IdentiTication of surface characteristicsthat control shear strength in theapplicable normal stress range.

~ Observation of performance andcontribution to strength made by minorasperities during shear, ie whether theyare sheared through or over-ridden atparticular stress levels.

The contributions to shear strength madeby in situ roughness and impersistencecan be assessed only by careful fieldstudy and references should be made toother papers for information on this topic(eg Cowland &Richards, 1982).

Direct shear test apparatusThe general requirements for direct sheartest apparatus are clearly set out in therelevant ISRM suggested method (Brown,1981).'hese requirements may beachieved with minor modiTications toconventional soils shear machines.However, testing. with these machinesoften involves considerable difficulty with

mounting rock discontinuity samples andmaintaining the necessary clearancesaround the sample and between the upperand lower halves of the box duringshearing. The load capacity of soilsmachines may also be inadequate for rocktesting.

The most commonly used apparatus forrock shear testing in thyUK is the'portable'hear box developed atImperial College and described by Ross-Brown and Walton (1975) and Hock(1981). This machine is also the only onereadily available in the country. Theapparatus can yield reasonable resultswith experienced operators but has anumber ofdisadvantages. The principaldifficulties relate to the method ofapplication of the normal load. It is appliedby means of a hydraulic jack on the upperbox and acts against a cable loop attachedto the lower box. Because of the cableloading system, any tendency towardsdilation on rough surfaces leads to anincrease in normal load and thereforeadjustment of the normal load jack isrequired throughout the test. Withincreased shear displacement, theapplied 'normal'oad moves away fromthe vertical and corrections for this maybe required. The constraints on horizontaland vertical movement during shearingare such that displacements need to bemeasured at a relatively large number oflocations if accurate shear and normaldisplacements are to be obtained. Oneother drawback is that the shear box isdesigned for testing over a range ofnormal stresses from zero to 154 MPa andis rather insensitive and difficult to use atthe relatively low stresses associated withmost civil engineering works.

A more suitable direct shear testapparatus is that developed by GolderAssociates'ancouver office in the early1970s.A number of these devices havebeen fabricated and are in use in the UK,Canada, US, Hong Kong and SouthernAfrica. The apparatus has been brieflydescribed in Hencher and Richards(1982)'ith the general layout of themachine being as shown on Fig.2.Theapparatus has been kept as simple aspossible yet is adequately sensitive formost testing situations. There are severalinherent advantages in the design, namelythe rapid set up and testing time, small sizeand simple constant normal load system.The normal load is applied by means of adead load system and therefore remainsconstant throughout the test. For the

GROUND ENGINEERING MARCH . 1989

25

1. SAMPLE DETAILSi SAMPLE OESCRIPTION SHE ET

POST SUOINGI

SAMPLE ILLUSTRATION SHEET

XYS'ifC,~ NO,5

IP H4y, dcylh o-yH8o~~, uiDo.S~Aoo

1~~ (oculo-~

2. ROCK DESCRIPIION-HAND SPEQMEN

-iryrsm, f rts. '&aNIÃ6, oAsNrf+ ydlfI siysNri. Sgdj~IdoryffI Aofiscg coioNe.~ lseso ~ fzrs ruL. ~HrwroilI

IPsNUIT of oPsR Eorm s«ILIUII k» ~ a5P IIM'essaK

gtrRrt I Issr . Q'cssIHlsrIRS BN ~, IeINVIMR Uorsr'fs VhVNIVNUA «UHA

Syfikkk, «iud'o . Uirr Afirorgst Ltsotroj eI dsfA reek.

2.IKXIGHNESS

A

B

C

3.SLSIRrrCE DESCRIPTION

ANNOTATED DIAGRAMS

rgreogoB'~ otsliding

I ~ JA == »»'- -- --~ 'A'

1»

C J P ~~ cC

PHOTOGRAPHS

3.OsccNTNUITY DEscRPTKss

, IPSNsrI wP PyTer Trr 1geINHI p Pere@ Ieorj. fiji,

~Q M d4. Itu..

4. SAsPLE aMENSlae

BOTTOM ~~ BOTTOM

BIRECT SHEAR T EST S SAMPLE NUNER

XYZ SITEEngineering GeologyLEEDS UNIVERSITY

Fig.5.Example ofsample documentation sheet.

