When a saturated sand is subjected to earthquake excitation under undrained conditions, excess pore water pressure is generated, and the effective stress decreases. This eventually leads to sand liquefaction. It is important to analyze the liquefaction phenomena, particularly for the earthquake-resistant design of structural foundations. Although many experimental studies on liquefaction have been performed, their results have not well implemented in developing analytical models. In this study, the dynamic response of horizontally layered soil is numerically analyzed, using the stress-strain relation of sand and the equation of motion for two-phase mixtures consisting of an incompressible fluid and an elastic-plastic solid. As the mixture of pore water and soil particles is assumed to be incompressible, effective stress analysis is appropriately applied. In the case of a horizontally layered soil deposit, deformation should be horizontally confined during earthquakes. In this study, therefore, the horizontally confined condition is considered. By using this condition, stress path particular to the liquefaction process can be obtained analytically. The effect of the dissipation of pore water pressure due to seepage on the response of the ground is also examined. It is concluded that liquefaction greatly influences the dynamic response of ground.

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Immediately after the Miyagiken-Oki earthquake of June 12, 1978, the authors found 38 liquefaction sites. At most of these sites, settlement of river dikes, uplift of sewage tanks, tilting of quay walls and other damage were caused by liquefaction. At some liquefaction sites, no structural damages were observed. The degree of liquefaction at each liquefaction site, the ground conditions, the relation between liquefaction and resultant damage, and the characteristics of liquefied sand are discussed in this paper. Sedimentary environments of boiled sands are inferred by grain size distributions at nine liquefaction sites. Moreover depths of liquefied layers at two sites are estimated based on the correlation between the grain size distribution of boiled sand and that of soil samples.

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Detailed soil investigations were conducted by means of the standard penetration test and Dutch cone penetration test, together with sampling by means of the large diameter sampler and Osterberg type piston sampler at two sites in the city of Niigata, Japan ; one where liquefaction type failure had occurred, and the other where liquefaction type failure had not occurred during the 1964 earthquake. Undisturbed loose samples of sand were tested in the laboratory using the cyclic triaxial test apparatus. The cyclic strength thus determined at each depth of the deposits at the two sites was incorporated into the simple liquefaction analysis which was carried out on the basis of the ground surface acceleration records obtained at the basement of a nearby apartment building during the 1964 earthquake. The results of the analysis indicated the behaviors of two sites that were in accord with the actual performances observed at the time of the earthquake.

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A computer program using finite element techniques is developed in this work to analyze the partially-drained behavior of an elasto-viscoplastic material under three-dimensional axi-symmetric loading conditions. Tests of the program show that the results are comparable to published solutions for two typical consolidation problems. It is then shown that the results from the analyses of partially-drained, conventional triaxial testing of a normally consolidated clay compare favorably with the measured results over a wide range of partially-drained states. It is proposed that the partially-drained triaxial testing can be classified into three categories : fully-drained ; intermediate ; and fully-undrained, in terms of a dimensionless rate parameter dE_Z/dT. Furthermore, a method of accounting for the efficiency of filter paper drains in the triaxial testing is presented.

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The explanation is performed about the modified triaxial apparatus which can independently control three principal stresses. This apparatus can generate different principal stresses in the cubic specimen by means of the loading system placed in the conventional triaxial chamber. By using this apparatus, the drained shearing tests are carried out under general stress conditions including the repeated loading and the test results are shown. The used material is sandy soil called Toyoura sand. The numerical experiments are also carried out by applying the mechanical model which has been proposed by the author (Kitamura, 1981 a, b) to the mechanical behaviours of particulate material. The results of numerical experiments are compared with the stress-strain relations of Toyoura sand under general stress conditions. From the comparison of these results, it clear that the proposed model can follow the mechanical behaviours of particulate material by using several model parameters, which reflect the mechanical properties at the particle scale, when the energy transferred into or out the specimen, the initial void ratio and the distribution of contact angles are known. Thus, it may be concluded the proposed model is a unified, simple and comprehensive one that can express the various mechanical behaviours of particulate material.

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Soil disturbance caused by boring and the stress relief of soil around a borehole left unsupported may influence the parameters obtained from the Menard pressuremeter (abbreviated as MP). The paper presents the results of tests obtained from a self-boring pressuremeter (abbreviated as SBP) devised by the author for a variety of soils such as soft clay, loose sand dense sand distributed in the northern coast of Tokyo Bay. The instrument containing self-boring mechanism is statically penetrated into ground, digging a hole simultaneously. The undrained shear strength of soft clay obtained from the SBP test was well correlated with that obtained from undrained triaxial tests for undisturbed samples reconsolidated under the pressure equivalent to the effective mean stress in situ. The shear modulus during undrained deformation of soft clay obtained from the SBP test was, in general, well correlated to that obtained from triaxial tests. The strength and modulus of cohesive soils were considerably under-estimated by unconfined compression tests.The shear modulus obtained from the SBP was approximately 2 to 7 times greater than that obtained from the MP test. For the soils investigated, aside from loose sand, no significant difference in the limit pressure was conceived between the SBP test and the MP test.

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Both original and shear-induced fabrics have a significant influence on the deformation and strength properties of clays. The shear-induced structure appears to be the prime cause for the formation of constant residual angle irrespective of the stress history or the initial structure. Initiation of shear-induced fabric is controlled by the mobilization of true angle of friction. A comparison of true and residual friction angles from field data is made. The correlations of Bjerrum for residual friction angle and Skempton-Gibson-Bjerrum for true friction angle with plasticity index have been used to get additional data for the comparison. It is found that the residual friction angle is nearly equal to true friction angle for soils with clay content greater than about 40%. Residual friction angle approaches true friction angle at low normal pressure in soils with high percent of montmonillonite.

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A simple and accurate method for automatic measurement of volume changes of saturated test specimens in laboratory tests is described. In this method, the volume change of water in a burette is measured with use of an extremely sensitive differential pressure transducer. Any value of back pressure less than 3000 kN/m² can be used in this method. The volume change is monitored with a digital voltage meter. The sensitivity of the method is 0.006 ml/mV over a range of 25 ml or 0.0013 ml/mV over a range of 5ml.

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