A newly designed direct shear apparatus was developed to prevent obstacle friction which occurs between the side wall of shear box and a sand sample during a shear test under a CD-test due to dilatancy behavior of a sample. A couple of independent air jacks with load cells were mounted on the upper counter plate. This system allows the upper shear box to move up and down without tilting during shearing, and, as a result, vertical stress, σ N , can be measured correctly using the upper mounted load cells without influence of friction. A series of CD-tests using the apparatus on Toyoura sand were conducted in order to compare shear properties including shear strength obtained using an ordinary type of direct shear apparatus (Mikasa's direct shear apparatus) and an ordinary triaxial compression apparatus. It was found that strength obtained using the new apparatus gives the same strength as that obtained by CD-tests using a triaxial apparatus and that obtained by CU-tests (φ') using Mikasa's direct shear apparatus. However, CD-tests using Mikasa's direct shear apparatus give 2 to 3 degrees of excessively higher strength. This shows that the developed new system for direct shear apparatus works effectively to prevent the influence of friction problem of CD-tests on sand samples.

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Recently, regional ground upheaval phenomenon caused by the rise in groundwater level has been observed in an urban area, and its effect on underground structures is concerned. In this study, at first the observed ground upheaval distribution in Tokyo city was reported. Secondly, in order to clarify the mechanism of ground upheaval with the rise in groundwater level and to establish the prediction method, the centrifuge model tests and numerical simulations using the one dimensional consolidation theory proposed by Mikasa were conducted. The centrifuge model test showed that the isochrone of pore water pressure become the non-linear distribution at the steady state after dewatering process, and the ground upheaval phenomenon with the rise in groundwater level was clearly observed. In numerical simulations, the effect of permeability coefficient of non-linear isochrone of pore water pressure was discussed. Analytical results showed the same tendency as the test results in the analytical case with porosity-dependent permeabilities. The results showed that the validity of the prediction method and the importance of determinating the permeability coefficient of clay in the ground upheaval analysis.

A newly developed direct shear apparatus for cyclic tests is, first, introduced. It is shown that liquefaction strength on Toyoura sand obtained using a newly developed direct shear apparatus and test procedure coincides well with that obtained from cyclic triaxial tests. Then, two series of cyclic direct shear tests were carried out on samples of sandy silt, which was excavated by a grab bucket at a construction site in Naruto City, Tokushima Prefecture. Therefore, considerable disturbance was expected. Results were compared with those from a series of cyclic triaxial tests on undisturbed samples by a triple-tube technique at the site. It was found that liquefaction strength from the direct shear tests coincided well with that obtained from cyclic triaxial tests. It is deduced that disturbance of a sample was well cured in the consolidation process, which is one of the advantages of the newly developed apparatus.

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