Using a simple displacement field the vertical movement of a round pile embedded in a uniform deposit of normally consolidated clay and subjected to a concentric vertical load is analysed. It is assumed that the clay follows a plastic-rigid (in a broad sense) constitutive law relating strain to effective stress and that the pile behaves, essentially, as a rigid unit. The influence of the shape of stress-strain behaviour of the clay, the shape of stress paths obtained in an undrained test and the response of the soil deposits below the tip of the pile on the load-settlement characteristic of a pile is analysed and discussed.

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Resulting from application of irregularly repeated loading over a long term period, an appreciable plastic displacement has often been observed in grounds and earch structures. In the present paper, a method for predicting this kind of plastic strain of soils under repeated loading is pursued using triaxial and modified oedometer tests. In the first half part of the paper, time-dependent deformation characteristics were examined through the repeated triaxial tests on a compacted sandy soil. Test results show that the deformation of soil due to repeated loading is fairly attributed to the plastic strain. Except at the beginning and in the vicinity of the failure region of number of load cycles, the ratio of plastic strain to total strain is extremely increased in the logarithm of number of load cycles. In the latter part, specially devised oedometer tests and triaxial creep tests under repeated loading were performed on various kinds of remolded and undisturbed cohesive soils. Arranging these test results, an approximate law was found out for the plastic strain performance. This law seems to be independent of the kind of soils and the loading conditions, and, therefore, to be common with the deformation of compacted sandy soil previously used. A method for predicting the converged strain for soil specimens under repeated loading is proposed making use of this simplified law. Since the converged strain by an extrapolation is particularly governed by the load increment ratio and the frequency of repeated loading, the diagram relating the converged strain to the load increment ratio as a parameter of frequency is suggested to be most practically useful in the prediction of settlement induced by repeated loading.

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The purpose of the present study is to explain the shear behaviors of soils under threedimensional stress condition uniquely, by extending the concept of the Spatial Mobilized Plane (SMP) proposed previously. From the reconsideration of the former stress-strain model based on the SMP, new amounts of strain increments (dε_SMP^* and dγ<SMP>^*) which represent the normal and parallel components of the principal strain increment vector to the SMP are defined. Then, a new stress-strain model under shear is proposed on the basis of the idea that there exist unique relations among these new amounts of strain increments and the shear-normal stress ratio on the SMP. The validities of this stress-strain model and the failure criterion based on the SMP are confirmed using the results of the triaxial compression, triaxial extension and true triaxial tests on sand and clay. All the soil parameters of this stress-strain model can be easily determined using the conventional triaxial compression tests.

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Although the degrees of time-dependency in soil behavior somewhat differs between sand and clay, every soil expresses viscoelastic, viscoelastoplastic and creep failure characteristics according to the level of applied deviatoric stress. In this study, the fundamental stress-strain-time relationships of soil skeletons including sand and clay caused by the deviatoric stress are theoretically formulated for various stress levels and are simulated by a mechanical model. In the formulation, originations and functions of the elementary properties of the skeletons such as elasticity, elastoplasticity and viscosity are studied from the microscopic point of view. Then applying these fundamental stress-strain-time relationships to the analyses of the creep behaviors, the author presented not only the various relationships previously proposed by some researchers but also obtained some new relationships.

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The development of lateral pressures at rest in expansive soil are studied under various surcharge intensities with and without interposing cohesive nonswelling soil layer. The surcharge intensities selected for study ranged within and beyond the magnitude of swelling pressure at 'no volume change'. Studies indicated that both cohesive nonswelling soil layer as well as surcharge are significantly effective in altering the lateral pressure and vertical movement of the underlying expansive soil mass. The equations for lateral pressures generated beyond swelling pressure range are formulated.Further, the studies conducted with cohesive nonswelling soil layer of varying shear strengths indicated that its shear strength plays an important role in altering the generated lateral pressures.

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A dike for a reclaimed land was constructed on a highly plastic marine clay. Immediately after completion, it failed and sunk into the sea. Both field and laboratory tests were conducted in order to obtain the undrained strength of the clay and the actual failure plane. Undrained strength for the stability analysis was determined by 1) unconfined compression test, 2) in-situ vane test, 3) the modified Bjerrum's method and 4) the SHANSEP method. Both strength anisotropy and the strain rate effect were considered for the strength obtained from the modified Bjerrum's method and the SHANSEP method, while only the strain rate effect was considered for the in-situ vane strength. Results of stability analysis are summarized below : -1) Factors of safety obtained using the strength values from the modified Bjerrum's method showed good agreement with the field behaviour of the dike.2) Factors of safety obtained using the strength values from unconfined compression and in-situ vane tests were slightly unconservative.3) Factors of safety obtained using the strength values from the SHANSEP method were conservative.

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A stress-strain model for granular materials is proposed by consideration of the mechanism of fabric change under shear. A new relationship between strains and fabric change of granular materials is derived from paying attention to "two particles" across the potential sliding plane and considering the mechanism of disappearance and generation of interparticle contacts with the third particle. Combining the above mentioned relationship between strains and fabric change with that between stresses and fabric change which has been proposed by Matsuoka (1974 a), a stress-strain relationship is formulated under two-dimensional stress conditions. The concept of "Spatial Mobilized Plane (SMP)" is then introduced to extend the stress-strain relationship to that in the three-dimensional state. For example, the stress-strain behaviours under cyclic loading and the liquefaction phenomena are analyzed by the proposed model.

