Effects of irregular series of earthquake-induced cyclic stresses and the K₀-value at the time of consolidation on the liquefaction resistance of sand are discussed by examining the results of several series of cyclic triaxial tests that have been performed at the University of Tokyo. Relationships are established in a graphical form between the applied shear stress and the residual pore water pressure, that is, the pore water pressure which remains after through application of irregular time histories of shear stress. On the basis of these relationships, with the effects of irregularity of wave form and the K₀-value being incorporated, a practical method is proposed to evaluate pore water pressures as well as factor of safety against liquefaction that can develop in a horizontal deposit during an earthquake. The method is applied to analyze the liquefaction of a sand deposit in Niigata where a detailed investigation was recently carried out for cyclic strength of undisturbed samples.

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Resonant-column tests were performed intending to clarify the effects of grain size distribution on shear moduli of normally consolidated disturbed sands for shear strain ranging from 10^-6 to 10^-4. The sands tested are clean sands which are uniform and do not contain fine particles, natural sands which are not uniform and contain fine particles and other artificially graded sands. The test results indicate the followings. Shear moduli of the clean sands tested at strain levels of γ=10^-6, 10^-5 and 10^-4 are expressed approximately by the similar empirical equations irrespectively of grain shape and grain size. For the sands other than clean sands, however, shear moduli decrease with the increase in uniformity coefficient and also decrease with the increase in the content of fine particles. Therefore it is concluded that in estimating shear moduli of ordinary natural sands which are not so uniform and contain fine particles, it is preferable to conduct resonant-column tests on the sands of interest. When tests are not conducted, the effects of grain size distribution on shear moduli should be taken into account.

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The construction control of the structures has been recently recognized as one of the most important matters in a series of design procedures. An embankment on a soft ground is usually constructed by the smaller safety factor compared to other structures, because the change of design under construction is comparatively easy in the earth work. This makes it especially important in the embankment construction to control safely and quickly by using the information obtained from the practically possible measurements. The present paper describes the study on the method in which the degree of safety at the present situation is ascertained and the successive failure is predicted by observing the vertical settlement at the central place just under an embankment and the horizontal displacement near the toe of the slope. Many observed and numerical examples are shown, and on the basis of them, the diagram for practical use of the construction control is proposed.

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The probability model of the undrained strength of saturated clay which can correctly represent the heterogeneity is indispensable for the reliability-based design of a soft ground. In the present study, the theoretical model specification is firstly shown. The variability of undrained strength is analyzed quantitatively from two points view, which is the new idea of modeling the strength. That is, one aspect is concerned with the variability due to sample disturbance which is inevitable at sampling and testing of soils. The other is the inherent heterogeneity of a natural ground. Speaking of the sample disturbance, the ratio of strength of a disturbed sample to that of a perfect one is formulated by a probabilistic function of the disturbance ratio. On the other hand, the inherent variability of undrained strength is analyzed based on the perturbation of consolidation pressure due to heterogeneity of a ground. The final probability model of measured undrained strength is obtained by convolution of those two kinds of variability.It is secondly showed that all of the theoretical inference obtained from the above stated consideration is supported by statistical model identification of using a large amount of actual data.

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Rapid stage construction of homogeneous and isotropic embankments is examined. The finite element model constructed assumes an undrained, linearly elastic-perfectly plastic behaviour of the soil. The von-Mises criterion is used to identify when the shear strength is exceeded. The plastic range analysis is based on Yamada et al.'s formulation of the inversion of the Prandtl-Reuss stress-strain relationships. For every strain increment, corresponding to the loads of a new layer, the stress increments are computed and added to the existing stresses. The new stress level defines the new stiffness matrix to be used in the subsequent loading. Numerical examples are solved using this process, which was coded in the computer program FEMDAM, and the expansion of the plastic zone is presented. The boundaries of the plastic zone may also constitute boundaries for a possible slip surface.

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Laboratory pullout test results on rough rigid model piles in dry sand are presented. Tests were conducted for various pile embedment ratios in loose, medium, and dense sands. Test results show that, for short piles, the average uplift skin friction, f^^-, may be approximated to increase linearly with the embedment ratio, L/D. The experimental average uplift skin frictions have been compared with the theory presented by Meyerhof (1973) which is of the form, f^^-=1/2 K_uγL tan δ. The comparison shows that, while using the above theoretical uplift coefficient, K_u, a careful estimate of the soil-pile interface friction angle, δ, is necessary. The ratio of δ to the soil friction angle, φ, varies from about 0.4 for very loose sands to about one in dense sands with relative density greater than 70 per cent.

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