Due to embankment construction on soft clay ground, settlement and lateral flow of the foundation ground will occur because of the embankment load. This causes problems not only regarding the stability of the embankment itself but also for the surrounding ground and structures, especially foundation piles. If the extent and amount of lateral flow can be predicted prior to construction, soil improvement of the existing ground to prevent this lateral flow is possible. In the present investigation, field observations were made at 11 sites in the undrained states immediately after embankment construction. From the investigations, it was found that the following pairs of quantities are closely related to each other : (i) the maximum underground lateral displacement and settlement of the embankment, (ii) the maximum underground lateral displacement and horizontal displacement of the ground surface, (iii) the depth of the maximum underground lateral displacement at the embankment toe and the embankment width, (iv) the maximum underground lateral displacement under the embankment toe and the embankment load, (v) the maximum underground lateral displacement depth under the embankment toe and distributions both of underground vertical stress of the embankment load and the soil properties of the foundation ground. These have been synthesized to form a practical procedure of predicting the magnitude and extent of lateral flow of the clay foundation under an embankment.

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A constitutive model for soils subjected to monotonic and cyclic loading under general stress conditions is presented which has neither an elastic domain nor a yield condition. Two formulations are built in the model according to the sign (plus or minus) of the linear combination of the first and second invariants of the viscoplastic strain rate tensor. In each formulation, a new stress-ratio parameter η^# is introduced, and the linear combination of these accumulated strain invariants is related to a function of effective stresses and time. Constitutive relations are derived by using the concept of potential theory, with the help of an elasto-viscoplastic model called the Sekiguchi-Ohta model. The model presented here agrees with the Sekiguchi-Ohta model in a special case, and with the original Cam clay model in a more special case. The model can describe anisotropic responses due to initial stress anisotropy, initial structural anisotropy and loading reversal, rate effect, phase transformation, etc. The results of the simulations for several typical triaxial tests qualitatively indicate the applicability of the model to a wide extent of loading conditions.

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From microscopic point of view, consolidation of clays takes place when the driving forces for pore water flow exceed the forces tending to hold the water to clay particles. To consolidate soft clays, theoretically two ways can be considered. One is to enhance the driving forces for pore water flow and the other is to reduce temporarily the forces tending to hold the water. While conventional methods for consolidation are based on the former way, this paper deals with the latter idea by making use of electro-chemical properties of clay soils. In order to reduce the forces tending to hold pore water, an electrical disturbance was imposed to clays by loading alternating electric current (AC). A series of consolidation tests of marine clays under AC field were carried out. It is found that the consolidation of clays can take place by the loading of AC whose magnitude is larger than a critical value. In AC consolidation, the initial swelling and the subsequent consolidation was observed. The initial volume increase is considered to be an unique characteristic of the AC consolidation.

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The aim of the present paper is to analyse the mechanical behaviour of a steep slope reinforced with nails, using continuum mechanics approach. First, a short description of the nailed structure and a method of nailing are presented. Then, a continuum elastic theory of reinforced soil is applied to predict stresses in the reinforcement. The soil is assumed to be uniformly reinforced in the nails direction. The soil and the reinforcement are assumed to work together, i. e. slippage on the interfaces between both constituents is neglected. It is also assumed that both constituents coexist at every point of the material, so the reinforced soil can be treated as a macroscopically homogeneous material which is transversally isotropic. The macroscopic behaviour of reinforced soil is described by the mechanical properties of constituents, their partial fractions and geometrical arrangement. Respective formulas are presented and then the boundary value problem formulated and solved with the help of finite element method, for the data corresponding to the real field problem. The theoretical predictions are compared with experimental data obtained from the field measurements on a full scale slope reinforced with nails. A brief description of the limit plasticity approach to the problem of bearing capacity of reinforced soil structures is presented and its application to the analysis of field measurements described. Again, the theoretical predictions are compared with experimental data. It seems, that in both cases, a reasonably good agreement between theory and experiment has been obtained.

