,LL &a TS5&/ Ah i G G?, Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. bAw &&c.- - SLL J 2 Canadian Geotechnical Journal Revue canadienne de T H E N A T I O N A L R E S E A R C H COUNCIL OF C A N A D A L E CONSEIL N A T I O N A L DE RECHERCHES D U C A N A D A Volume 15 Volume 15 Number 2 May 1978 numero 2 r.; mai 1978 The correlation of index properties with some basic engineering properties of soils C. P. WROTHA N D D. M. WOOD Can~bri(igeUniwrsity Engineering Depclrttnent, Trrrmpingtotz Street, Cumbridge, CB2 IPZ, Englccnd Received July 27, 1977 Accepted November 23, 1977 Experimental evidence is produced to show that i t is reasonable to assign a unique strength to all soils when at their respective liquid limits, and to redefine the plastic limit as the water content at which the strength is 100 times that at the liquid limit. Combining these assumptions with ideas of critical state soil mechanics it is then possible to relate the compression index of the remoulded soil to its plasticity index, and to suggest a unique relation between remoulded strength and liquidity index, irrespective of actual values of liquid and plastic limits. Field data from the Gulfof Mexico and from the North Sea are presented in support of these relations. The predictions of strength are best for overconsolidated clays, having water contents near the plastic limit. Recently in the United Kingdom the cone penetrometer has become the recommended test fordetermination of the liquid h i t , in preference to the Casagrande test. Having redefined the plastic limit i t would be logical to use the cone penetrometer to determine this too, by using cones with different weights. Experimental data are shown to illustrate and support this proposal. Les resultats experimentaux presentis demontrent qu'il est raisonnable d'attribuer une valeur unique de resistance i tous les sols lorsqu'ils sont B leur limite liquide respective, et de redefinir la limite plastique comme etant la teneur en eau a laquelle la resistance est de cent fois superieure 21 celle correspondant a la limite liquide. Combinant ces hypotheses avec les concepts d'itat critique de la mecanique des sols, il est alors possible d'etablir des relations entre I'indice de compression du sol remanie et son indice de plasticite, et de suggerer une relation unique entre la resistance remaniee et I'indice de liquidite, quelles que soient les valeurs des limites liquides et plastiques. Des donnees obtenues sur des echantillons du Golfe de Mexico et de la Mer du Nord sont prtsenteesal'appui deces relations. Les predictionsde la resistance au cisaillement sont les meilleures dans le cas des argiles surconsolidees dont la teneur en eau naturelle se rapproche de la limite plastique. Recemment au Royaume-Uni, le pknCtrometre conique est devenu I'essai recommande pour determiner la limite liquide de preference i~ I'essai Casagrande. Pour faire suite a une nouvelle definition de la limite plastique, il serait logique d'utiliser le pknetromitre conique pour determiner aussi cette limite au moyen de c8nes de differents poids. Des donnees experimentales sont presentees pour illustrer et appuyer cette suggestion. [Traduit par la revue] Can. Geotech. J.. 15, 137-145 (1978) Introduction The index tests, proposed by Atterberg, introduced into soil mechanics by Terzaghi and standardized by Casagrande, formed the first attempt to categorize soils regarding their main engineering properties. Because of their universal acceptance, they form an essential background to any site investigation, however simple or sophisticated it may be. AS soil mechanics has advanced and more ac- curate methods of testing soils (both in the laboratory and in the field) have been developed, less reliance has been placed on the results of index tests. Nevertheless they still play a major role in the assessment of any soil and within the experience of a soil engineer. In this paper we attempt first to relate both index tests directly to the undrained shear strength of a soil. This allows a direct quantitative correlation to be made (i) between the plasticity index and 2 Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. 138 CAN. GEOTECH. J . VOL. 15. 