This paper is concerned with the formation of the shear bands by employing the finite element method with a non-coaxial Cam-clay model developed in our last paper (Yatomi et al., 1989). This finite element method for finite strains is formulated as a soil/water coupling form based on the updated Lagrangean scheme. A demonstration of shear bands formation is given in a classical rigid punch problem without introducing any initial imperfections into the material elements.

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In order to investigate the mechanism of hydraulic fracturing in soils, several laboratory tests are performed on compacted hollow cylindrical specimens of a cohesive soil under different confining pressures. The results indicate that hydraulic fracturing in soil initiates when total stress near the borehole reaches to the failure condition of the soil in unconsolidated undrained state. Based on Mohr-Coulomb failure criteria, theoretical solution of hydraulic fracturing pressure is derived and physical meanings of empirical equations appeared in previous papers are discussed. Then the general expression of hydraulic fracturing in pore pressure existance is obtained.

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The importance of seismic observation for evaluation of soil-structure interaction has been emphasized. To fully understand the meaning of recordings on and around the building foundation, however, we must first explore the nature of the ground surface motion near the foundation. In this paper the boundary element method is used to analyse the ground surface motion around a cylindrical foundation subjected to incident body and Rayleigh waves. The study shows that, a shadow zone is formed behind the foundation on the opposite side of the incident waves, in which the ground surface motion is smaller than that of the free field motion in high frequency range. When the non-dimensional frequency a₀≥2 (or the ratio of the foundation's radius to the wavelength of incident waves a/λ≥0.3), there will be a remarkable reduction of amplitudes. For incident body waves, when incident angle and the embedment ratio of the foundation become larger, the corresponding reduction effect becomes greater. For incident Rayleigh waves, the reduction of amplitudes is very pronounced and the bound of the reduction extends widely, regardless of the embedment ratio. The plane distribution of the reduction range and the effect of the flexibility of the foundation on the reduction have also been analysed. Afore-mentioned phenomenon can be interpreted in terms of screening of incident waves by the foundation. The experimental studies on the isolation effect of a screen aiming to decrease vibration of structure backed up these analytical conclusions.

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The current design procedure for an embankment constructed in a mountainous region does not take into account the influence rainfall run-off from the surrounding valleys in the quantitative determination of a safety factor. A number of road embankments in the mountainous areas of the Noto Peninsula failed due to the heavy rainfall in July, 1985. After site investigations were completed, it was found that those failures may have been triggered mainly by the rainfall run-off from the surrounding valleys. It is therefore considered unneglectable in a geotechnical engineering practice to introduce the degree of influence of rainfall run-off on the stability of embankments in mountainous regions. This paper describes a proposed design procedure for embankment in mountainous area making it possible to evaluate the safety factor considering the influence of rainfall run-off. In this proposed design method new indices are defined in order to quantitatively determine both the rate and amount of rainfall run-off. Thus proposed design procedure is effective to determine both the optimum safety factor against heavy rainfall for the embankments and the most appropriate countermeasures to be taken immediately, if necessary, for embankments already constructed. It is shown that this methodology is quite suitable and easy to apply from a practical engineering point of view.

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A study of the effects of prestrain history on the subsequent monotonic and cyclic undrained reloading behaviour of a saturated sand that is contractive in the virgin state is presented. An effective stress boundary is proposed that distinguishes between small and large prestrain. Effects of the level and the sense of preshearing together with the manner of inducing prestrain are investigated for sand with both isotropic and anisotropic consolidation histories. Rational explanation is provided for the observed effects of preshearing by a detailed look at the effective stress conditions during preshearing and subsequent reloading.

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An analysis of a saturated sandy subsoil behaviour due to cyclic loading is presented. Cyclic loads create cyclic shear strains in a subsoil, and subsequently cause pore pressure generation that leads to the reduction of the shear strength of a subsoil and, in an extreme case, to the failure of structures founded on such soils. A pore pressure generation is accompanied by a process of pore pressure dissipation which reduces a rate of pore pressure generation. The assumption of undrained behaviour (no dissipation effects) allows for obtaining the "lower bound estimate" of subsoil behaviour, since the pore pressure dissipation effects make the rate of pore pressure generation smaller, and then we need more loading cycles to get the onset of liquefaction. An analysis of the problem of simultaneous pore pressures generation and dissipation is very much complicated because the differential equations describing these phenomena are coupled. We have proposed a numerical procedure which allows for studying this problem in a relatively simple manner. The pore pressure generation in a subsoil is computed with the help of the compaction theory which is formulated in terms of the cyclic stress and strain amplitudes. The pore pressure dissipation is computed with the help of a simplified version of the Biot theory. The process of resolidification starts when the action of cyclic loadings is over. The excess pore pressures now freely dissipate down to the equilibrium. We can also study this behaviour. In our contribution we present the fundamentals of the compaction theory, numerical algorithm of dealing with boundary value problems, as well as some numerical examples regarding the behaviour of a subsoil beneath a breakwater.