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Responding to the increasing need for determining the strength and deformation characteristics of gravels in situ, an improved method of sampling by in situ freezing to obtain a high quality undisturbed sample of saturated gravel from a depth of about 20 m below the ground surface was developed. Two different types of undrained cyclic triaxial test for determination of liquefaction strength and deformation characteristics were conducted on the undisturbed deluvial gravel samples after they had been thawed. For studying the effects of sample disturbance, undrained cyclic triaxial test were also conducted on the reconstituted specimens. Based on the above studies it was shown that (1) three new developments in the technique of sampling by in situ freezing on gravel were successfully achieved in the field, (2) the shear modulus of undisturbed samples at minute strain level matches the value calculated from shear wave velocity, which assures a high quality of samples taken by this method, (3) the shear modulus of undisturbed samples is approximately 30% greater than that of reconstituted samples, and (4) the liquefaction resistance of the reconstituted samples is only about 50% of the value of undisturbed samples, even though they have the same density.

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A series of undrained triaxial stress relaxation tests on four saturated remoulded clays consolidated under isotropic stress condition were performed to investigate the influence of imposed strain level and strain rate prior to the start of relaxation test on the principal stress difference and pore pressure versus elapsed time relationships. Experimental results show that the principal stress difference versus logarithm of time relationship is approximated by the two straight lines independent of strain level, strain rate and mode of stress application in the preceding undrained shear process, and that the stress state corresponding to the point of intersection of the two straight lines locates close to the effective stress path calculated by the Cam-clay model proposed by Roscoe et al. (1963). A sign that the principal stress difference finally approaches to a limiting equilibrium value is found from the test results. It is also shown that the stress points corresponding to the equilibrium state lie below the Cam-clay effective stress path and the curve linking these stress points makes a similar shape of the path. The slope of the initial straight line on the principal stress difference versus logarithm of time plot depends on the magnitude of strain imposed in the preceding undrained shear process. Plastic component of the change of pore water pressure, which was defined by Lo (1969), during stress relaxation test depends not only on the strain level but also on the strain rate prior to the test.

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As shown by de Beer, the bearing capacity factor N_γ decreases with increasing foundation width. It is demonstrated that this scale effect can largely be attributed to the influence of pressure level on the friction angle φ. By means of improved triaxial tests with large samples, an empirical relation is proposed among the angle of friction, φ, and the pressure level, for different sands. Below a threshold value, φ is pressure independent ; a power law is adopted above this value. An empirical formula for the dependence of N_γ on φ is proposed. The calculation procedure is based on a proposal by Meyerhof. The mean foundation pressure is approximately proportional to the pressure level in shear tests giving the mean value of the friction angle in the calculation of N_γ. The proposal is examined by published results of numerous foundation tests at small and at large scale. These tests were performed at 1g gravity and at ng in the centrifuge. A detailed analysis of progressive failure is largely circumvented, as justified from the evidence of the presently available experimental data.

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Aiming at estimating K₀-value (the coefficient of earth pressure at rest) of a saturated medium dense sand, a series of anisotropic consolidation tests (σ'₃/σ'₁=constant) and K₀-consolidation tests (ε₃ =0) were carried out. Toyoura Sand, the relative density of which is about 70%, was used in the experiments. In the anisotropic consolidation tests, it was shown that the principal strain ratio (ε₃/ε₁) converges to some values in response to the increase of stress level. Then the K₀-values were interpolately (or extrapolately) determined as a principal stress ratio corresponding to zero principal strain ratio based on the relationships between the principal stress ratio and the principal strain ratio. The K₀-values estimated from the anisotropic consolidation tests and the K₀-consolidation tests were O.61 and O.58 respectively and were found to be about 50% higher than the values estimated from Jaky's equation. In the experiments of this investigation, the influences of the volume change due to membrane penetration or compression of filter paper, the end friction, the reference state etc. on the experimental results were carefully investigated. It was made clear that the obtained K₀-values were largely affected by the volume change correction.

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A slurry deposition method of preparing homogeneous samples of well graded and silty sands is described. The method yields homogeneous saturated samples that are easy to replicate and possess fabric similar to that of natural fluvial sands. Since water pluviation results in segregation of well graded and silty sand, the proposed technique provides a convenient method of fundamental study of undrained behaviour of these liquefaction prone materials.