1978 the compression index and (ii) between the liquidity index and the undrained shear strength. These correlations lead to certain important implications for the assessment of poor quality or incomplete data for any soil. Two examples of data from offshore site investigations are reanalysed in the light of the proposed relationships. Although this interpretation is promising, it must be emphasized that this approach is not proposed as a substitute for fuller site investigation, sampling and testing, but as a framework against which various test results can be judged for their consistency and reliability. Second, we suggest that if index tests can be directly related to the undrained shear strength of a soil, then it is logical to use the fall cone test to determine these index properties. 1. Index Tests and Shear Strengths The precursors of the now widely used liquid and plastic limit tests for soils were devised by a Swedish agricultural scientist, Atterberg ( 191 1) . He originally thought of these tests as dividing the behaviour of the clay into distinct types dependent on the water content. Thus the liquid limit (flytgriinseiz) was the water content below which the soil would cease to flow as a liquid; the plastic limit (utrullgriiizser~), the water content below which the soil could not be rolled out into a thread. These limits and their difference, the plasticity index, are used to characterize different soils. Many attempts have been made to link these parameters with other soil properties (e.g. Skempton 1944; Bjerrum and Simons 1960; Seed et al. 1964a,b). Attempts have also been made to associate particular values of mean normal effective stresses with the state of the soil at the two limits, or to suggest a fixed ratio between these stresses (e.g. Casagrande 1958; Youssef et al. 1965; Schofield and Wroth 1968; Livneh et al. 1970; Russell and Mickle 1970). These attempted correlations indicate that one major soil property to which engineers attach particular importance is the undrained shear strength. In many real engineering situations, important design decisions have to be based on inadequate or poor quality data of the soil. In such circumstances it is valuable to establish some likely lower bound on the strength of the soil by assessing its remoulded strength. In the case of many natural deposits of soft normally consolidated clay, the soil is sensitive so that the remoulded strength may underestimate the in situ strength by a substantial margin. However, for heavily overcon- solidated clays, having natural water contents close to the plastic limit, there is usually little sensitivity, and the remoulded strength should form a close lower bound to the in situ strength.l The purpose of this section of the paper is to establish a relationship between the remoulded strength and the liquidity index of a soil. Shear strength of soil can be measured directly or indirectly with many different apparatus; unfortunately the precise results depend on the actual boundary conditions imposed by the type of test. In the hope of obtaining a satisfactory correlation it is advisable to standardize on one type of test; in the following discussion, strength is taken as the triaxial undrained compressive shear strength c,,. This provides a particulary simple direct measurement of strength. Casagrande, as long ago as 1939, related shear strength with the liquid limit of a soil. In the course of lectures that he gave at Harvard University at that time he suggested an average value of the shear strength of soils at the liquid limit as gf/cm","ut indicated a rel2.65 kN/m"27 atively large spread of values depending on the apparatus used for determining the liquid limit. A major difficulty in attempting to assign a unique value of shear strength to the liquid limit is the unsatisfactory nature of the basic liquid limit test in the Casagrande apparatus. The results for any particular soil can vary widely depending on such factors as the hardness of the base of the apparatus and the bench on which it stands, and the performance of the operator. Detailed investigations into the reliability and consistency of the test have been reported by Norman ( 1958 ) , Casagrande (1958) and Sherwood and Ryley (1970). Norman reports the shear strengths of five soils measured by means of a miniature laboratory vane at their respective liquid limits. Using a liquid limit apparatus with a base satisfying the British standard (at that time) the strengths ranged from 0.8-1.6 kN/m2 (8-1 6 gf/cm" whereas using an apparatus manufactured according to the American Society for Testing and Materials (ASTM) standard, the strengths ranged from 1.1-2.3 kN/m2 lWhere large movements have occwred on some preexisting slip planes in heavily overconsolidated clay the remoulded strength may overestimate the in siru strength. A residual strength, taking account of the reduction in strength resulting from particle reorientation will then be more appropriate (compare Skempton (1970) and Bishop (1971)). Wasagrande (1958) states that measurements of shear strength a t the liquid limit were made with "precision direct shear tests as well as other methods". Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. WROTH AND WOOD ( 1 1-23 gf/cm2). Skopek and Ter-Stepanian (1975) state that the shear strength of a soil at the liquid limit in the Casagrande apparatus ranges between 1 and 3 kN/m2. The results obtained by Skempton and Northey (1953) reproduced in Fig. 1 show a range of strengths (again measured using the laboratory vane test) of 0.7-1.75 kN/m2 (0.1-0.25 Ibf/in2) for four soils with very different values of plasticity index. The most comprehensive and self-consistent set of tests to be found in the literature is that reported by Youssef et al. (1965). They tested a large number of remoulded clays, measuring the shear strength with a laboratory vane as the water content was varied in the neighbourhood of the liquid limit.3 The results are shown in Fig. 2, where the shear strength is plotted against water content, each with logarithmic scales. Each straight line represents the resuits for one clay, and the solid circular point represents its state at its liquid limit. , These solid circular points lie close to a line (the LL line) that indicates a clear trend of decreasing shear strength with increasing value of the liquid limit. Over the range of liquid limit of 30-200% the range of shear strength is 2.4-1.3 kN/m3 (24-13 gf/cm2) with a mean value of about 1.7 kN/m" 17 gf/cm". Assuming that the shear strength measured by the laboratory vane is the same as that measured in the triaxial compression test, this mean value of 1.7 kN/m"ill be adopted as the present best estimate of the undrained shear strength c,, (in triaxial compression) of a soil when at the liquid limit. From the evidence of Skempton and Northey (1953) in Fig. 1 it will be assumed that the shear strength at the plastic limit is 100 times that at the liquid limit. A best estimate of 170 kN/m2 will be adopted. Strength is commonly plotted against water content w on a semi-logarithmic plot and an approximately straight line relationship is obtained: [I] w + A In c , = constant where A is a constant. If a,' and a,' are the axial and radial effective stresses in the triaxial test, we can define the state of a triaxial sample by means of two stress parameters (deviator stress q = 3Youssef et al. d o not state whether the liquid limit apparatus used was constructed according to the British o r to the American standard. LL R PI Plplociq 30 16 14 0.35 ILXT~T 73 25 48 0.96 WIWm 97 32 65 1-27 Clay Hortan FIG. 1. Relation between shear strength and liquidity index of remoulded clays (after Skempton and Northey 1953). 60 80 K X ) l X ) 1 4 3 ~ 233 water content % 40 FIG.2. Relation between water content and shear strength. Each line represents a different soil. T h e solid points indicate the shear strengths at the liquid limit (after Youssef er a/. 1965). + - a,' and mean normal stress p' = (a:,' 2ar1)/3) and one volumetric parameter, the current water content w, the voids ratio e or the specific volume V of the soil. These last parameters are related for saturated soil by a,' where G, is the specific gravity of the soil particles (typically about 2.7), and the water content is expressed as a ratio, not as a percentage. Roscoe et al. (1958) found that the ultimate states of remoulded soil in drained and undrained triaxial tests lay on a line in pl:q: V space, which has since been called the critical state line (Fig. 3 ) . When these ultimate states were reached in monotonic loading, the soil could be sheared with no further change in effective stresses or volume. The critical state line is described by [31 and I/ + A In p' = constant 140 C A N . GEOTECH J. VOL. IS. 1978 [41 q = MP' It was found that this critical state line (CSL) was parallel to the normal consolidation line (NCL) in V : In p' space (Fig. 3 ) so that x = C,'/ln 10 Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. [51 where C,' is the compression index of the remoulded soil. For triaxial