In the seismic analysis of pile foundations the soil is often assumed to be an elastic material and the pressure at the soil pile interface is not limited during the analysis. This may result in a considerable error, as the computed pressure from an elastic analysis may go well beyond the ultimate lateral pressure of real soil. In fact, significant yielding at the soil-pile interface has been observed during real earthquakes, and also in laboratory tests. The yield zone is usually near the ground surface where the effect of inertial force due to the superstructure is higher. This yielding redefines the pile response, and in general cannot be ignored. In order to examine the effects of soil yielding on the internal pile response during earthquakes an approximate analysis is described in this paper which is an extension of a static method developed by the second author (1982) for the analysis of piles subjected to lateral soil movement. This method is then used to investigate the effects of soil yielding on the internal response of piles through a comparative study in which real earthquakes are used. It is shown that for strong earthquakes and heavily loaded piles the soil yielding may considerably increase the amount of maximum pile moment developed in the pile. A marked difference in the effects of yielding on the pile moment and shear is observed and discussed.

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The present paper aims at developing a simplified model for a stress-strain relationship at small strains up to an initial yielding of homogeneous saturated frozen sand. The modelling of elastic moduli for an ice-sand mixture as a composite geomaterial is first introduced based on previous studies, where a saturated frozen sand is treated as the icesand mixture. The applicability of modelling the elastic moduli under constant temperature is then discussed from the theoretical and experimental points of view. In addition, the hyperbolic stress-strain modelling of saturated frozen sand at small strain is presented. The effect of the volume fraction of sand, stiffness of sand inclusion and temperature changes on the elastic moduli and the stress-strain behaviour up to about 1-2% axial strain, which is defined as an upper yield stress, are investigated through the model, whose applicability is verified in comparison with the experimental data.

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The dynamic response of large-diameter end-bearing cylindrical shafts is studied. First, the popular plane-strain model of Novak is reviewed and its limitations are discussed. An improved model is then developed which, while retaining the simplicity of the original model, accounts for the third dimension by considering the normal and shear stresses acting on the upper and lower faces of a horizontal soil slice. These stresses are incorporated in the analysis by impleminting a dynamic Vlasov-Leontiev approximation based on integrating the governing equations over the thickness of the soil layer. It is shown that this operation leads to a set of elastodynamic equations which are similar to those in the plane-strain model, yet properly incorporate the salient 3-D effects. Explicit closed-form solutions are obtained for : (i) the dynamic soil reaction along the shaft ; (ii) the dynamic impedance of the shaft ; (iii) the displacement field in the soil ; and (iv) the dynamic interaction factors between neighboring shafts. Both vertical and lateral oscillations are analyzed for single and grouped shafts. Results are presented in terms of dimensionless graphs which highlight the importance of soil-foundation interaction on the response. It is shown that the proposed model avoids the limitations of the plane strain model.

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A series of permeability tests on both high-quality undisturbed samples and reconstituted samples was performed using a large-scale triaxial cell. Based on the test results and discussion, the following conclusions were noted. (1) The coefficient of permeability in the horizontal direction is larger than that in the vertical direction. However, its difference is between 10% and 70% and not so large. (2) The coefficient of permeability decreases with increasing confining stress. The effect of the confining stress can be understood as the effect of the void ratio. And the small change of the void ratio due to consolidation only leads to a small change of the coefficient of permeability. (3) There is no clear correlation between the physical properties and the coefficient of permeability. (4) The coefficient of permeability of gravelly soils is almost the same as that of sandy soils, even though the 50% diameter of gravelly soils is about ten to a hundred times that of sandy soils. This result implies that the large size particles of gravelly soils have no significant effect on permeability characteristics of gravelly soils. (5) A new definition for determination of D₁₀, D₂₀ and fines content only from those soil particles with a diameter smaller than 2mm was introduced. A correlation similar to sandy soils can be seen between the coefficient of permeability and D₁₀, D₂₀, and fines content based on the new definitions. (6) The effect of the small size particles of the gravelly soils on the coefficient of permeability was found significant based on the test results using samples with a special blend of particle size and density reconstituted from undisturbed samples. (7) The coefficient of permeability of multi-layer gravelly soils, in the direction perpendicular to the sedimentation, was significantly affected by the lowest permeability. And the coefficient of permeability of the multi-layer in total agrees well with the theoretical estimation. (8) Although the data is limited, there was no significant different of coefficient of permeability between undisturbed and reconstituted samples. This result accords with that reported for sandy soils by Hatanaka et al. (1997). This result also means that the coefficient of permeability of gravelly soil is not affected by the soil fabric. As a result, the in-situ coefficient of permeability of gravelly soils can be well estimated for practical purposes from the reconstituted samples with the same gradation properties.

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Non-linear stress-strain characteristics and stiffness-strain relationships of sedimentary soils and sands at small strains have been reported by many researchers. Research work on the behaviour of weathered or decomposed granites at small strains, however, has rarely been reported. This paper compares some stiffness measurements of decomposed granites from field investigations involving crosshole seismic, self-boring pressuremeter (SBPM), and high pressure dilatometer as well as results from laboratory tests using bender element and internal transducers. The in-situ crosshole measurements show that the elastic stiffness of Moderately Decomposed Granite (MDG, approximately 7000 MPa) is about 25% greater than that (about 5500 MPa) of Highly Decomposed Granite (HDG), which is in turn approximately 18 times higher than that (about 300 MPa) of Completely Decomposed Granite (CDG). This is likely attributable to the materials'different bond strengths and structures. A new method has been adopted to interpret the SBPM data. Measured data from crosshole seismic and self-boring pressure meter tests for CDG are found to be consistent. Bender element laboratory tests on CDG indicate that the measured A-coefficient in the expression of G_o/p_r=A (p/p_r)ⁿ lies between the results from clay and sand as reported in the literature. However, the measured nvalue for CDG is generally larger for clays and sands. The measured bender element results are consistent with data from internal transducers. Highly non-linear characteristics of CDG were observed in both the laboratory and field tests. Generally the elastic stiffness of CDG as determined by laboratory tests is about 50-80% of that from field tests. Some possible reasons are discussed.

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The Hualien Large-Scale Seismic Test (HLSST) program is under way to investigate soil-structure interaction during earthquakes in Hualien, a high-seismicity region in Taiwan. Since anisotropic characteristics of the gravelly layer affect the results of earthquake observation and forced vibration tests, the gravelly layer was modeled by an orthotropic elastic body in this paper to enhance the accuracy of the dynamic simulation analysis. The following conclusions are drawn. (1) The gravelly layer was modeled by an orthotropic elastic body whose model parameters were partly determined using results of earthquake observation. (2) The azimuth dependency of the shear wave velocity measured by the cross hole velocity logging can be expressed by the orthotropic elastic body model. (3) It can be explained by the orthotropic elastic body model that values of shear wave velocity measured by down-hole velocity logging were divided into two groups. (4) The initial shear moduli of undisturbed samples from the gravelly layer evaluated by cyclic triaxial tests agree with the calculated results by the orthotropic elastic body. (5) The anisotropic behavior of the model building during forced vibration tests can be expressed successfully by the orthotropic elastic body.

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This technical note extends the application field of the method proposed by the author (Greco, 1999) to walls subject to seismic conditions analyzed by the pseudo-static method of Mononobe and Okabe. The active thrust is calculated maximizing its horizontal component (or minimizing its vertical one) with respect to the inclination angles of the planes bounding the thrust wedge. This also corresponds to minimizing the safety factor against sliding along the base. Cantilever walls with both elongated and short heels are studied in this note.

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