Laboratory model test results for the ultimate bearing capacity of two closely-spaced strip foundations on sand have been presented. The model test results have been compared with the theoretical study given by Stuart (1962). The nature of variation of the experimental efficiency factors, α_q and α_r, associated with the bearing capacity factors, N_q and N_r, are similar to those predicted by the theory; however, their magnitudes are substantially lower for S/B<about 3. The foundation settlement at ultimate failure load increases for S/B<4.5 when compared with that of an isolated foundation.

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The objective of this study is to provide a simple yet accurate procedure for the probabilistic stability analysis of an embankment constructed on a soft clay with finite thickness. The analysis is based on the conventional φ_u=0 and circular arc slip surface assumptions.The probabilistic soil profile description with respect to the undrained shear strength within a clay deposit is given first introducing a simple stochastic process. This is shown to be a general expression for the spatial variation of the strength of clays including the conventional deterministic soil profile as a special case. The probabilistic description of the soil profile is, however, transformed into the set of eight different deterministic soil profiles, each of which is a three-layered system with three different strengthes. Through the composition of these multi-layered systems, it is demonstrated that all the possibility in the distribution of a factor of safety can be covered by only eight times of execution of the deterministic, and then, conventional slope stability analysis for eight deterministic soil profiles. From this, the layered system is called in this study an equivalent multi-layered system.The developed procedure is illustrated in the case studies including a multi-failure mode problem, from which the simplicity as well as the accuracy of the proposed method is verified for the use in practical design.

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Using the so-called pseudo-static method, a stability analysis was made for the mountain slide that took place at Mitake-iriya village at the time of the Izu-Ohshima-Kinkai earthquake of January 14, 1978. Undisturbed samples of volcanic clay were obtained in blocks from the exposed surface of the deposit identified to have been the sliding surface. The partially saturated clay samples were tested under consolidated undrained conditions using the triaxial test equipment. Dynamic axial stresses with irregular time histories were applied to the specimens in combination with statically sustained axial stresses to determine the soil strength under the conditions simulating in-situ states of stress during the earthquake. The results of the tests were expressed in terms of the Mohr-Coulomb type failure criterion which showed that, while the angle of internal friction remained almost unchanged, the cohesion component in irregular loading increased above values obtained in the static loading. Using the strength parameters thus determined, a pseudo-static analysis was made to check the stability of the soil masses that had actually slid during the 1978 earthquake. The maximum horizontal acceleration required to cause the slide was computed. The computed accelerations were shown to cover a range between 400 and 500 gals which is consistent with the range estimated by other investigators on the basis of overturning of tombstones in the vicinity of the slide area.

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The physical, chemical, and mineralogical properties of the clay sediment in Ariake Bay area were examined, and the relationships of the consistency limits of the clays to their physical and chemical properties were investigated by statistical methods. The consistency limits were found to be significantly correlated with the clay content, specific surface area, and cation exchange capacity by simple regression analyses. Multiple regression analyses indicated that the clay content and salt concentration in the pore water were the most significant variables explaining the variation of the consistency limits. It was also found that the salt concentration in the pore water was correlated with the activity of the clays, and that the upper clay layers having greater activity contained the higher amount of salt in the pore water.

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The influence of static shear on undrained cyclic loading behaviour of Ottawa sand has been studied using triaxial samples anisotropically consolidated to various stress ratios. It is shown that the presence of static shear does not always lead to increased resistance to liquefaction or cyclic strain development. The resistance to liquefaction can increase or decrease with increasing static shear depending on the relative density, magnitude of the static shear and the specified level of strain development. It is alos shown that flow deformation occurs during cyclic loading of loose sand much in the same manner as observed by Castro in monotonic tests, and is responsible for sudden strain development during cyclic loading.

