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NOTES

Correlation between standard penetration test values and overburden pressure fordesert sands

N A BI L . I SMA E L

Civil Erzgirzeerirzg Department, K~ c~c i i r niversi ty, P. 0. Bos 5969, Sclfit, Kicrvnit

A N D

A . M . J E R A G H , . A . K H A L I D I , N D M . A . MO L L A H

Go vern men t Lubor ntor ies nrzd Testirzg Statio n, Ministry of' P~lOlic Wo rks , Kulcxiit

Received November 20 , 1987

Accepted March 17, 1988

The influence of the effective overburden pressure on the stand ard penetration test (SPT) values in calcareous desert sands isexamined by field tests. A simple field testing procedure is proposed and e n~ pl oy ed n Kuw ait at five sites having differentrelative densities for the surface soils. The correction factors for the SPT are determined from test results and compared withthe most reliable correlations for clean silica sand.

Key words: field tests, plate bearing tests, overburden pressure, standard penetration test, correction factors, relativedensity, calcareous soils, shear strength, compressibility.

L'influence de la pression effective des terres sus-jacentes sur les valeurs de SPT (essais de pCnCtration standard) dans lessables de calcaire du desert est exam inte au mo yen d'essais en place. Une procid ure simple d'essa is en place est proposCe e t aCtC utilisCe au Kuw ait sur cinq sites ay ant diffkrentes densitCs relatives dans les sols de su rface. Les facteurs d e correction pou rle SPT sont dCterminCs en partant d es rksultats d'essais et sont comparCs avec les corr6lations les plus fiables pour les sab lesIavCs de silice.

Mots elks : essais en place, essais de plaque, pression des terres sus-jacentes, essai de pCnCtration standard, facteurs decorrection, densit6 relative, sols de calcaire, rksistance au cisaillement, compressibilitC.

[Traduit par la revue]

Can. Gcotcch. 1. 25. 590-593 (1988)

Introduction

The correction of standard penetration test (SPT) results toaccount for the effect of overburden pressure has become animportant step for the proper calculation of settlement on s andand liquefaction potential. Since the work of Gibb s and Holtz(1957), several formulae and charts for making the correctionhave been published. Liao and Whitman (1986) have reviewedthe published correction factors and proposed a simple formu lafor calculating the overburden correction factor based on labo-ratory-controlled and field test data. They indicated that theexperimental data available are mainly for clean silica sand,and recommended further research for other soil deposits.

This note introduces a simple field testing procedure adoptedfor the determination of the influen ce of effective overburdenpressure on SPT N values for calcareous fine desert sands. T heprocedure was employ ed at five sites in Kuwait having d iffer-ent relative densities for the surface deposits. Test results arepresented and the correction factor is compared with the mostreliable correlations fo r clean fine sands.

Soil conditions

The five sites selected for testing were all located in the cityof Kuwait in flat open areas. T he soil conditions are describedin several recent publications (Ismael 1985; Ismael et al. 1986,1987). Briefly, the soil profile consists of an upper layer ofcompact, relatively dry fine nonplastic calcareous windblown

dune sand with little silt. This is underlain by a more comptent marine-deposited, slightly plastic cemented calcareosilty sand known locally as gatch. Figure 1 shows the soil prfiles at the test sites. AS shown, the SPT increases gradualwith depth from loose or med ium den se at the surface to denor very dense at a depth of 6- 7 m. Prior to field testing a thlayer of 0. 5 m w as removed to ensu re that testing is carried oon clean natural ground. The physical properties of samplrecovered at the test level of 0.5 m a re summarized in Table Th e relative density varied from 19 % for site 1 to 85% fsite 5. However, the surface soils are remarkably uniformbeing classified as SP - SM according to the Unified SoClassification System.

Program and procedure of field testing

At each site SPT tests were carried out directly on the grousurface at applied overburden pressures of 0, 50, 100, 15200, and 280 kPa. The tests were located along a straight liat 10 m intervals and were repeated along a parallel line 10apart. To carry out a test with overburden pressure a set three steel plates 0.76, 0.61, and 0.46 m in diameter weplaced in a pyramid fashion on the levelled ground surface shown in Fig. 2a . Each plate is 25.4 mm thick and has65 mm diam eter hole in the centre. A 44 5 kN capacity holloram hydraulic jack with a 65 mm diameter centre hole wplaced on top of the plates. Reaction was provided by a sim p

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NOTES 591T A B L E . Physical properties and penetration test results

