Applicability of chemical grouting for the improvement of liquefaction susceptibility of saturated sandy deposits

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The fact that sandy deposits treated by chemical grouting show good resistance to liquefaction during strong earthquakes is well known. The fundamental mechanisms leading to resistant behavior remain unknown up to the present time. In order to get insight into the mechanisms, several experimental works have been performed in this research project. In particular, the increase of resistance to liquefaction treated by a low-content silica was investigated in detail, which leads to the improvement of sandy deposits with reasonable costs. The application of chemical grouting for the purpose of the improvement of sandy deposits to practice requires the numerical analyses on the distribution of grouting and strength. For the proper analysis of the problem requires the well behaved constitutive model with account for the effect of dilatancy and increase of strength. In addition to chemical grouting, cement paste was used as an alternative material leading to the increase of the resistance to l … More iquefaction. The main results obtained through this study can be summarized as follows :1.Cyclic triaxial tests were performed on the specimen with varying the contents of silica. The specimens with the contents more than 3% show the change in dilatancy with the tendency of expansion, which is believed to result in the resistant behavior to liquefaction;2.The specimens with the content less than 3% show little difference in strength and dilatancy behavior, although shear deformation shows a little increase after initial liquefaction (pore water pressure reaches to the initial effective confining pressure), which reduces the possibility of complete (catastrophic) liquefaction. This fact may indicate the fact that low hydraulic conductivity of treated specimen with low content of silica prevents the specimen from showing catastrophic liquefaction failure, which is partly supported by the quick sand test with the result that the treated sand shows high resistance to quick sand and needs a long duration until final failure occurs.3.In addition to chemical grouting, the cement paste which leads to the higher strength were used as a material for improving sand deposits. For the purpose of injecting the liquid with high viscosity, the method with varying the injection speed was found effective.4.To understand the overall mechanical behavior of treated sand with silica and cement, the homogenization technique was applied to bridge the micromechanical behavior and macroscopic behavior. More study is required to apply the method to the complex material.5.The severe damages due to liquefaction are believed to occur with the flow of sandy deposits during and after strong earthquake excitation. The constitutive model was developed in order to account for the effects of change in density of sand and was applied to the problem of flow due to the movement of pore water.These results were fully discussed in the research report (in Japanese). Less