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An extensive soil testing program was conducted on clay and sand materials using three different devices, namely the standard triaxial, the N.G.I. simple shear device and the thin long hollow cylinder. Both monotonic and cycling loadings were used and led to results that dramatize the influence of the boundary conditions present in each device. The use of the simple shear test to simulate the conditions that prevail during landslides or earthquakes is found to lead to erroneous results when compared to the thin hollow cylinder. For both static and dynamic tests the triaxial tests is definitely an improvement over the simple shear one. The thin hollow cylinder is shown to be the most desirable configuration to be used in the soils laboratory for studies related to strength and stability under both static and earthquake situations.

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Laboratory vane tests were conducted on two cohesive soils with plasticity index of 50 and 20. Pore pressure measurements were attempted during the insertion and rotation of the vane by two small transducers embedded in samples and one transducer connected to porous tips at the vane blades. The embedded probes produced satisfactory results, whereas the measurement by the porous tips was not very successful.It was found that high pore pressures were developed by the insertion of the vane and that the subsequent dissipation was completed in about four hours. The pore pressure change during the vane rotation was unexpectedly small. It was confirmed that the time elapsed between the vane insertion and the start of rotation was a very important controlling factor of vane strength. The ratio of the shear strength to the vertical consolidation pressure for long elapsed time increased by about 20% and 45% for soil with plasticity index of 50 and 20 respectively in comparison with the ratio for short elapsed time. The ratio for long elapsed time was slightly smaller than that observed in the vane tests free from the disturbance due to the insertion of the vane. The ratio free from the disturbance agreed fairly well with that obtained with K₀ consolidated and undrained triaxial tests. The rate of increase of the ratio with the plasticity index for short elapsed time compared well with that obtained by Skempton for the vane test.

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The upper bound technique of limit analysis of perfect plasticity is applied to evaluate the stability of slopes induced by earthquake load. The analysis considers the following three cases : (1) homogeneous and isotropic slope, (2) homogeneous but anisotropic slope, and (3) nonhomogeneous and anisotropic slope.The computer models developed are based on the following conditions : (1) Plane strain, (2) plane and log-spiral failure surfaces, (3) pseudo-static earthquake loading, (4) uniform horizontal distribution of lateral acceleration, and (5) Coulomb criterion for failure with variable c but constant φ.

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Three case studies for short term stability problem for the structures constructed on normally consolidated clays at and near failure are described in detail including discussions of the shear strength of soft clays determined by various methods currently practiced.Undrained strength to be used for stability analysis is briefly summarized and the shear strength determined by various methods are discussed as well as considerations on reliability of stability analyses. It is shown that 1) shear strength of soft clay deposits determined by the methods currently practiced is uncertain and 2) results of stability analyses evaluated using such uncertain strength values are unreliable.Results of stability analyses for the three structures constructed on normally consolidated clays at and near failure are described in detail as well as the undrained strength characteristics of the clays at the three sites. Stability analyses were carried out using the strength values from 1) the modified Bjerrum's method, 2) the SHANSEP method, 3) in-situ vane test, 4) unoconfined compression test and 5) Bjerrum's stability chart. Factors of safety obtained from each of the methods are considerably different from each other and strongly demonstrated the importance to recognize the regional variations in evaluating the proper soil behaviour.

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For an earth dam located in a narrow canyon, canyon restraint has significant influence on seismic stability of the dam. A numerical method is proposed for slope stability analysis of three dimensional earth dams subjected to horizontal seismic loading. The method is an extension of the simplified Bishop method, taking into account indeterminate shear force acting between vertical slices transverse to the dam axis. Due to the interslice shear force, limit equilibrium can be achieved at all points on a sliding surface. An iterative calculation procedure is presented to determine the magnitude of the interslice shear force and a critical seismic coefficient of the entire dam. Stability analysis by the proposed method is conducted for small-scale earth dam models used in failure experiments, and the analytical results are compared with the observations regarding the seismic coefficient and shape of failure surfaces. The comparison shows a fairly good agreement, demonstrating validity of the method and providing several useful findings concerning the slope stability.

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A unified theory of the coupled phenomenon of seepage and motion is developed for saturated porous media based on the continuum theory of conservation laws of mass and linear momentum. The phenomenon is typically known as consolidation for static problem.As observed in the Biot's procedure, the usual approach is to add some terms of coupling to differential equations. However this way induces slight difficulties to evaluate physical meanings and coefficients of each term. In order to avoid these ambiguities, the authors begin by constructing conservation laws for saturated porous media, that is, the mass and the linear momentum conservation laws are introduced. The former law is reduced to a coupled seepage equation assuming the averaged velocity concept and the Darcy's law, and the latter to a coupled equation of motion. Under proper constitutive assumptions, the coupled equations may be solved for both static and dynamic problems.

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