SP T values (blow s/0.3 ni) at applied

overburden pressure (kPa):Moisture content -ybulkv

?dry-ymaxt yminf Relative density

Area, site No. w (kglm" (kg/m3) (kg/m3) (kg/m3) RD' (% ) 0 50 100 150 200 280

Sulaibikhat, 9.8 1721 1567 1800 1520 19 3 z 4 : 6 7

site 1

Sulaibikhat, 3.3 1685 1631 1783 1574 30 8 10 12 15 22

site 2

Sulaibikhat, 2.5 1724 1682 l 800 1580 49.6 15 19 21 27 3 4 4 0

site 3

Yarmouk, 3.0 1772 1720 1795 1564 70 20 24 28 34 39 49

site 4

Qurtuba, 2.8 1799 1750 1798 1520 85 25 31 37 39 48 58

site 5

'Average of three tests.'As per ASTM D 2019 using the dry method for maximum density.:Not measured.

S u l a i b i k h a t Y a rm o ukQ u r t u b a

I I I

s i t e l s i t e 2 s i t e 3 s i t e 4 s i t e 5

n W i n d b l o w n S a n d : B r o w n C a l c a r e o u s D r y F i n e S a n d w i t h T r a c e s of si ltC o a r s e S a n d ( S P - SM )

B r o w n i s h G re y C a l c a r e o u s S i l ty F i n e to M e d iu m C e m e n t e d S a n d( S M - S C )

* S P T V a l u e ( B l o w s / 3 0 cm U n l e s s O t h e r w i s e I n d ic a t ed )

FIG.1. Soil profiles at the test sites

loading frame consisting of two 4 m rigid channels weldedtogether back-to-back leaving a clearance of 70 mm. Twoground anchors were implanted until refusal using a CM E750-XL drill rig. Th e anchors were bolted to the loading frameas shown in Fig. 26. Th e tests were carried out by first apply-ing a selected overburden pressure to the soil by jacking. Th epressure was read by a calibrated pressure ga uge. T he standard51 mm diameter sampling spoon was lowered down throughthe holes in the jack and plates. A fter the first 150 mm of pene-tration considered as seating as per ASTM D-1586, the numberof blows for the following 300 mm of penetration wasrecorded. The results were obtained using the standard donut-type hamm er with a rope and cathead system with two turns of

the rope. Although this corresponds to a reduced deliveredenergy to the roads compared with the theoretical maximum(Skempton 1986), it will not affect the correction factor desiredherein, which is a ratio between two measured SPT values.

Limiting the size of the area over which the pressure isapplied to 0.76 m was imposed by practical considerations.Assuming that the stress decreases with depth below the centerof the plate according to elastic theory, the applied pressurewas increased by 5.4% to balance the loss over the first150 mm seating. With this adjustm ent the average reduction inpressure over the test zone , calculated as 8 % ,was considered atolerable error. Had the plate size been increased to 1 m indiameter, the average reduction of pressure within the test

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592 C A N . GEOTECH. J. VOL. 25, 1988

FIG.2. (a) Setting up for a field test. (b) Test setup prior to SPT test with overburden pressure.

depth would have been limited to 4 % .Grou ndwa ter at the test sites was located well below the sig-

nificant zone below th e test plate. As show n in Fig. 1 thehighest groundw ater was enco untered at site 1 at 1 .5 m belowthe test level. In situ density and moisture content were deter-mined in each test on both sides of the plate before applyingthe surcharge as per ASTM D-2922 using Troxler Nuclearapparatus model 341 1-B. A sum mary of the pene tration testresults is given in Table 1.

Analysis of test results

The relationships between the SPT and relative density forthe applied pressures employ ed are plotted in Fig. 3. The curveshown by the dotted line implied by the Terzaghi and Peck(1948) chart is located between the curves corresponding toapplied pressures of 100 and 200 W a . It deviates toward s the200 kPa cu rve at large relative densities. The ap plied pressuresindicated in Fig. 3 and Table 1 do not include the first 1 50 mmof soil and the weight of the plate assembly. Both impose asmall pressure of 7 kPa, which was neglected in the analysis.

The preceding results indicate that the adoption of the280 kPa effective overburden pressure by Tomlinson (1969)for correcting the SPT values is not justified for calcareous

sands. The use of an effective overburden pressure of 100 kPaas a standard by Peck et al. (1974) is more appropriate. Thecorrection factor CN s determined using the equation

where NI is the corrected SPT to an effective overb urden pres-sure 8, of 1 kg/cm2 (1 ton/ft2) and NSPT s the measured pene-tration resistance.

Values of the correction factor at different overburden pres-sures were calculated from test results as the ratio of the SP T atthe reference pressure of 1 kg/cm2 ( - 100 kPa) to the SP T atthe applied pressure in question. In Fig. 4 is shown a comp ari-son between the field test results and the fo llowing form ula byLiao and Whitman (1986):

Overburden

Pressure

28 0 k Pa

0 I20 40 60 80 100

Relative Density ( " l o )

FIG.3. Correlation between SPT, relative density, and effectivoverburden pressure from field tests on desert sands.