compression the parameter M is related to the angle of internal friction +' of the material by [61 M = 6 sin +'/(3 - sin +') In an undrained triaxial compression test the value of q on the CSL is q = 2c,, [71 and hence, combining [3], [4] and [7], we find that V [81 + h In c , = constant Noting [2], we may compare this with [I] in order to deduce that A = A/G, [91 so that [lo] w + (h/Gs) In c,, = constant If, in the light of the evidence of Skempton and Northey (1953), we redefine the plasticity index (PI) as the change of water content (expressed as a ratio) producing a 100-fold change in strength, then, from [lo] 11 or, from [5] [I21 h = (PI G,)/ln 100 C,' = *PI G, and for G, = 2.7 C,' = 1.35PI The consequence of the assumptions (i) of certain strengths associated with the liquid and plastic limits, and (ii) of the linear relationship between w and log c,, is illustrated in Fig. 4 in which the remoulded strength (on a logarithmic scale) is plotted against the liquidity index (LI). The advantage of using the latter parameter is that this diagram should apply to all soils, irrespective of the actual values of liquid and plastic limits. The diagram in Fig. 4 is directly comparable with, and is an idealization of Fig. 1. The remoulded strength can be estimated for any value of the natural water content of a soil by interpolation between points L and P in Fig. 4. By definition of the liquidity index, and from the linear relationship C 141 LI = ( W - PL)/(LL - PL) = (In 170/c,,) /ln 100 whence [15] c, = 170 exp (-4.6LI) kN/m2 It is possible, but probably not worthwhile, to refine this expression to take account of the variation of shear strength with liquid limit as follows: [ 161 c,, = 100cI.I, exp (-4.6LI) where cl,~,is the undrained shear strength at the liquid limit obtained from the work of Youssef et al. (1965) plotted in Fig. 2. Because of its form, the relationship [15] sensitive to any inaccuracy in the determination the liquidity index. Differentiating [15] gives [171 6c,,/c,, = -4.6 6 (LI) so that an error of 0.1 in LI would give rise to error of 46% in the estimate of c,,. An error of 0.1 in the liquidity index is a large Liquid, Limit FIG. 3. Critical state line in p l : q : V space. FIG.4. Idealized relationship between liquidity index and shear strength. 14 1 Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. WROTH A N D WOOD one, which is unlikely to arise in practice. For soil samples with natural water contents close to the liquid limit the estimate of the (very low) remoulded strength may be misleading, but these will be the soil deposits that tend to be sensitive, and for which the estimates of the remoulded strength would be inappropriate anyway. For soils with natural water contents nearer the plastic limit, the errors in determining the (low) liquidity index are likely to be smaller. However, it must be appreciated that the estimates of strength are sensitive to these errors. 2. Reanalysis of Field Data In searching the literature for data to be reanalysed there are few sites for which reliable profiles of both consolidation and shear strength results are available. Two groups of data from offshore sites are rcanalysed here. The first set of data is that quoted by McClelland (1967) for cores obtained in the Gulf of Mexico, and this is analysed regarding consolidation behaviour for values of the compression index. From the plasticity index PI the gradient A of the normal consolidation line is calculated from [I 11 to give a value of 0.585PI for G, = 2.7. The correlation between measured and predicted values of A is shown in Fig. 5 and is reasonable, although there is some scatter. Data from 12 locations are shown. The second set of data is from some borings in the North Sea; the results are interpreted to give an estimate of the strength profile. These clays all have plasticity indices in the range 0.25-0.30. From the measured values of liquid limit, plastic limit and natural water content, the liquidity index has been calculated, and then substituted into [15] to give an estimated value of the shear strength. Figure 6 shows predicted and measured shear strength profiles for four North Sea borings. The agreement between the predictions and measurements is surprisingsly good. It has already been noted [I71 that the prediction is rather dependent on the accuracy of the liquidity index, which in turn depends on the accuracy of the index tests and the measurement of the natural water content. However, the liquidity indices of nearly all the results are within the range 0-0.3 so that the soils in question are all heavily overconsolidated, and hence will show little if any sensitivity; the estimated remoulded strengths are likely to agree with the measured values obtained from disturbed samples. L Oo 0.I 0.2 0.3 pmdicteci h 0-4 05 FIG.5. Comparison of measured and predicted values of compression index (data from McClelland 1967). 