水深对水下地基场地地震动影响的时域分析

利用地震波斜入射下水下地基场地地震动分析的一维化时域算法,推导了平面P波入射下,水下地基场地的位移、加速度和应力表达式,重点分析了水深变化对位移峰值、加速度峰值、剪应力峰值和孔隙水压力峰值沿土层深度的分布规律。数值结果表明:同一土层深度处,当水深不超过1倍的土厚时,竖向位移峰值随水深的增大而增大;当水深超过1倍的土厚时,竖向位移峰值随水深的增大而减小。水平位移峰值与水深的关系基本上与竖向位移峰值相反。同一水深下,竖向位移峰值沿土深不断减小,水平位移峰值呈先减小后增加的趋势。同一水深下,竖向加速度峰值沿土深是一个不断减小的过程,水平位移峰值是一个反复增大和减小的过程。在0.75倍的土厚到基岩的范围外,水深对剪应力峰值的影响均较小。孔隙水压力峰值沿土深的分布大致是先减小再增加最后减小。

Time Domain Analysis of Effects of Water Depth on theDynamic Responses of Underwater Site

Based on the 1D time domain method for dynamic response analysis of underwater site subjected to obliquely incident seismic waves, the expressions of displacement, acceleration, and stress of underwater site under the incidence of plane P-waves were derived. The effects of water depth on the peak displacement, peak acceleration, peak shear stress, and peak pore water pressure along the vertical depth of soil layer were explored. The numerical results showed that at the same depth of soil layer, when the water depth is less than 1 time the soil thickness, the peak vertical displacement increases with the increase in water depth; when the water depth is greater than 1 time the soil thickness, the peak vertical displacement decreases with the increase in water depth. The relation between peak horizontal displacement and water depth is basically the opposite of the peak vertical displacement. Under the same water depth, the peak vertical displacement and peak vertical acceleration continuously decrease with the increase in soil depth, and the peak horizontal displacement decreases first and then increases. Beyond the range from 0.75 times the soil thickness to the bedrock, the water depth has little effect on the peak shear stress. First, the peak pore water pressure generally decreases and then it increases and decreases gradually.