The effect of density on the drained deformation properties of pyroclastic flow deposits, so called Shirasu, distributed in the Southern Kyushu, Japan, was investigated by using a triaxial testing apparatus with independent stress-control systems. Hydrostatic compression tests and radial shear tests maintaining a constant mean principal stress were performed on Shirasu specimens prepared by pluviation through water. The test results indicate that the reconstituted specimens of Shirasu were characterized by an inherent cross-anisotropy and a density-dependence of their deformation properties. In general, the specimens had a low compressibility and a high expansibility in the direction of specimen-deposition compared with the direction along the bedding plane. The maximum shear strength in the identical stress state having different stress-path occurred when the major principal stress was applied to the direction of the specimen-deposition. The change of the deformation-strength properties was caused by the change of strain increment ratio which depends on the dilatancy occurring under the different stress path.

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Investigated is the relation between the hydrofracturing pressure P_f and the strength of cohesive soils. Fracture tests on six kinds of cohesive soils (i.e. φ=0 materials), including artificial soils, were performed. The direction of fracture surface was chosen not only vertical (i.e. parallel to the borehole) but also horizontal and inclined. The result is the following equation in terms of total stress.P_f=σ_min+q_u σ_min : the minimum principal stress, q_u : the unconfined compression strength The shear failure-rather than the tensile failure-near the borehole initiates the hydrofracture of cohesive soils. This fracture mechanism seems to be reasonable, especially in case of the horizontal or inclined fracture. The viscosity of liquid in the borehole, the sample size and the pre-existent crack around the borehole have little influence on the fracturing pressure as far as the pressurizing rate is high enough to prevent the liquid to penetrate into the wedge.

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A formulation for the compression of sedimentary soils was attempted by separating the compression type into the rapid process of upper sediments and slow process of subsoils, based on both the experimental results and theoretical consideration.It is shown that the fundamental equations proposed can well explain the characteristics and behaviour of the compression of soils. The theoretical relationship between compression index and void ratio ensured the empirical relationships.Further, the results obtained indicates that the virgin compression curve to be predicted from the results of consolidation test may not accord with that of the true virgin compression. Therefore, it is likely that the conventional prediction method for settlement will underestimate or overestimate settlements.

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Described is a numerical procedure to back-analyze the nonlinear constitutive parameters and permeability from the monitored movements of subsoil under two-dimensional consolidation. The difficulty in the back-analysis of nonlinear constitutive parameters lies on the fact that most of the nonlinear constitutive models employ the stress as the fundamental variable to govern the change in the deformation moduli and to specify the yield criterion, and that the stress is little sensitive to the change in deformation moduli. At first, the authors devise a simplified hyperbolic stress-strain model in which the shear strain is the variable controlling the decrease in deformation modulus and in which the shear strength is not related to the confining pressure. The unknown soil parameters to be back-analyzed are the initial tangent moduli of rigidity, the shear strengths and the permeabilities in multiple soil layers. By combining FEM and mathematical programming technique, the procedure allows to correct the unknown soil parameters until the differences between calculated and measured quantities decrease sufficiently. The proposed procedure is verified by calibrating the performance of the procedure being applied to hypothetical case studies. Subsequently the procedure is applied to actual case studies and comparisons are made with the results obtained by assuming the linear elastic behaviour of soil deposit. By applying the proposed procedure of back-analysis to the observational procedure in construction phase, one can get the rough estimate of shear strength at each time stage of construction.

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In order to take a knowledge on the seasonal variations of groundwater level and pore water pressure in landslide areas, the field investigations were carried out during five years. Based on the field investigation, the following conclusions can be drawn : 1) Groundwater level and pore water pressures at the slip surface in landslide areas have changed seasonally, with marked increases after the snow-melting and heavy rainfall seasons.2) Pore water pressures at the slip surfaces do not always coincide with hydraulic pressure values calculated from the groundwater level. Therefore, when making slope stability analyses and taking preventive measures against reactivatings, pore water pressures should be measured directly all along the slip surface with electric piezometers.3) Landslide is liable to occur during two weeks after heavy rainfall because of time lag between groundwater level and rainfall, therefore, the careful attention should be necessary for these period.4) The slope stability analysis should be conducted on the shearing strength considered the overconsolidated states of soils due to the increasing of pore water pressures.