3. Use of the Fall Cone to Determine Index Properties4 If the index tests are to be interpreted as a measure of strength, then it is logical to use a test that is as simple as those devised by Atterberg, but one that measures strength more directly. Fall cone tests have been used in some parts of the world for many years as a quick measurement of strength. Hansbo (1957), in particular, reported a very thorough study of the relationship between cone penetration and strength (measured by means of a vane test), for different cone angles and weights. He showed that the relationship depends on the sensitivity of the clay and on the way in which it is sampled. However, he demonstrated that, once the appropriate relationships were known, a good agreement was in general obtained between estimates of strength made using the cone and using other shear strength tests. In the new edition of the British standard Methods of test for soils for civil engineering purposes: BS 1377 (British Standards Institute 1975), a variant of the fall cone test (there called the cone penetrometer) is given as the method to be used for measuring the liquid limit in preference to the Casagrande apparatus. In this recommended cone penetration test the liquid limit is defined as that water content for which a standard cone of apex angle 30° and 4This section builds on unpublished work carried out by G . W. E. Milligan at Cambridge University Engineering Department in 1971, and also on suggestions made by -A. N. ~chofield. CAN. GEOTECH. J. VOL. 15. 1978 shear s t m n g . Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. Q ' . shear strength XX) ZO I 0 00 k ~ . 330 d k ~ l r n ~ 300 FIG.6. Profiles of measured and predicted strengths with depth a t four North Sea locations. weight 0.78N (80 gf) will penetrate 20 mm when allowed to drop from a position of point contact with the soil surface (Fig. 7 ) . This test was shown by Sherwood and Ryley (1970) to give a more consistent estimate of the liquid limit than the Casagrande apparatus, with greater repeatability and less operator susceptibility. If we perform a series of cone penetration tests on soils at different water contents we may expect that the depth of penetration d (Fig. 7 ) of the cone will be dependent on the strength of the clay. For a cone of weight W we could expect from dimensional analysis that [I81 cud2/W = constant Hansbo (1957) also derived [18], with rather more detailed consideration of the mechanics of the cone penetration, and provided experimental evidence to support its validity. He stated that the constant depends mainly on the cone angle but is also influenced by the rate of shear and by the sensitivity of the clay. Hansbo was interested in using the cone to determine strength and gave values of the constant in [18] in order that strengths of different clays might be obtained. We, however, are here concerned to assign a particular strength to a particular penetration of a standard cone and then proceed to make further statements about the characteristics of the soil. Accepting [18], and using equation [lo], we WROTH AND WOOD Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. eight soil FIG.7. Diagram of fall cone test. could expect that a plot of water content w against d for a constant cone weight would produce a line [19] w - (2h/Gs) In d = constant which would be straight on a semi-logarithmic plot (Fig. 8) with gradient [201 2X/Gs = 2C,'/G, I11 10 and for G, = 2.7 [211 2X/Gs = 0.322C,' There may be dynamic effects, associated with the penetration of the cone, which will vary with the depth of penetration. However, if we use geometrically similar cones of different weights and find the water contents for which the penetrations are the same, then it follows from [18] that [22] c,,/ W = constant (for fixed d ) We can compare our estimate in Sect. 1 of the shear strength at the liquid limit with that computed from Hansbo's (1957) tables. For undisturbed clay tested with a 30" cone, at 20 mm penetration he gave c , = 9.91 kN/m2 for a 3.92 N (400 gf) cone and 2.45 kN/m2 for a 0.98 N (100 gf) cone. These strengths are roughly in the expected ratio (4: 1 ) of the cone weights and indicate a strength of 1.96 kN/m2 for a 0.78 N (80 gf) cone. For remoulded clay, Hansbo tabulated data only for the 60" cone, but he also showed a linear relation between the penetrations of a 0.98 N/30° (100 gf/30°) and a 0.59 N/60° (60 gf/60°) FIG. 8. Diagram of fall cone results with different cone weights. 