Elastic wave propagation in saturated soil is investigated in order to grasp the frequency dependent wave propagation property of actual soil. First, a closed form solution of Biot's equation is derived under a one-directional wave propagation condition. Then, the frequency dependent properties of waves in various soils such as clay, silt, sand, gravel and soft rock are computed and discussed. The behavior is shown to be classified into three states : low frequency, high frequency and transient. Properties hardly change in the low and high frequency states. The degree of saturation is shown to hardly affect the shear wave property, but it greatly affects the dilatational wave property, especially in a highly saturated condition. Permeability hardly affects the properties at low and high frequency states, but it does change the frequency range of the transient state. Next, the applicability of Biot's formulation is examined and the high frequency state derived from Biot's equation is shown to be valid when permeability is larger than that of silt. Finally, it is shown that various mechanical properties can be evaluated using the frequency dependent characteristics of the wave, some of which are difficult to measure in situ with conventional tools.

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A triaxial testing system with local axial strain measurements was developed to accurately evaluate the time-dependent deformation properties of sedimentary soft rock. A series of consolidated triaxial creep tests were conducted on undisturbed samples of sedimentary silt-sandstone and mudstone. Drained creep tests, each lasting for three days, were performed at several deviator stresses in the course of drained triaxial compression. Creep axial strains measured locally at the lateral surface of the specimen were always noticeably smaller than externally measured ones, indicating significant time-dependent effects of bedding error occurring at the specimen ends. In these triaxial tests, the axial strain rate was stepwise changed during monotonic shearing to evaluate the effects of strain rate and its change on the stress-strain behaviour. It is shown that instantaneous irreversible strain and its rate uniquely control the current stress state whether the strain rate is constant or continuously changing. This isotach property is modeled in a simple model to be applied to the limited test condition examined. It is shown that this model can predict adequately the measured stress-strain-time behaviour for various time histories of strain (or stress).

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In order to compare one-dimensional compression behaviour with the crushing strength characteristics of single particles, one-dimensional compression and single particle crushing tests were carried out on various granular materials with uniform gradings. The average characteristic tensile stress acting on a particle in a sample was calculated using a simplified approach. The one-dimensional compression yield stress was related to the particle size and this was also related to the single particle crushing strength. The decrease of the vertical yield stress with increasing initial void ratio can be explained by the increase in the particle characteristic stress as the void ratio increased and a corresponding decrease in co-ordination number. The single particle strengths were compared with the characteristic tensile stress for a particle embedded in the soil matrix. The logarithm of the characteristic tensile stress at maximum compression index for a particle embedded in a granular matrix could be related to the logarithm of the single particle strength multiplied by a proportional factor. The introduction of a factor was necessary because the calculated average characteristic tensile stress did not take into account the non-uniform distribution of inter-particle stresses. The ratio of the single particle strengths to the average characteristic tensile stress for a particle embedded in the soil matrix was considered to be an indicator of the non-uniform distribution. This ratio decreased and hence uniformity of inter-particle stress distribution increased with angularity and surface roughness.

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A series of model tests was carried out on a particular type of sand (Toyoura sand) with a target void ratio of 0.66 to study into the effects of the shape and depth of a footing and the load inclination on the bearing capacity of a rough and rigid footing on sand. The test results were numerically simulated by two-and three-dimensional FEM analysis using a constitutive model that has been developed for Toyoura sand based on the results from an extensive series of laboratory stress-strain tests. The effects of the following factors, among others, on the strength and deformation characteristics of sand are taken into account ; a) pressure level ; b) the intermediate principal stress ; c) inherent anisotropy ; d) non-linear strain-hardening and softening ; e) non-associated dilatancy ; and f) strain localisation into a shear band (s). The material model is coupled with an isotropically hardening, non-associated, elasto-plastic material description. The FEM simulation is consistent with the physical model test results. In some important aspects, the results from both the physical model tests and FEM simulation are not consistent with some of the previous proposals that have been widely used in practice : i.e., in the results of the present study, the bearing capacity of a rectangular footing is noticeably larger than that under purely plane strain conditions, and negative effects of load inclination and positive effects of footing depth on the bearing capacity are generally larger than those predicted by some previous proposals.

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Research on the elastoplastic constitutive equations of soils has a long history. An elastic constitutive equation in a rate form is a key component of the full elastoplastic constitutive equation. However, a fully satisfactory elastic constitutive equation has yet to be found ; it remains an unsolved problem although it would seem to be quite simple. In this article a physically acceptable, yet simple elastic constitutive equation for soils in rate form is proposed and incorporated in the subloading surface model. The elastic bulk and the shear moduli are made to depend on the hardening function, defining the current yield surface, which plays the role of an internal plastic variable. The pertinence is verified by comparison with test data on sand.

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It has been reported by previous researchers that the preconsolidation pressure (P_c) of Kimhae (Yangsan) clay, which is thickly deposited along the Naktdong River, Pusan, Korea, is considerably less than its in-situ effective overburden pressure (p'_vo). The question has arisen whether such a low P_c value is due to underconsolidation or to the unreliability of laboratory tests, including the use of low quality sample. As a cooperative research program between PHRI (Port and Harbour Research Institute) and Pusan National University, extensive in-situ and laboratory investigations were carried out at Yangsan, using a Japanese sampler and Japanese sampling technique. It is found that the P_c values at the site are slightly greater than p'_vo, which is different from the test results from the previous researchers. However, the overconsolidation ratio (OCR) at this site is quite small compared to similar aged normally consolidated clays deposited in Japan.

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Sedimentary soils are formed due to the process of settling of soil particles in suspension. The settling process is physico-chemical in nature as the soil contains chemically active clay minerals. The extent to which the clay mineralogy affects the settling process depends upon the initial water content of the soil-water suspension. For montmorillonitic soils, the limiting water content at which the nature of settling changes from a discrete free type to a flocculated free type increases with an increase in the soil plasticity and decreases with an increase in the soil plasticity for kaolinitic soils. While the diffuse double layer repulsion controls this kind of behaviour of montmorillonitic soils, the behaviour of kaolinitic soils can be attributed to the fabric effect.

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Closed form solutions for vertically loaded piles in elastic-plastic, nonhomogeneous soil have been established recently using an ideal elastic-plastic load transfer model. However, in some cases, the load transfer from piles to the surrounding soil shows softening behaviour. In this paper, the established solutions are extended to account for this behaviour using a simplified strain softening soil model. The solutions are recast in non-dimensional forms, and expressed via modified Bessel functions. The effect of non-homogeneity and the degree of softening on pile capacity is explored.

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