地下水位上升对上海软土场地地震反应的影响

Effect of rise of groundwater table on seismic ground response of soft soil in Shanghai

根据工程地质勘探和室内外试验建立上海软土场地计算模型,采用Biot动力固结理论,结合弹塑性边界面模型,研究三向地震作用下地下水位上升对场地土层地震反应的影响。利用具有水平和垂直三向完整加速度记录的Taft波构造基岩输入地震动时程曲线,分析三向地震作用下地下水位上升对土层竖向和水平加速度放大效应、竖向与水平加速度峰值比、地表加速度和反应谱特征以及沿土层深度最大孔隙水压力和孔压比的影响。计算分析表明:地下水位上升对水平向和竖向峰值加速度的放大效应影响差异显著,同时对地表加速度及其反应谱特征具有重要影响。地下水位的上升,地表水平峰值加速度放大效应增大,竖向峰值加速度放大效应减小;竖向与水平向加速度峰值比减小;土层高频滤波作用增强,长周期成分放大效应增大;近地表液化土层范围增大,加剧砂土液化危害性。

A dynamic model is developed based on the results of geological investigations as well as laboratory and field tests in Shanghai.The Biot＇s dynamic consolidation theory and reduced order bounding surface model are coupled to study the effect of the rise of groundwater table on the seismic ground response of soft soil undergoing 3-D seismic base excitations（which are obtained from Taft）.The effect of the rise of groundwater table on the horizontal and vertical amplification factors,the ratio of vertical to horizontal peak acceleration,the characteristics of acceleration and response spectrum at ground surface as well as the maximum pore water pressure and pore water pressure ratio along the depth of soil layer are studied.The results show that the rise of groundwater table has dramatically different influences on the horizontal and vertical amplification effect as well as the characteristics of acceleration and response spectrum at ground surface.As the result of the rise of groundwater table,the amplification effect increases in horizontal direction but decreases in vertical direction.The ratio of vertical to horizontal acceleration decreases.The filtering effect on the acceleration with high frequency and the amplification effect on the acceleration with long period increase.The range of liquefiable soil near ground surface extends and hazard risk increases.