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Many of the simple shear devices which have been used to study soil behaviour under cyclic loading do not provide sufficient measurements to determine the complete stress state of samples of soils tested in them. Consequently, certain assumptions regarding failure are normally made in interpreting the results. Tests on a dry sand under constant vertical loads were conducted in the elaborately instrumented Cambridge University's cyclic simple shear apparatus and the results of the stresses on the center of the samples are presented. The results revealed that failure in simple shear strain is initiated on the vertical planes at a very early stage of the tests. But, neither the vertical nor the horizontal planes are planes of maximum stress obliquity. The planes of maximum stress obliquity are inclined at (π/4-φ/2±ψ) to the horizontal of planes on which the maximum shear stress ratio occurs where φ is the angle of internal friction and ψ is the inclination of the principal axes of stress to the vertical planes. At low levels of shear strains the inclination of the principal axes of stress and of strain increments were, in general, non coaxial.

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The effect of sediment-filled valley on seismic ground motion has become of major interest recently. In this paper the boundary element method (BEM) is used for the response analyses of axisymmetric valleys subjected to incident waves, and the vibration characteristics of the valleys are investigated in detail. The errors resulting from using the full-space fundamental solutions and the finite model simulation are theoretically clarified. The axisymmetric problems are solved by considering the cyclic symmetry of the coefficient matrix and introducing a transformation. The case studies are performed for examining the effects of the shape ratio, the impedance contrast, the oblique incidence of body waves, the Rayleigh wave incidence and the valley damping on the resonance characteristics. The main conclusions are as follows. The specific resonance patterns of valleys exhibit two modes, namely the shear modes and bulk modes. The frequency of resonance modes is shown to depend only on two parameters : the one-dimensional resonance frequency at the valley center and the shape ratio, regardless of the incident wave field and impedance contrast. The fundamental resonance amplitudes depend on the shape ratio and the impedance contrast. The proposed empirical formulas for estimating the fundamental resonance frequencies and the maximum fundamental resonance amplitudes at the valley center are verified by numerical examples for valleys with different shapes and extensive impedance contrast.

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This paper aims to extend the first author's method for simulating the time dependent stress-strain behavior of isotropically consolidated clays, taking into account the various time effects in the anisotropically K₀-consolidated clays. The fundamental postulate in the method is that the stresses and strains in soils behave themselves in a way of minimizing the whole dissipated energy within the limitations required by several constraints, i. e. the equations of equilibrium, the experimental relationship between the stresses and volume change, and so on. By the use of an additional assumption concerning the time dependency of dilatancy, the method provides a unified representation of various time effects such as the constant strain rate shear, stress relaxation and creep processes. In order to extend the method to the shear of the K₀-consolidated clays, this paper adopts some new devices, for instance, the plotting system of stress trajectory which enables to apply the energy equation in the original Cam Clay model to the extension tests without any modification. Such devices may lead to disclose the mechanical framework of the existing constitutive models. Based on these devices it is shown that the proposed method can appropriately describe a wide variety of time effects both in the triaxial compression and extension tests of K₀-consolidated clays. The stress-strain response predicted by the method shows a fairly good agreement with the measured results. Through the development and application of the method, many important properties in the undrained shear of K₀-consolidated clays are clarified from the physical viewpoint.

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A rigorous solution for the consolidation of soil by displacement-type vertical drains with finite permeability is presented taking into account the disturbance in a clay ring surrounding the drain pile caused by drain installation. The accuracy of both Barron's and Hansbo's approximate solutions regarding well resistance and smear is examined in detail by comparing with this rigorous solution. The numerical results reveal that the influence of the disturbance upon the consolidation rate is notably large for the type of soil whose permeability decreases with the disturbance. In this case, existing approximate solutions are shown to be sufficiently accurate for practical application. For the type of soil whose compressibility increases with the disturbance, on the other hand, the influence of disturbance is relatively small. For both soil types, simple equations are proposed to obtain an equivalent "ideal" well having an increased spacing ratio on the basis of analytical results derived from the rigorous solution.

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