[2] CN= (a, in kg/cm2 or ton/ft2)

which is a special case of the more general equation

where K is a parameter to be obtained by fitting to test dataEquation [2] fits closely most of the reliable and accura

correlations for clean silica sand (e.g., Bazaraa 1967; Pecet al. 1974; Seed 1979 based on the data from Marcuson anBeiganousky 1977a, b; Jamiolkowski et al. 1985).

A close examination of Fig. 4 reveals that the field data focalcareous sands coincide with the correlation given by [2] fir ; r 100 Wa . For avbetween 0 and 100 kPa, the correlatiofactor is smaller than the corresponding values for clean sand

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C o r r e c t io n F a c t o r C N C o r r e c t io n F a c t o r C N

FIG. . Comparison between the SPT correction factors for cal-careous sand with the proposed formula for clean silica sand(1 kg/cm2 = 100kPa).

and increases almost linearly from 1 to 1.4 as 8, decreasesfrom 100 to 0 kPa at the ground surface.

A similar conclusion is reached when comparing test resultswith the most recent correlation proposed by Skempton (1986)for sandy soils. The correction factor CN proposed for finesands of medium relative density and for dense coarse sands isgiven by [4] and [5] respectively:

Figure 5 shows a comparison between the present test data

on fine sands and [4]. It should be noted that the Skempton cor-relation yields values for CNclose to those given by [2].

The smaller correction factor obtained herein at low overbur-den pressure of 0- 100 kPa can be attributed to the increasedcompressibility and the lower deformation modulus of calcar-eous sands compared with normal silica sand (Poulos et al.

1982). The presence of 10-20% carbonates in the surfacedeposits of desert sands (Ismael et al. 1986) in Kuwait and theArabian peninsula causes increased compressibility, which hasa significant effect in tests with little or no overburden pressure(Ismael and Vesic 1981). Thus the increase in the SPT valueswith overburden pressure is not as large as in silica sand up to acertain point (a, = 100 P a ) as less interparticle friction ismobilized. Beyond this point both sands show similar behav-

FIG..Comparison between test results and Skempton correlationfor fine sands (1 kg/cm2 = 100 kPa).

iour. It should be noted that the present results are applicable tocalcareous sand of low carbonate content. Offshore deposits ofcarbonate sands, having a large percentage of carbonates(40-80%) usually, are more compressible and may behave ina different manner.

Conclusions and recomm endations

A simple field testing procedure is introduced for the deter-mination of the influence of the effective overburden pressureon the SPT values. Field testing was carried out at five sites inKuwait with different relative densities for the surface andnear-surface soils. Based on test results, the following conclu-sions and recommendations are made:

1. The SPT overburden correction factors for calcareous

desert sands coincide with the recommended factors for cleansands ( [2]) for 8, 2 100 kPa. For a, = 0- 00 kPa, smallercorrection factors were found, increasing linearly from 1 for8, = 100kPato 1.4foriiv= 0.

2. The smaller values of the correction factor at low over-burden pressure are due to the increased compressibility of cal-careous sands compared with clean silica sand.

3. The present tests on calcareous desert windblown sandsindicate that an appropriate value of the effective overburdenpressure employed as a standard for correction is 100 @a.

4. It is recommended to carry out the field testing procedurepresented herein with increasing frequency at other-sites wheregranular deposits exist. This is to determine the influence ofthe effective overburden pressure on the SPT values and the

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59 4 C A N . GEOTECH. J . V O L . 25. 1988

necessarv cor rect ion factors . The late diamete r should or e f e r - LI AO , . S . C . , and W HI TM AN ,. V. 1986. Overburden correctio

ab ly be inc reased to 1 m if suf f ic ient react ion can be prov ided.

B A Z A R A A ,. R. S . 1 967. Use of the standard penetration test for esti-mating settlements of shallow foundations on sand. Ph.D. thesis,University of Illinois, Urbana, Urbana, IL.

GIBB S, . J ., and HOL TZ,W. G. 1957. Research on determining thedensity of sands by spoon penetration testing. Proceedings of the

4th International Conference on Soil Mechanics and FoundationEngineering, London, Vol. 1, pp. 35-39 .

ISM AE L, . F. 1985. Allowable pressure from loading tests onKuwaiti soils. Canadian Geotechnical Journal, 22 : 15 1- 57 .

ISMA EL, . F. , and VESIC,A. S . 1981. Compressibility and bearingcapacity. ASCE Journal of the Geotechnical Engineering Division,107: 1677-1691.