BIRECT SHEAR TE STS SAMPLE NUMBER

XYZ SITEEngineering GeologyLEEDS UNIVERSITY

Fig.6.Example ofsample illustration sheet.

Wherever possible, mating joint surfacesshould be selected for testing ifrepresentative of the in situ discontinuityalthough non mating surfaces will oftenyield similar basic friction values after thecorrections for roughness. Even allowingfor dilational effects, mating surfaces willsometimes give higher correctedstrengths. This is generally due to closetextural interlocking (non dilational) inmatched surfaces.

Samples must be cut to size to fit the shearbox and set in dental plaster or some othersuitable fixing medium. Kaffir D dentalplaster available from British Gypsum isused at Leeds University. The optimummix for this plaster is 100parts plaster to 35parts water (approximately 1.5kg plasterto 0.51itres water). The plaster sets rapidlyand achieves a compressive strength of23MPa after 2 hours and 40MPa after 12hours. The procedure for setting upsamples is illustrated in Fig.4.

Documentation

One of the weakest aspects of manytesting programmes is the standard ofdocumentation. Obviously, the derivationof samples should be recorded (ie, theborehole number and depth or fieldlocation). However, the nature of

28 individual samples before and afterGROUND ENGINEERING MARCH 1989

testing needs to he recorded togetherwith all pertinent details of the testprogramme itself. Typical proformae forsample descriptions are given in Figs. 5and 6.The descriptions need not be overdetailed but should he sufGcient to recordthose factors that will influence the testresults. The most important descriptionsare those relating to surface mineralogyand minor morphology.

After testing, the surfaces should beexamined, particularly with regard to theconditions of the areas involved inshearing. It is good practice tophotograph surfaces before and aftershearing using low angle lighting toemphasise the relief. The general

Fig.7.Use ofpro5le gauge to measuresurface roughness ofsample.

roughness of the surfaces can berecorded using a simple proGlograph asillustrated in Fig.7.These measurementsare taken for documentation purposesonly as the effective roughness must becalculated from dilation measurementsduring the test.

Test procedureFollowing initial sample set up anddescriptions, the shear box should beassembled and the first normal loadapplied. The normal stress range shouldbe selected to simulate the Geldconditions. If tests on wet surfaces arerequired, a dam ofmodelling clay can bebuilt around the lower hox and waterintroduced using a squeeze bottle.

Testing can be carried out by either singleor multistage procedures. For single stagetests, each sample is sheared at a constantnormal load. The aim is to obtain bothpeak strength and residual strengthvalues. The residual strength is not amaterial constant but is a function of theoriginal roughness (sample variable), thenormal stress level and ultimately thecondition of the final surface and debrispi'oduced.

In multistage tests, the normal load isincreased (or decreased) after peak

4

HG

200.

strength has been measured at eachstage. It is usually sufficient to shear for afurther lmm or so after peak to ensure thatshear strength is either falling orremaining constant. After each stage, thesamples may be reset to their originalposition. However, this is oftenunnecessary and shearing can continuefrom the same point after changing thenormal load if there is sufficient sheardisplacement still available to allow thenext stage ofpeak strength to bemobilised. To check whether damagecaused during earlier stages may affectresults at later stages, one or more testscan be carried out with increasing anddecreasing loads as shown in Fig.8.

It is good practice to carry out tests withdifferent normal loads for the first stagesso that first stage results can be used bythemselves to define a strength envelopeifnecessary. The major advantage ofmultistage testing is that more data areobtained from each sample. Often onlylimited numbers of suitable samples areavailable and the setting up of samplesand proper documentation are the mosttime-consuming parts of testing.

Rates ofshearing below a few mm perminute do not affect test results as a rule.

LEGEIG

FaLLING LOaO SERIES

"RISING LOAD SERIES

4L STaGE 1EST ON

NATURAL JOINTTHROUGH DOLOMITE

5OI. «NJME

00 5 10

HORIZONTAL OISPLACEHEHT (oml

44

aX

Very high rates of shearing (say ) Imm/s)may give different strengths (Schneider(1978); Hencher (1981) Gillette et al(1988)zz.