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After the Owi Island observation program was terminated, a new recording station was established at Sunamachi, Tokyo Bay, in 1986 to monitor pore water pressures and accelerations during earthquakes. On December 17, 1987, an earthquake of magnitude 6.7 shook the area of Tokyo Bay and a set of instruments picked up the motions and pore water pressures. The maximum ground surface acceleration recorded was 122 gal and the pore water pressure rise in the sandy deposits at depths 7 to 13 m was 6% to 14% of the mean effective confining pressure. On the basis of the laboratory test results performed previously on undisturbed samples, an estimate was made of the pore pressures that might have been produced in the deposit by the seismic shaking with a peak acceleration of 122 gal. The estimated values of pore pressure were shown to be in satisfactory agreement with those monitored during the earthquake.

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In an effort to develop a constitutive equation associated with more deformation and failure features of granular materials, the constitutive formulation is studied taking into account the fabric tensors as internal variables and their evolution modes. In order to render the constitutive equation satisfy the principle of material objectivity, the representation theorem of isotropic functions is effectively used. The theorem is reviewed with a particular reference to the rate type constitutive equation which gives rise to the rate of deformation tensor as a function of the stress, stress rate and fabric tensors. After discussing the relationship between essential independent variables in constitutive equations and the state of granular materials from a viewpoint of the evolution mode of the fabric tensors, particular problems are studied with the result that : (1) Granular materials can show less summetry (more anisotropic) than orthotropic when the general stress states and paths are concerned ; (2) In two dimensions, the introduction of the (anisotropic) fabric tensor is essential in order to describe the non-coaxial and dilatant behavior under the rotation of principal stress axes.

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The results of laboratory experiments performed to investigate the effects that factors such as fabric, anisotropic consolidation and stress-strain history have on the shear modulus at very small strains (G₀), on the drained modulus degradation curve, and on the cyclic undrained shear strength of sands are summarized. The results presented show that G₀ is relatively insensitive to sand fabric, initial stress ratio, monotonic prestressing, and cyclic strain history. Thus, specimens with the same G₀ can exhibit very different behaviors in cyclic undrained shear, depending upon their initial fabric, initial stress ratio, or stress-strain history. To a lesser degree, this is also true for the shear modulus (G) at larger strains, as interpreted in the conventional manner from drained cyclic shear tests (unload/reload modulus). Based on these findings, the limitations involved in the use of G₀ and G to interpret behavior in cyclic undrained shear are discussed.

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Prediction of bending moments of a batter pile installed in subsiding clay ground is presented. The analysis is based on the assumption that loads acting on the upper part of a pile are similar to the case of a positive project conduit and the lower part of the pile behaves as an elastic beam on Winkler's model. The computed values are compared with the measured values on the prototype of piles tested in a clay ground. From the result obtained, it is concluded that the theoretical values are somewhat larger than the measured values. Diagrams with nondimensional parameters are prepared for designing of pile foundations.

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This paper investigates the volume ratio α of grout entered into void space in each part of solidified region by chemical grouting for the sandy ground. In long gel time grouts, the value of α is in 80∼lOO% unless the hydrofracturing occurs and α does not practically depend on the distance from the injection borehole. On the other hand, in short gel time grouts, α of the region near to injection hole is more than 100%, because the pore gel in the solidified body is concentrated when the succeeding grouts penetrate the solidified body. As a whole, the solidified volume is almost equal to the solidified volume when α is supposed to be 100%, irrespective of the gel time of grouts, as long as the injection rate q is smaller than the critical injection rate qCR. qCR is the maximum value of injection rate which does not initiate the hydrofracturing of ground.

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