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In this study we examine a method based on Mindlin's solution in order to estimate the load-settlement behavior of piles and pile groups for rational design of pile foundations. First, the theoretical aspects of the previous method proposed by Poulos and other investigators are briefly presented. Some modifications are made to the method so as to consider additional factors such as soil non-linearity and multi-layering. Next, in order to evaluate the numerical accuracy, vertical displacements and axial forces of pile groups or single piles embedded in non-homogeneous soil calculated by the previous method and by the modified method are compared with values calculated by more sophisticated methods such as the boundary element method and the finite element method. As a result, we conclude that, from a practical point of view, the modified method based on elasticity is sufficiently accurate in regard to axial force distribution as well as settlement. We also propose tentative input soil constants for immediate settlement using solely the results of SPT. Finally, the values of pile top settlement calculated by the modified method are compared with the results of 26 field vertical load tests on cast-in-place concrete piles. The results show that the calculated values coincide approximately with the measured values, meaning that the proposed modified method of calculation and the proposed input soil constants seem to be adequate for the preliminary estimation of immediate settlement of cast-in-place concrete piles.

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Paying attention to the important mechanical features peculiar to granular materials : friction and dilatancy, fundamental considerations on the deformation of sand under simple shear condition are made. First, adopting the simple sliding block theory, the two state functions of ψ and S are analitically derived and a basic deformation model is formulated. This simple model is found to be a good approximation in the intermediate range of stress ratio. Next, using the experimental data, the entropy of granular materials S is examined. Another deformation model based on the characteristics of the state parameter S can be extended to wider range of stress ratios.

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The behavior of granular piles with different densities and different proportions of gravel and sand on soft Bangkok clay was investigated. A total of 13 piles were installed with 0.30 m diameter and 8.0 m long using a non-displacement cased borehole method with 1.20 m spacing in a triangular pattern. The piles were grouped into 5 categories. Groups 1, 2, and 3 with 3 piles each, were constructed using sand compacted at 20, 15, and 10 hammer blows per layer, respectively. Group 4 was made of gravel mixed with sand in the proportion on 1 : 0.30 by volume and group 5 was constructed with gravel ; both groups consisted of two piles each were compacted at 15 blows per layer. Four active and 2 dummy piezometers were installed for monitoring pore pressures. The soil properties were investigated by the field vane and pressuremeter tests. The ultimate capacity of each granular pile was determined by using full scale plate load tests. Using the pressuremeter results and the method by Hughes et al (1975), the predicted ultimate pile capacity and load-settlement curve agreed well with the experimental data. The maximum bulge in the pile was observed to be about one pile diameter from the ground surface. It was found that the pile made of gravel with 15 blows per layer (Group 5) yielded the maximum ultimate pile capacity closely followed by the piles constructed out of sand with 20 blows per layer (Group 1). In an earlier investigation (Bergado et al, 1984), it was found that the ultimate pile bearing capacity was 3 to 4 times greater than that of the untreated ground and that the piles acted independently when the spacing was 3 pile diameters or greater.

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Sand compaction is a useful method to mitigate liquefaction. In actual design procedure, there is a need to determine an adequate compaction depth and width. Unlike the compaction depth, it is relatively difficult, however, to determine the suitable width of compaction area.This paper investigates the effects of the width of the compaction area, the width of the structure, and the height-to-width ratio of the structure on the settlement of the structure due to sand liquefaction.A series of shaking table tests on saturated sand bed-model structure system was conducted to take into account the above three variables. A special method was developed for preparing model ground with densified area. It can be concluded from the shaking table test results that the settlement of the structure decreases with increasing width either of the densified area or of the structure, and with decreasing height-to-width ratio of the structure.

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