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

本研究的目的是确定表面波对软砂层和软粘土层上砂垫层液化特性的影响。这项研究的概要如下：利用日本中部地区1983年地震中液化破坏严重的八角围海堤的强震记录，用等值线性分析的方法讨论了面波的传播特征。地震的主运动含有Love波分量，表层砂层的应力应变远大于体波的应力应变。在宫城县柴田町的阵列观测数据中，表层运动中也发现了Love波，为了研究表面波传播过程中砂土的应力应变关系，对空心圆柱体砂样进行了扭转剪切试验。研究了固有各向异性和诱导各向异性对砂土剪切特性的影响。固有各向异性对应力应变关系和抗剪强度都有影响，而诱发各向异性只影响应力应变关系和抗剪强度。目前已有一些关于孔压现场观测资料的报道，但目前还没有关于孔压与基岩运动关系的报道。根据观测结果，发现孔压与体波特别是S波有很强的相关性，并对液化预测的实用方法提出了一些思考。

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.