This paper deals with the shear strength characteristics of saturated, remoulded, montmorillonite and Kaolinite clays as affected by changes in soil structure. The changes in soil structure were made by changes in initial moulding water content, stress history and type of cation and its concentration in the electrolyte system. Throughout the investigation, isotropically consolidated undrained tests with pore water pressure measurements were conducted. The experimental results show a definite cohesion intercept even for saturated normally consolidated clays, under certain conditions. The modified effective stress concept, which takes into consideration the electrical attractive and repulsive forces appears to explain satisfactorily the strength mechanism. The qualitative analysis of the test data brings out the dire need for quantitative evaluation of electrical attractive and repulsive forces in order that a realistic determination of strength parameters could be made. The manifestation of components of shear resistance has also been discussed briefly.

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The problem of finding vertical stresses and displacements at different depths is of common occurence in the design of foundations. In general, for obtaining stresses and displacements at different depths, Newmark's influence charts are used for loaded areas of arbitrary shapes. However, in this approach, the loaded area has to be drawn to different scales for obtaining stresses and displacements at various depths. To overcome this difficulty, a modified approach is presented wherein by drawing the loaded area to a suitable scale, the vertical displacements at different depth can be easily calculated. Both Boussinesq's, as well as Westergaard's solutions are considered. Non-dimensional charts are presented for the normal ranges of values to facilitate computations.

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In order to know a variation of the compressive stress with depth, occurred in a pile driven into soft soil and subjected to negative skin friction due to its subsidence, the equation proposed by H.B.Seed & L.C.Reese was solved under the assumption of an elastoplastic relationship between the relative displacement of a pile to its surrounding soil and its skin friction. On the basis of the solution thus obtained, the general expressions with respect to a location of inflection point, maximum compressive stress, stress at a pile tip, and settlements of the top and the tip of a pile were developed. Futhermore, some shapes of distribution both of initial skin friction due to an acting load and of a soil subsidence were adopted into these expressions to provide with formulae for practical use, and they were diagrammed. A comparison with the values computed by such analytical procedure to the ones measured on the field tests gave to some extent satisfactory agreement.

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Natural clay deposits exhibit nonhomogeneity and anisotropy in shear strength to a considerable degree. In order to take these into account, an analysis is presented herein for the ultimate bearing capacity of strip footings on two-layered purely cohesive soil, wherein the undrained cohesion is anisotropic and varies linearly with depth, in each layer. Values of the bearing capacity factor N_c, are presented for the case of a single layer of clay in which the undrained cohesion decreases linearly with depth in the upper region and thereafter increases linearly with depth, simulating the case of clays subjected to lowering of water table and consequent desiccation.

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A brief explanation of the mathematical representation of state surface and swelling wall is given based on the stress-void ratio relations of clays. The changes of the mechanical state of normally consolidated and overconsolidated clays stressed under various conditions are derived. Combining the concepts of state surface and normality, general incremental stress-plastic strain relations for clays are given. The stress-strain relations for normally consolidated and overconsolidated clays under various conditions are also discussed. The theory can only be applied to the prediction of strains where the void ratio is a unique function of the imposed stresses.

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The authors studied the classification system for coarse soils based on the maximum dry density and the optimum moisture content of the modified AASHO compaction test, the soaked CBR at 95 percent of the maximum dry density, and the coefficient of permeability of compacted soils. After this study, the best boundaries between clean gravels or sands, gravels or sands with some fines, gravels or sands with fines, and fine soils were found to be 5%, 15% and 50%, respectively. And the criteria of well-graded gravels or sands were found to be the coefficient of uniformity C_u greater than 10 and the coefficient of curvature C_z between 1 and √(C_u).Based on these considerations, the authors proposed a modification of the Unified Soil Classification System using the above-mentioned criteria and 2.0 mm for the gravel-sand boundary, and showed the relationships between the engineering properties and the modified classification system for coarse soils.

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A series of shear tests with static cyclic loading for uniform dry sand was carried out to find an effect of strain amplitude on the shear modulus and damping by a simple shear apparatus using a sensitive inclinometer to measure shear strains. The results are compared with the computed results proposed by Hardin and Drnevich (1970) which show a fairly good agreement with respect to the damping and the shear modulus. The simple shear apparatus is simple to operate and can cover a wide range of shear strain.

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