This study is concerned with the creep characteristics of sands under constant principal stress differences of various stress levels which were experimentally obtained by drained triaxial compression tests. In these tests, in order to obtain the creep behavior which is due only to the principal stress difference, but excluding the effect of variation of mean effective principal stress, both the mean effective principal stress as well as the precompression stress of the sand specimens were kept at the same value. The results of these tests are consistent with those predicted by the equations based upon the rheological model previously proposed by Murayama (1983).

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Six series of tests were performed to investigate the effects of preshearing on the liquefaction characteristics of saturated sand samples subjected to cyclic shear stress. Five types of shear stresses were previously applied to the samples, and thereafter a constant double amplitude cyclic shear stress which had a fixed stress ratio of σ_D/2·σ₀=0.113 was applied until liquefaction occurred. Through these experiments, it was found that within the range of the tested stress level, the curves showing the relationship between the magnitude of preshear stress and the liquefaction resistance have a peak, and that this phenomenon can be attributed to the outcome of the combined effects of previous small preshear and large preshear. It was also found that this change in liquefaction resistance caused by preshearing can be explained by superposing the two characteristic effects of the same-direction and the opposite-direction preshearing.

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A consolidation test method using seepage force was previously proposed to obtain consolidation constants for very soft clayey soils subjected to very low stress. Its applicability to practice is herein examined.The main results obtained are as follows : (1) Mikasa's large strain theory well interprets the process of seepage force consolidation, and a settlement-time curve obtained from the proposed test is in good agreement with the one calculated by using the theory and the constants obtained from that test; (2) Consolidation constants obtained from the proposed tests are in good agreement with the ones determined by the traditional oedometer tests; (3) Relationships between the constants and plasticity index are quite similar to the ones obtained from the constant rate of strain consolidation tests conducted by Umehara et al.In summary, the effectiveness of the proposed test method is emphasized with several precautions in operating the test.

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A three-dimensional stress-strain relationship for loose sands having the anisotropic fabric is derived from the elasto-plasticity based on the concept of non-associated flow rule. Yield function, plastic potential function and hardening function which are required to frame the theory for sand are formulated through the experimental study on the relationship between plastic strain increment ratio and stress ratio and the plastic strain work during shear under three different principal stresses. Parameters included in the proposed elastoplastic work hardening model can be determined easily from the conventional triaxial compression and extension tests and the isotropic consolidation-swelling test.Comparisons of the predicted and measured three-dimensional stress-strain relationships showed that the proposed theory is capable of simulating the anisotropic deformability obtained by two kinds of the drained true triaxial tests in which cubical Fuji river sand and Toyoura sand specimens are used by Yamada and Ishihara (1979) and present authors, respectively.

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A triaxial device which enables static cone penetration test to be performed on sand specimens with the same stress conditions and fabric characteristics as those of static and cyclic triaxial tests is developed. In order to examine the relationship between cone penetration characteristics and static and cyclic mechanical properties of sand with any fabrics, a series of cone penetration tests, static triaxial compression and extension tests and liquefaction tests on the specimens prepared by different methods was conducted by using this apparatus. Test results showed that cone penetration resistance value depends strongly not only on the density but also on fabric characteristics of the sand specimen. It was recognized, however, that there exists a unique correlation between the penetration resistance and angle of shearing resistance or cyclic undrained triaxial strength irrespective of the fabric characteristics of the sand specimens. It was also clarified that the characteristics of dilatancy due to the cone penetration are intimately connected to those in the static triaxial test. Penetration resistance values under any effective confining stresses were calculated on the basis of the cavity expansion theory which takes account of the fabric anisotropy-dependent compressibility of sand. It could be seen that predicted penetration resistance values agree well with observed ones.

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The smectite-dominated Ariake Bay marine clay, the sensitivity of which can increase upon leaching to yield quick clay, is found to conform to the general model for quick clay development that has been proposed on the basis of the properties and behaviour of the Canadian and Scandinavian quick clays. While the Ariake Bay soil is more plastic than the Leda clay from the South Nation site, its plasticity and its yield stress at constant water content, as determined using a coaxial viscometer, decrease with salinity in the same manner. The removal of citrate-dithionite soluble materials decreases the yield stress in both soils although the Ariake Bay soil, from which more is removed, is more dramatically affected. Dispersants decrease the yield stress of both soils. Why, in contrast to most smectites, the smectites in the Ariake Bay marine clay are of low activity and have their activity decrease upon leaching, thereby allowing the development of quick clay behaviour, remains uncertain but it may be related to dominance by high-iron smectites.

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This paper presents a method to extend an elastoplastic constitutive model valid only in the triaxial compression condition to one applicable in general stress conditions. A stress-strain model in three-dimensional stresses was developed on the basis of the extended concept of the "Spatial Mobilized Plane" (briefly SMP^*). From reconsideration of the concept of theSMP^*, a mechanical quantity to describe uniquely the behavior of soils in three-dimensional stresses is obtained. This mechanical quantity t_ij is a symmetrical tensor whose each principal value is the product of the corresponding principal stress and the corresponding direction cosine of the SMP. The mechanical quantity is then applied to the Cam-clay model as an example. It is checked by various data of drained and undrained shear tests on normally consolidated clay that the t_ij Cam-clay model proposed here describes uniquely the behavior of soils not only under the triaxial compression condition but also under the triaxial extension and three different principal stress conditions. Although only the application of t_ij to the Cam-clay model is shown in this paper, t_ij is easily applicable to any other elastoplastic constitutive models for soils.

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The characteristics of the excess pore water pressure developed in a saturated cross-anisotropic elastic soil deposit immediately after the application of a load are theoretically examined. It is indicated that the excess pore water pressure is quantitatively equivalent to the increase in total vertical stress only when the elastic constants of soil skeleton have the relation of μ_h+μ_vE_h/E_v=1, and to the increase in mean normal stress only when the soil skeleton satisfies the zero-dilation condition of μ_h+μ_vE_h/E_v=1 and μ_v=0.5. Moreover, it can be found from numerical results that the excess pore water pressure is exceedingly affected by the anisotropy of Young's modulus of soil skeleton.

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Possible explanations regarding the often conflicting views on the effect of drop height on relative density of pluviated sand samples are presented. Assuming that the relative density achieved would be related to the particle energy at impact, it is shown theoretically that the drop height effects are of no significance for pluviation through water. In air pluviation, however, the relative density achieved depends very much on the drop height, although the range of drop heights over which densificiation is effective depends on the average particle size. Preliminary test results on a sand together with some test results from literature are presented in support of the ideas advanced.

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An influence of anisotropy of deformation modulus on the initial gradient of effective stress paths of cohesive soils is investigated, based on the results of a series of consolidated undrained triaxial compression and extension tests on five kinds of normally consolidated cohesive soils. The correlation of the anisotropy of deformation modulus and the initial gradient of effective stress paths in K₀ consolidated samples is then examined by assuming that the soil is a cross-anisotropic elastic body.It is found that the initial gradient of effective stress path in K₀ consolidated samples can be predicted qualitatively by introducing the anisotropic effects of deformation modulus of saturated cohesive soils into cross-anisotropic elastic body.

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