A series of undrained cyclic triaxial compression tests has been performed on a high plasticity marine clay. Testing was performed using various combinations of initial static and subsequent cyclic shear stress on isotropically and anisotropically consolidated specimens. Additionally, monotonic triaxial compression and extension tests were also performed on the same clay with the same initial condition. The cyclic shear strength was considered first, and then, the accumulated shear strain was investigated related to the effective stress ratio at the peak cyclic stress. Based on the experimental results, a semi-empirical model is proposed for evaluating the development of pore pressure and residual shear strain during cyclic loading. The model successfully explains the behaviour of clay subjected to various magnitudes of initial static and subsequent cyclic shear stresses.

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A case study is presented of the application of direct shear and cone penetration tests to soil investigation, design and quality control for an expressway embankment constructed on a peaty subsoil with multi-loading stages. Soil investigation results and various correlations to be used for design and quality control obtained from the two tests are presented. Shear strength and degree of consolidation during construction estimated from the cone penetration test are shown and compared with those evaluated from the settlement measurements at the site. In addition, a detailed stability analysis is made on an embankment which failed during the construction at a height of 6.3 m. The degree of consolidation and results of the stability analysis clearly indicated that the direct shear and the cone penetration tests are effective tools for soil investigation, design and quality control for embankment construction on peaty subsoil profiles.

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The Sand Compaction Pile (SCP) method is considered to be a displacement type pile method, in which a considerable amount of "set-up" of the undrained shear strength of the surrounding clay is anticipated. A simplified procedure for analyzing the set-up problem is presented in two stages. The first stage is the soil-water coupled rigid plastic finite element method which is employed for solving undrained failure of clay due to pile driving, and the other, a linear elastic consolidation computation which accounts for the decrease of void ratio of the clay after pile driving. The value of this simplified method is examined through (1) laboratory set-up experiment on a remoulded Kawasaki clay using a triaxial apparatus aud (2) the case record of in-situ loading test on soft clay improved with the SCP method. In the latter case, extensive improvement in the soft clay was found particularly at a large depth of the soft clay layer, where the set-up ratio was more than two.

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The results of pullout experiments employing one and two reinforcement layers are described. The results imply that the concept of an internal slip surface, passing through all reinforcement layers, may not always be valid. This validity is questioned when reinforcement layers, exhibiting significant stiffness at small strains, are closely spaced. The relevance of this observation to current design practice is also discussed.

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An experimental attempt was made to distinguish between primary and secondary phases of consolidation of soft clays under incremental and continuous loading. The consolidation mechanism of soft clays under elevated temperature conditions was also investigated. Making use of the differences in the replaceability of exchangeable cations absorbed to the clay particles, a special method of preparation of the clay samples was developed. The time-dependent variations of concentrations of the particular types of cations Ca²⁺ and Na⁺ which existed in the pore fluid drained from clay samples during consolidation were obtained from quantitative chemical analyses. The greater increases in the concentrations of divalent cations Ca²⁺ contained in the pore fluid within the micro-pores were observed during both secondary and elevated temperature consolidation. These increases were considered to demonstrate the progressive deformation of micro-pores within the clay microstructures. The volume change of clay under constant rate of strain loading was presumably due to the deformation of the macro-pores. The main cause of "aging effects" from elevated temperature consolidation was shown to be the acceleration of secondary compression of the clay, which would have occurred during long term consolidation under normal temperature conditions.

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The shear strength of saturated sands under undrained cyclic loading is defined as transient shear strength in order to characterize its time dependency and to distinguish it from the undrained cyclic strength based on the equivalent cycle concept. It has been found from the undrained cyclic triaxial tests on two saturated Fujian sands that : (a) the transient shear strength of saturated sand is strain-rate dependent when the shear strain rate is more than 10% per second. In general, the transient shear strength of saturated sand consists of frictional resistance and viscous resistance, which can be described asτ_dt=τ_ft+τ_ηt=σ'_t tanφ'_d+ηγ_t; (b) the angle of dynamic internal frictionφ'_d is not affected by the number of cycles, consolidation stress ratio and frequency of cyclic stress (1-20 Hz) and the apparent viscosity coefficient η almost remains constant within the range of the tested shear strain rates (10-60% per sec) for a given density; and (c) the angle θ₀, formed by the phase transformation line in τ-σ plane, is nearly constant for a given sand. Furthermore, undrained cyclic torsional shear tests on hollow cylindrical specimens show that the frictional strength and the stress states at the phase transformation define two three-dimensional curved surfaces for the effective principal stress; and in addition, both of them can be described by the Matsuoka-Nakai criterion. Methods are proposed to determine the dynamic strength parameters and to correct the damping of the test apparatus system, the effect of inertia force of the sand specimen and the time lag of measured excess pore water pressure in cyclic triaxial tests with a higher frequency.

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In this paper, consideration is given as to how to characterize depth-variation for the small-strain shear modulus of natural clay sedimentation, in a state of normal consolidation. A case study was carried out for a relatively uniform clay layer deposited in the Holocene era. Initially, the effects of both strain and in-situ stress levels on secant shear modulus were carefully examined in cyclic torsion shear tests using undisturbed samples, which were recovered at different depths in a test borehole. The range of shear strain examined was between 0.001% and 1%. Similar examination was made for a silty clay using reconstituted samples that were isotropically consolidated at different stress levels. On the basis of the results of these laboratory tests, together with the shear modulus from an in-situ seismic survey, the small-strain shear modulus was formulated in terms of the stress and strain levels, and linked also to undrained shear strength. Interactions of the small strain stiffness between in-situ and laboratory are discussed in depth with an attention paid to the existing aging effect in the original subsurface condition.

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Contact friction coefficients for glass to glass surfaces were measured using glass beads with various diameters (ranging from 0.6 mm to 5 mm). The tests were conducted on two different friction testing apparatus (pulling and sliding devices). All particles were tested under equivalent normal stress ranging from 34.5 kPa to 207 kPa on clear or smoked glass plate with environmental conditions ranging from dry to flooded with tap water or flooded with motor oil. The test results indicated that the coefficients of static and dynamic friction increased when flooded with water. Meanwhile, the static and dynamic coefficients for a surface flooded by motor oil were slightly smaller than the ones under dry surface condition. The average coefficient of static friction was found to be O.162 (or 9.2°friction angle) for the dry clear glass surface environment and 0.277 (or 15.5°friction angle) for the water flooded clear glass surface environment.

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Standard deviations of stresses and displacements of differential settlements of a beam have generally been formulated by the author on the basis of wave number domain analyses, using a soil-structure system modelled as an infinite Timoshenko Beam on a Pasternak Model. The author has also proposed a probability-based prediction method for differential settlements of structures. The rotation which is the gradient of a line joining two reference points on the beam has not been formulated, although it is necessary for a probability-based prediction of the gradient of structures. In this paper the standard deviations of rotations of differential settlements of a beam, therefore, are formulated on the basis of wave number domain analyses and calculation diagrams are added to those previously published by the author for practical design.

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