In order to be able to analyse resultsproperly, horizontal and verticaldisplacements must be recordedthroughout the test. The correctionmethod recommended here makes use ofincremental roughness angles which mustbe known at each shear stress data point.As all the test measurements must betaken at the same time, this can be difficultwhere data are recorded manually,particularly near peak strength wherechanges may occur very rapidly. It is oftennecessary to have two assistants andpractice is generally required beforereliable results are achieved. Data are

IM 'IEI 3M LM 5M

NORMAL 5/RESS. 0 lkN/mll

4

Natural joints through Dolomite,

Dokan, Iraqpeak strengths. Datauncorrected.

MH.

2

5$1.PL'H4

N4

K LEGEIS4K 0 UNCOATED JOHTS

X JOINTS COA1EO WITH

MTUNEN/CALCITE

SIH Im 1510 EMI

NORMAL STRESS, 0 lkH/mll

Fig.10.Peak strength data, uncorrected.

Test dataTests canied out as recommended in thepreceding sections should provide acomprehensive record of shear load andvertical and horizontal displacements.Normal load is usually kept constant foreach stage of testing.

Shear and normal loads are converted toaverage 'engineering'tresses bydividing by the gross contact area of thesamples (this will vary throughout thetest). The contact areas of ellipse shapedsamples (from rock core) at givenhorizontal displacements can becalculated using the following formula:

ln.

HNJ 2

E

r-0 M60:361

I

0: /OmsIZIH.

100.

0 TJL

CD= 266

00 5 10

HORIZONTAL OISPLACENENI (mml

LGG.

3M

8200

100.

HO

K

O

STRESS CORRECTEDFOR DILATION

LEGEHO

X PEAK STAEHG1H FOR FALLINGLCAO MJLTI-STATE

0 PEAK STRENGTN FOR RISINGLOAD MULTI. STAGE

00 HS 2M 300 100 500

NORMAL STRESS lkH/mll

Fig.8.Examples of results from risingaud falling load multi stage tests.

HORIZONIAL 015PLACEHENT lmml

Fig.9.Example of raw data.

typically recorded at set increments ofhorizontal displacement (say O. lmm).However, closer intervals may berequired where, for example, the samplesare dilating strongly with increasing shearstress yet horizontal displacement isessentially zero. The computer-basedretrieval system in use at the University ofLeeds allows data from all channels to beread at the same time and at very shorttime intervals (tenths of a second). Thesoftware allows the rate of retrieval to beincreased or decreased throughout thetest.

On completion of a test, samples shouldbe examined, the nature of the surfacedamage described and the surfacessketched and photographed.

where A = gross area of contact2a = length of ellipse2b = width of ellipseu = relative displacement

Block samples can often be approximatedas rectangular or other simplegeometrical shapes for the purposes ofcalculating stresses. The true contact areabetween samples is always much smallerthan that calculated and the local stressesare correspondingly higher. However, thestresses calculated on the basis of thegross or apparent contact area will be inaccordance with those calculated for thefield condition.

The raw data is best presented asFig. 9with separate graphs showing shearstress versus horizontal displacement andvertical displacement versus horizontaldisplacement. It should be noted thatwhilst only single values of normal stressare given for each stage in Fig. 9(corresponding to peak shear strength), 29

GROUND ENGINEERING MARCH . 1989

nm.m

LEGESO~ TCORRECKO DATA

I STRESSES CONNECTED

ITNNI OILATICR

the calculated normal stress does in factincreasethroughouteachrunduetodecreasing contact area.

Fig. 10shows results from two series oftests with peak shear stress plottedagainst normal stress. These showconsiderable scatter and it is found thatthe wider the range of roughness ofsamples tested, the greater will be thescatter of this plot. Interpretation of resultspresented in this way is extremelydifficult. An upper bound envelope, forexample, would merely represent thestrengths of the roughest samples testedand the basic friction angle of the materialcould not be determined.

Correction oftest data fordilationAs dilation occurs, work is done hi liftingthe upper sample and this results in anincreasing shear force being re~ed tocontinue shearing. Patton (1966),conducting shear tests using toothedplaster models of simple

geometry,'howed

that the contribution due todilation could be explained by thefollowing relationship:

r = 0 tan(8+ i)

where r is shear strength, o is normalstress, 8 is the basic friction of thesurfaces and i is the angle of inclination ofthe toothed asperities causing dilation.