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In order to study the deformation and liquefaction characteristics of sand subjected to cyclic stresses involving changes not only in magnitude but also in direction, several series of static cyclic tests were performed on cubical saturated sand specimens in undrained conditions using a true triaxial test apparatus. The octahedral plane in the three-dimensional stress space was envisaged as representing the horizontal plane in the in-situ sand deposit, and three principal stresses were cyclically applied to the specimens so that circular, elliptic and crisscrossing stress paths could be produced in the octahedral stress plane. The analysis of stress and strain increment vectors on the octahedral plane showed that the sand manifests the deformation characteristics like an elastic body at the beginning of cyclic loading where the developed pore water pressure is still small, but at the end of the cyclic loading near the incidence of liquefaction the sand tends to behave more like a perfectly-plastic body. The results of the tests also indicated that the resistance to liquefaction became smaller as the stress paths changed from the straight-line to the ellipse and further to the circle.

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The influence of strain rates on pore pressures of cohesive solis in consolidated-undrained triaxial tests was experimentally studied. Three types of cohesive soils were used; Kawasaki clay with plasticity index of 30 and two artificial mixtures of Kawasaki clay and Toyoura sand with plasticity index of 20 and 10. Pore pressure measurements were carried out by small transducers at the centre, bottom and periphery of triaxial specimens. It was found that at low strains the pore pressure at the centre was larger than that at the bottom and periphery, while at high strains the difference was less significant. The difference in pore pressures at the three different locations was smaller for lower strain rates and for soils with lower plasticity index. Pore pressures in undrained triaxial specimens of soil with plasticity index up to 30 were considered to be uniform at the strain rate of 4%/h. It was concluded that the test duration given by Blight was satisfactory from the standpoint of pore pressure equalization.

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In order to investigate the undrained shear strength anisotropy of cohesive soils of intermediate grading between sands and clays, a series of consolidated undrained triaxial compression and extension tests is performed on soil samples which are prepared by mixing Kawasaki clay and Toyoura sand (with crushed fraction) so as to obtain a wide range of soil type expressed in terms of plasticity index I_p. Four kinds of cohesive soil samples with I_p of 30, 20, 15 and 10 are tested.The conclusions from this study are : 1) Undrained shear strength anisotropy increases with decrease in I_p. And difference between values of (c_u/P)E/(c_u/P)C obtained by (CIU)^^^- and (CK₀U)^^^- tests increases as the plasticity index increases.2) Relationship between c_u/P values obtained by four types of consolidated undrained triaxial tests and I_p is quantitatively shown.3) In view of either shape of effective stress paths and the undrained shear strength anisotropy, shear properties of cohesive soils of I_p of 20 and 30 are seen to be those of clays, however, soils of I_p of 15 and 10 are considered the intermediate soils.Based on results of the present study, a way of accounting for the anisotropic undrained shear strength in stability analysis is proposed, with assumption that the in situ undrained compression strength of vertical sample is known.

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Stress controlled cyclic triaxial tests, under undrained conditions, performed on sand samples consolidated under a range of different principal stress ratios (chosen to reflect and simulate the in-situ stress conditions) affect greatly the generation of pore pressures with the increasing number of cycles of repeated loading.In the following an attempt is made to bring a theoretical interpretation of these experimental observations regarding the tendency of lesser volume changes leading to smaller pore water pressure increases in anisotropically consolidated triaxial sand specimens under dynamic loads.

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A numerical procedure consisting of a combination of the finite element method and the mathematical programming, is proposed for estimating material constants of soil deposit based on field measurements. The procedure allows to correct the unknown material constants in a way that the differences between observed and the estimated values decrease sufficiently. Some examples of estimating elastic constants are also presented.

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A linear elastic finite element analysis was made to investigate the magnitude of the stresses generated in short circular cylinders subjected to axial displacement with rigid end platens and lateral stress; no slippage being allowed between the specimens and the platens. Four Poisson ratios and various height to diameter ratios are examined. The stress distribution is shown to be highly nonuniform and strongly dependent on Poisson's ratio. The results are significant in view of the extensive use that is made today of various simple shear devices.

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