143 cone: 20 mm penetration of the former is equivalent to 7.7 mm penetration of the latter. Entering his table with this figure produces a strength for the 0.98 N/30° (100 gf/30°) cone of 2.94 kN/m2 corresponding to 2.35 kN/m2 for the 0.78 N/30° (80 gf/30°) cone. These figures can be compared with our single estimate for the strength at the liquid limit of 1.7 kN/m2. In the Soviet Union, Vasilev developed the use of the fall cone test as a means of determining the liquid limit of a soil, which became standardized in the USSR in 1949. The Vasilev test defines the liquid limit as the water content of a soil sample in which the standard cone of 30" apex angle and weight 0.74 N (76 gf) penetrates to a depth of 10 mm in 5 s. Unfortunately this definition of the liquid limit is very different from that of the original Casagrande standard or the revised British standard. Skopek and Ter-Stepanian ( 1975) attribute a shear strength of 8.5 kN/m"o the Vasilev test (i.e. between three and four times the strength of the Casagrande test). However, although the definition is different, the results are seen to be consistent. For the Vasilev test c,, = 8.5 kN/m2, d = 10 mm and W = 0.74 N (76 gf) so that using the dimensional analysis of [I81 the shear strength attributed to the British standard fall cone test (with a geometrically similar cone) having d = 20 mm and W = 0.78 N (80 gf) would be c,, = 8.5 (80/76) (102/209 = 2.24 kN/m2. From [18] and [19] we would expect that a separate line relating w and d would be obtained for each weight of cone, but two cones of weights WI and W2 should yield parallel lines with a water content separation (Fig. 8) of and hence, from [ l I.] Accepting the definition given earlier of plasticity index as the change of water content producing a 100-fold change in strength of the soil then it would make sense to use the same strength measuring test to determine both liquid and plastic limits. It is not feasible to use a cone of weight 78 N (8 kgf) for comparison with the 0.78 N (80 gf) cone specified for the liquid limit (which would then give W1/W2 = 100 and PI = A). However, satisfactory tests have been obtained using a 2.35 N (240 gf) cone, giving a weight ratio W,/W2 = 3. Results of such fall cone tests on Cambridge Gault clay are shown in Fig. 9. 144 C A N . GEOTECH. J. VOL. 15, 1978 cone weight Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. 0.d -1 $09' 2' I I 5 10 20 cone p ~ n e t r a t ~ o nd rnm sb FIG.9. Results of fall cone tests on Cambridge Gault clay. Straight parallel lines have been drawn through the two series of points. The gradient of the lines, from [19], is For a value of G, = 2.75 this leads to a value for the compression index of the remoulded Gault clay, C,' = 0.70. The spacing between the pair of lines provides an independent check on this value of C,' (from [23]): Moreover the redefined plasticity index (in terms of the 100-fold increase in strength) is given by 1241 as PI = 2A/10glo 3 = 0.52 (or 5 2 % ) . This should be compared with a value of PI of 54% obtained by the conventional method. Thus the use of the fall cone penetration test provides a simple means of determining values of the index properties logically redefined simply and directly in terms of the undrained strength of the soil. Conclusions The purpose of this paper has been to develop correlations between the results of index tests and the two basic properties of a soil, its shear strength and compression index. The estimates of undrained shear strength depend only on the liquidity index, and those of compression index only on the plasticity index. It has been shown that such correlations allow reasonable estimates to be made of these properties for the soil when in a remoulded state. As a consequence such estimates will be conservative and should lead in general to lower bounds to the actual in situ strength and