REASURED RORRACSTRESS lmmmm I - 0

) dv

As shearing takes place, top block dilates with workbeing done against normal load through dv

To calculate stresses relative to actual plane of shearing

Then, i = A Tan~dv

5; = (r cosi —osini) cosio;= (ocosi+ rsini)cosi

Where compression takes placethen, r, = (r cosi+ osini) cosi

ll; = (ocosi —r sin i) cosi

Fig.Il.Resolution ofstresses relative to30 actual plane ofshearing.

GROUND ENGINEERING MARCH 1989

m EW lsnEONAL SISESS (ks/mrl

Fig.12.Stress path plots corrected anduncorrected for multi stage test (sametest as Fig.9).

The dilational contribution to shearstrength can, therefore, be simplyaccounted for by the geometry of thesample. Where shearing of majorasperities accompanies dilation, acohesion component ofshear strength willbe introduced but the contribution due tooverriding can stQ1 be calculated on thebasis of the geometrical path followedduring shearing. The relativecontributions to strength of basic frictionand cohesion can be determinedindependently once the extra work donedue to overriding has been accounted for.

In practice, the incremental roughnessangle can be calculated throughout thetest by considering the incrementalvertical (dv) and horizontal (dh)displacements as follows:

dv/dh = tan i

Stresses measured in the horizontal andvertical planes can then be resolvedtangentially and normally to the planealong which shearing is actually takingplace using the equations given in Fig. 11.These corrected stresses may then beplotted to give a strength envelopereflecting the shear strength of nondilating, naturally textured surfaces. Thisenvelope may indicate purely frictionalbehaviour (through the origin) or mayshow additional cohesion which might beexpected to vary for different samples andstress levels. In the experience of theauthors, the majority ofpersistent rockjoints exhibit essentially frictionalbehaviour once dilation has beenaccounted for.

In Fig. 12, shear stress is plotted againstnormal stress (graduaQy increasing due todecreasing surface area in the case ofuncorrected data) for four stages of adirect shear test. Both uncorrected dataand data corrected for dilation are plottedin this graph. A strength envelope can bederived directly from the corrected data.In Fig. 13,the ratio between shear stressand normal stress is plotted versushorizontaldisplacement for bothcorrected and uncorrected data from thesame test as in Fig. 12.The influence ofdifferent roughnesses and hence different

dilation angles is evident in theuncorrected plots for the four stages.

In Fig. 14, the peak shear strength resultsfrom Fig. 10are replotted with stressescorrected for dilation. The reduction inscatter is marked and the basic frictionangle is clearly defmed by the correcteddata points.

Influence ofsurface textureand, coating on resultsDiscontinuities from the same rock typeand of similar surface texture andmineralogy will generally yield a welldefined strength envelope oncecorrection has been made for the effectsof individual sample roughness. Frictionangles thus obtained will often be verydifferent from the basic friction anglemeasured either from tests on saw cutsurfaces of rock or from residual strengthtests. In tests on joints through Hong KongGranite (Fig. 13)the corrected valueobtained for naturaQy textured surfaceswas 6'igher than that obtained from testson saw cut surfaces of slightlydecomposed granite (Hencher &Richards, 1982)'.The corrected frictionangle for natural, uncoated joints throughdolomite was 10'igher than that obtainedfrom saw cut surfaces.

Surface coatings may result in correctedfriction angles considerably lower thanthose for clean discontinuities andsometimes lower than those for saw cutsurfaces. Dolomite coated with minoramounts ofbitumen and/or calcite wasfound to have a basic friction angle ofabout 33'ompared to 39'or uncoatedjoints. Tests camed out on joints frommonzonite in Hong Kong gave values of

Ettttf+~DATA

CINRECIEO DATA

1.0

5 uEOEIEOEIAL OISPLACEREEI Immi

Fig.13.Shear stress nomtal stress ratioversus horizontal displacement (sametest as Figs 9 and 12).

IE

E

(8NN

I NO.

I llg

0

ESNAL SN(SSS ACNNN SAmEl

EA(s O; (0(NO(i

N TOOITC COAEO WITH

0

ETIHEHICAICTE

4 SNI NE ENNINA( SNSSS, 0; (NN/ol)

Fig.14.Peak shear stzenFig.10corrected ffor dilation.

