The purpose of this paper is to evaluate the relation between initial shear modulus and shear strength of cohesive soils. The initial shear moduli were obtained from the results of the well-shooting tests by means of shear waves, while the shear strength could be obtained from the results of laboratory tests conducted on undisturbed soil samples collected at the same site as the well-shooting tests. Taking into consideration the fact that there have been a number of instances where the well-shooting test and the standard penetration test were conducted on the same sites, the authors conducted their research to seek some relationships between the initial shear modulus and the N-value of the standard penetration test, between the shear strength and the N-value, and between the initial shear modulus and the shear strength. The research works have finally led the authors to finding out several relations among initial shear modulus, shear strength and N-value.

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The formulas of the relationship between stress ratios and strains due to dilatancy derived from the microscopic analysis based on observation of the particulate nature of soil (Matsuoka, 1973; Matsuoka, 1974) have been verified with respect to the measured data of drained triaxial compression and extension tests on sand and clay. From the test results, it is judged that dilatancy of soil may be governed uniquely by the shear-normal stress ratio (τ/σ_N) on the mobilized planes or the principal stress ratios (σ₁/σ₃, σ₁/σ₂, σ₂/σ₃) as indicated by the above formulas. This concept differs from the view advocated by Shibata, Karube et al. (1963, 1964, 1965) that the volumetric strain caused by dilatancy is governed by the principal stress difference vs. mean effective principal stress ratio ((σ₁-σ₃)/σ_m≡q/p). Further, it has been demonstrated that the stress-strain relationship in drained triaxial compression tests under a constant lateral pressure (σ₃) and the stress path in undrained triaxial tests can be calculated by assuming the superposition of the above-mentioned strains due to dilatancy and the strains due to consolidation. Thus, it is inferred that dilatancy of soil as well as shear resistance (strength) may obey Coulomb's law of friction.

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Some results of research on the strength of dry sand are presented, based on experiments carried out over a period of several years on the geotechnical properties of dry sand subjected to repeated loading. The dependency of the dynamic strength of sand on the number of cyclic loading, static stress state of sand prior to the application of cyclic stress, initial and at failure void ratios of the sand, etc., were investigated, and comparisons were also made between the dynamic strength and the static strength. The test results indicate that dry sand shows a higher strength against dynamic load than that against static load, but in view of deformation, sand is less stable against repeated loading.

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In the theory of coastal ground water in shallow strata the shore line, the contact line of the sea and the land surfaces, is usually assumed to be stationary. However, when a sea beach is sloped, the shore line moves to and fro according to the rise and fall of the tide. In this paper, the authors present a theory including the effect of the moving boundary on the coastal ground water tide which is often encountered in the lowland along the Japanese coast. It is proved by this theory that the effect of the moving boundary due to the sea tide is found in the amplification of the fundamental oscillation of coastal ground water and in the occurence of third harmonic in ground water tide.This theory explains the particular ground water tide of the Miho Peninsula, a sand spit protruding into Suruga Bay, on the Pacific coast of Japan.

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A series of cyclic triaxial tests with varying amplitude was performed on samples of a sand in which they were subjected to stress reversal from compression to extension and vice versa. In the first place, the effect which the previous stress history in triaxial extension may have on the current deformation characteristics in triaxial compression, and vice versa was investigated. It was found that yielding of sand in reversing stress condition could occur independent of the previous stress history in an opposite direction, as long as the stress amplitude was made to stay within some limit. On the basis of the dircetional independency as above, together with the knowledge concerning the deformation characteristics under monotonous loads, an attempt was made of assessing how dilatancy and shear strains develop progressively during cyclic loading. This method proved to be applicable not only for stress-controlled but also for strain-controlled performance of sand.

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A numerical integration procedure is used to evaluate the equations which give the initial distribution of excess pore water pressure in a subsoil due to a trapezoidal surface load, such as a highway embankment, and a series of curves are provided for a broad range of geometrical variations. Although the foundation soil is assumed to be saturated, the effect of soil dilatancy is taken into account. The resulting information on pore pressure distributions can be conveniently employed in conjunction with classical consolidation theory to determine the ultimate consolidation settlements which occur under the applied load.

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