Safety factors of embankments are analyzed in relation to the variabilities and the uncertainties of soil properties. It is concoluded that the unconfined compression strength of a saturated homogeneous clay layer and the strength parameters c_u and tanφ_u of an unsaturated homogeneous silty soil layer follow the theoretical normal distributions. Such physical properties as moisture content and moist density of those soil layers and moist density of an embankment just after construction are also shown to be taken as the normal random variables. A new design factor is defined and the relation between the design factor and the probability of sliding fuilure of an embankment is formulated under consideration of the randomness of the soil properties. Numerical and practical examples show that the embankment with an ordinary value of the design factor (F^^-_s^*=1.1∼1.5) has an unexpected high value of the probability of sliding failure as 15%∼20%.

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In order to analyse the time-dependence of the stress-strain behavior of saturated clays, a nonlinear theory with the single integral representation has been proposed and compared with the experimental results. It is revealed that the relative deformation-dependent response function in the theory can be reduced to a simple form easy to treat by introducing the relaxation spectra and making use of stress relaxation characteristics. Thus, it is shown that the proposed theory successfully predicts several time-dependent behaviors such as stress relaxation after the stoppage of steady shear, steady shearing and steady state creep. Furthermore, the equilibrium properties are discussed in relation to consolidation and dilatancy characteristics.

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The present study has theoretically treated the consolidation process by the vertical drain method, taking the well registance into consideration. Rigorous solutions of this problem have been given in graph forms and will be of great use in the analysis of the stabilization of soft soils by means of drain wells. The derived quantitative data predict that the effect of well registance should be taken into account for the design of vertical drains in the case of deep and soft deposit which is often found in Japan.

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Based on stress-strain elationships on the mobilized plane, general stress-strain relationships of soils under three different principal stresses were formulated by introducing a new concept of three compounded mobilized planes. The formulas of these stress-strain relationships were verified with respect to measured data of triaxial compression tests, triaxial extension tests, plane strain tests and true triaxial tests on sands and glass beads.

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By employing different kinds of stress paths drained triaxial compression tests were conducted on sand samples having several densities. In the course of complicated cycles of stress change, the states of stress at which plastic deformations begin to take place were determined. Simple analysis using a number of plastic yield points thus obtained permitted families of yield loci to be established in the stress space, depending upon the densities of the sand samples used. The proposed form of yield loci is compared with the similar loci suggested by Schofield and Wroth, and Poorooshasb, and coincidence or difference between these were examined in the light of the results of tests specially performed for this purpose.

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Taking special notice of the similarity of shear characteristics between sands and clays, the author sought to apply to clays the stress-strain relationships which were derived from the microscopic analysis and which were experimentally verified with reference to sands and other granular materials. The stress-strain relationships were verified with respect to measured data of drained triaxial compression tests on various kinds of normally consolidated and overconsolidated clays and the related microscopic mechanism was also considered. It was shown from the test results that the shear phenomena of sands and clays could be analyzed on the basis of the same principle, suggesting that they might occur in a fundamentally similar mechanism.

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The effect of soil modulus, mode of wall movement and base friction conditions, on lateral earth pressure distribution and pattern of failure development in the soil mass is brought out.

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Non-dimensional curves for computation of consolidation settlement of square, rectangular and strip loaded areas in normally consolidated clay deposits of semi-infinite extent have been developed. Two types of stress distribution, viz., Boussinesq and Mindlin, have been used to evaluate their significance. At higher embedments settlement computations with Boussinesq's equation for stress distribution, as expected, are found to be much larger than the settlement computations if Mindlin's equation is used. While the settlement phenomenon beneath a loaded area might continue up to large depths, it has been shown that a major portion of the settlement occurs within a small depth below the loaded area. This makes the design curves reasonably applicable to loaded areas on confined layers also. The usage of the design curves for use in practice has been demonstrated with a numerical example.

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