38'or iron oxide stained joints bwhere the rock had a thin

c cteristicstative in terms of surfac

and ofdescribing the

aces carefull ine

y in order that the resultsy intezpreted properly.

In summary, the frictional res'oresistance of anut naturally textured

'co tin ty ym that measuredy different from

hiaces. Values may be

LZL

'gher due to increased extural'erlocking or may be far lo

texturalar lower due to

assuming a basic fzicttc 'ction angle of, say, 30'ps on the basis of testin

cut surfaces) is liable toe to producecant ezrors.

Conclusions

The Geld shear strength of rockdiscontinuities is a difGcultdetermine, not least hecaproblems ininvesti tin

e use of thega g aztd quantifymg

ence and roughness of thefeatures. The roles ofbasi fri

ug ess and cohesion are, however

determination ofbasic friction in

testing.pazticular is amenable to labo ratozy

Tests carried out on naon natural joints andfor incremental rou

angles will elimina te the effects of

yt and coated surfaSuch values can be expect

y 'rent(either higher ore basic friction angles

termmed from tests on saworresiduaistren~

cut surfaces

stren~ve Geld shearDetermination of eff

requires detailed assessment ofc acteristics of dis

Some aspects of thts'rocedure have beeny 'edinCowland &

'chards (1982)sand will he furthsequ p pe y

References

1.Brown ET (1981)—Su edetenninin sh

' gshearstrengtkRockcharastm and tut -ISRM

Pergamon Press, 138-137

a..ange Mand Herget G(19 -Deternunauon ofdiscontinuities by direct

't ope manual supplement 3-2:tory tests for design

port

3.Barton NR(1973) —Reviewcriterion fo rock

'3a

r joints. En 'ineering Geology, 7,287-

4.Richards LR and Cowlandw d JW(1982).The effect of

ng Granite. Hong Kong

S.Ross-Brown DM and Walton G (19?8) Aportshljoints. Rock Mechanics, 7,

engineering- Revised6.Hock E andBray JW 198

Mining and Metallurgythird editio

7.Hencher SR and Richards LR(1982—ceo tmg)omtsm Hong Kong

ong gineer, 11(2),21-2S

8.Brown ET, Richards LR and Banstrength characteristiconference on rock eng'nearing

'cs of the Delabo le Bates. Proceng'nearing, Newcastle upon

9.Schneider HJ(1978)-The lahorat9.Schn — e ory direct sheargeotechnicsl evaluation. Bulletin

121-126'ion of Engineering Geology, 18,

10.Hencher SR(1981)-Friction'ction parameters for thepea to withstand earthquake

.Proc conference on dame and earthndon, stitutionof Civil Engin'ars,79-88

11.Gillette DR, Sture S Ko, Ko HY, Gould MC and Scott'c behaviour ofrock '

GA

Symposium on rock mechanimechanics, Texas, 163-179

12.Patton FD (1966 —M)— ultiple modes of shear failure1st international'al conference on rock

'cs, '809-813

The inflinfluence of frostheave on houses under

TydKconstruction in Merth

by IStatham, Ove Arup &Partners

I I ~L; i+I N( CEO ~ i BBNB'I

%(Irwin

Iiil iT~

~ i ~ is I iiiiLOL i w w ~ 1 Nrr ( (I 81 E

~iI ~ 'l eiIO ~ I i

e iaioi iwl ~I LXSfrts00, ".

~ 0401 LOI iiiEOLii 0 (0

, ".((w 4 i ~ 0

IntroductionThis paper considers the mechanismresponsible for crackin in

aring bzick and wereo r 1985.Foundations and

r y eendofr s were complete b therstzuctures were

p ete hy early February 1986 afrom ghxing and inteznal Gnish es.

Cracking was noticedin the ext1 '7Fn ebzuary 1986an

inspection revealed thathad heaved.

the Goor slabs

Typical damageThe houses were Grst inspected on 19

(on 19February).

Damage to the superstructures wasalthough unsightly. Crackinmainlyinth gab owing thee le ends foll

mortar joints at Grat G' 'nallyonthefrontand 31

GROUND ENGINEERING . MARCH 1989