I SMAEL, . F . , JERA GH, . M . , MO LLAH , . A, , and AL- KHAL I DI ,0 . 1986. A study of the properties of surface soils in Kuwait. Jour-nal of the Southeast Asian Society of Soil Engi neering , 17 : 67-87.

I SMAEL, . F . , AL- K HALI DI ,. , and MO LL AH , . A. 1987. Satura-tion effects on calcareous desert sands. Transportation ResearchRecord, No. 1089: 39-48.

J A M I O L K O W S K I ,. , BA LDI, . , BELLOT.I .I , . , GH ION NA ,., andP A S Q U A L I N I ,. 1985. Penetration resistance and liquefaction of

sands. Proceedings of the 1 lth International Conference on SoilMechanics and Foundation Engineering, San Francisco, Vol. 4,pp. 1891 -1896.

factors for SPT in sand. ASCE Journal of Geotechnical Engineering, 112: 373-377.

M A R C U S O N ,. F. , 111, and BIEG AN OU SK Y,. A. 1977n. Laboratorstandard penetration tests on fine sands. ASCE Journal of the Geotechnical Engineering Division, 103: 565 -588.

19776. SPT and relative density in coarse sands. ASCE Jounal of Geotechnical Engineering, 103: 1295- 1039.

PECK, . B. , HAN SON , . E . , MOL THORN BURN, T. H. 1974. Foundation Engineering. 2nd ed. Wiley, New York, NY.

P o u ~ o s , . G . , UE SU G I,M ., and YO UN G, . S. 1982. Strength andeformation properties of Bass Straight carbonate sands. Journal othe Southeast Asian Society of Soil Engineering, 13: 189 -21 1.

SE ED , . B. 1979. Soil liquefaction and cyclic mobility evaluation folevel ground during earthquakes. ASCE Journal of the Geotechnical Engineering Division, 105: 201 -255.

SKEMFTON, . W. 19 86. Standard penetration test procedures and theffects in sands of overburden pressure, relative density, particlsize, ageing and o verconsolidation. GCotechnique, 36: 425 -447

T E R Z A G H I ,. , and PECK,R. B. 1948. Soil mechanics in engineerinpractice. 1st ed. Wiley, New Yo rk, NY.

T O M L I N S O N ,. J. 19 69. Foundation design and construction. 2nd edPitman, London, England.

Postsurcharge secondary compression equation for clays

EULALIOU A R E Z - B A D I L L O

Grncl~rateScllool of Etzgitzc>ering,Nc/tiotzcil Utliversity of MMico, Tqntlco 3 2 , Coyo~iccitl,04030- Mhico . D.F. , Metico

Received June 30, 1987Accepted January 20 , 1988

A general time - volunie change eq uation for soils is used to describe the initial swelling and further secondary compressionof clay samples when surcharges are used. The procedure is illustrated by a practical application to MCxico City clay.

Key ~vordS: lay, secondary compression, secondary consolidation, postsurcharge, time-dcpcndent compression. constitutiveequations.

Une Cquation gintralc temps - changenient de volume pour les sols est utilisdc pour ddcrirc le gonflenient initial et lacompression secondaire subsdquente d'Cchantillons d'argilc lorsque des surcharges sont appliqudes. La procCdure est illustrdcpar une application pratique sur I'argile de la ville de MCxico.

Mots cl6s : argile, compression secondaire, consolidation secondaire, postsurcharge, compression en fonction du temps,Cquations de coniporternent.

[Traduit par la revue]

Can. Gcotcch. J . 25, 593-599 (1988)

Introduction

A general t ime - volume chang e equa t ion f or so i l s ( JuArez-

Badi l lo 1985a) desc r ibes the s econdar y behaviour o f s a tur ated

plast ic so il s . Th e equa t ion as sume s the ex is tence of a l im i t ing

compr es s ion cur ve a t r = co. Th e r a te a t which the chang e in

volume takes p lace i s f ound apply ing a general philosophical

pr incip le that has a l so been appl ied to o the r phys ica l phenom-

ena ( Jua r ez- Badi llo 19856) . The equa t ion r eads

w h e r e A V = v o l u m e c h a n g e a t t i m e t , (AV)T = t ot al v o l u n

c h a n g e a t r = co, * = char ac te r i st i c t ime f o r which U = 0 . 5

an d 6 = coef fic ien t o f vo lum e v iscos i ty .

Equa t ion [ I ] in t e r ms of vo id r a tios may be wr i tt en as

\ /

wher e Ae an d ( Ae) T a r e the vo id r a tio change s a t t imes t a n d 0

respectively.

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