A Study on Liquefaction Phenomena in Sand Layers Due to Surface Wave Propagation

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The purpose of this study is to determine the effects of surface waves on liquefaction behaviours of soft sand layers and sand mats on a soft clay layers. Brief outlines of the study are as follows:By. use of strong motion earthquake rescords observed at the Hachirogata Reclamation dike, where severe damage due to liquefaction was seen during the Nihonkaichubu Earthquake 1983, surface wave propagation characteristics were considered by means of equevalent linear analysis. Principal motion of the earthquake contains Love wave component and stress and strain in surface sand layers are found to be far greater than the ones by body waves. In case of array observation data in Shibata-cho, Miyagi Perfecture, Love waves were also found in the surface layer motion.In order to investigate stress-strain relationship of sand during surface wave propagation, torsional shear tests were executed on hollow cylinder sand samples. Influence of inherent anisotropy and induced anisotropy on shear behaviour of sand were investigated. The inherent anisotropy affects both stress strain relation and shear strength, while induced anisotropy affects only stress strain relation but shear strength.Response of pore pressure in sand layers were measured together with the velocity records at surface layers and base rock. There are some reports on field observation data of pore pressure, but none of reports was published so far on pore pressure together with base rock motions. In terms of observation results pore pressures were found to have strong relation to body waves, especially to S-waves.Considerations were also mentioned on the practical method of liquefaction prediction.