compressibility. The correlations have particular application to offshore site investigation, where good quality samples and test results are very difficult and expensive to obtain. Such samples that are obtained are likely to be in a disturbed state. The correlations also have application generally in forming a background against which test results can be checked for their consistency and reliability, and to suggest whether a particular soil may have unusual properties that need further investigation. Although the interpretation of results from two offshore sites looks promising it must be emphasized that this approach cannot be a substitute for proper site investigation, sampling and testing; it is meant to be an adjunct that should increase the engineer's confidence in his judgement of the properties of a soil. The concepts, and results, clearly show the value of the fall cone test, and its superiority over the Casagrande apparatus for determination of the liquid limit. It is hoped that the rationale for redefining the plastic limit as that water content that gives a 100-fold increase in shear strength over that at the liquid limit, and its measurement via the fall cone test will soon be adopted. ATTERBERG, A. 191 1. Lerornas forh5llande till vatten, deras plasticitetsgriinser och plasticitetsgrader. Kungliga Lantbruksakademiens Handlingar och Tidskrift, S0(2), pp. 132-158. BISHOP,A. W. 1971. The influence of progressive failure on the choice of the method of stability analysis. Geotechnique, 21(2), pp. 168-172. BJERRUM, L., and SIMONS, N. E. 1960. Comparison of shear strength characteristics of normally consolidated clays. Proceedings, ASCE Research Conference on Shear Strength of Cohesive Soils, Boulder, CO. pp. 71 1-726. BRITISHSTANDARDS INSTITUT~ON. 1975. Methods of test for soils for civil engineering purposes. BS 1377: 1975. CASAGRANDE, A. 1958. Notes on the design of the liquid limit 8(2), pp. 84-91. device. Geotechniq~~e, HANSBO,S. 1957. A new approach to the determination of the shear strength of clay by the fall-cone test. Royal Swedish Geotechnical Institute, Proceedings No. 14. L I V N E HM., , KINSKY, J . , and ZASLAVSKY, D. 1970. Correlation of suction curves with the plasticity index of soils. Journal of Materials, S(1). pp. 209-220. MCCLELLAND, B. 1967. Progress of consolidation in delta front and prodelta clays of the Mississippi River. I n Marine geotechnique. Editeclhy A. F. Richards. University of Illinois Press, Urbana. IL pp. 22-40. NORMAN, L. E. J . 1958. A comparison of values of liquid limit determined with apparatus having basesofdifferent hardness. Geotechnique, 8(2), pp. 79-83. ROSCOE,K. H., SCHOFIELD, A. N., and W R O I HC. , P. 1958. On the yieldingof soils. Geotechnique, 8(1), pp. 22-52. RUSSELL, E. R., and MICKLE, J . L. 1970. L i q ~ ~limit i d values by soil moisture tension. ASCE Journal of the Soil Mechanics and Foundations Division, 96(SM3), pp. 967-989. Can. Geotech. J. Downloaded from www.nrcresearchpress.com by University of Waterloo on 09/10/13 For personal use only. WROTH AND WOOD SCHOFIELD, A. N., and WROTH,C. P. 1968. Critical state soil mechanics. McGraw-Hill, London, England. 310 p. SEED,H. B., WOODWARD, R. J., and LUNDCREN, R. 19640. Clay mineralogical aspects of the Atterberg limits. ASCE Journal of the Soil Mechanics and Foundations Division, 90(SM4), pp. 107-131. 19646. Fundamental aspects of the Atterberg limits. ASCE Journal of the Soil Mechanics and Foundations Division, 90(SM6), pp. 75-105. SHERWOOD, P. T., and RYLEY, M. D. 1970. An investigation of a cone-penetrometer method for the determination of the liquid limit. Geotechnique 20(2), pp. 203-208. SKEMPTON, A. W. 1944. Notes on the compressibility of clays. Quarterly Journal of the Geological Society of London 100 C: Parts 1,2, pp. 119-135. -1970. 145 First-time slides in over-consolidated clays. Geotechnique, 20(3), pp. 320-324. SKEMPTON, A. W., and NORTHEY, R. D. 1953. The sensitivity of clays. Geotechnique, 3(1), pp. 30-53. .I. and , TER-STEPANIAN, G. 1975. Comparison of liquid SKOPEK, limit values determined according tocasagrande and Vasilev. Geotechnique. 25(l), pp. 135-136. YOUSSEF,M. S., EL RAMLI,A. H., and EL DEMERY, M. 1965. Relationships between shear strength, consolidation, liquid limit, and plastic limit for remoulded clays. Proceedings of the 6th International Conference on Soil Mechanics and Foundation Engineering, Montreal, P.Q., Vol. I, pp. 126-129.
