基于动土压力影响的坝基动剪切模量反演研究

Inverse analysis on dynamic shear modulus of earth-rockfill dam foundation based on the influence of dynamic earth pressure

对于土石坝的坝基中土体应力-应变关系的求解,由于非自由地表以及土体所受水平正应力变化的影响,理想一维剪切梁模型方法并不适用。利用下覆饱和砂土地基的土石坝离心振动台试验,分析了不同输入地震峰值下非坝体覆盖区地基、坝中、坝趾处土体加速度的响应规律,得到了坝基中上部土层动土压力在水平向的变化特征,提出了考虑水平向动土压力影响的坝基土体剪应力-剪应变反演计算方法,并与利用理想一维剪切梁模型所绘制的应力-应变滞回圈对比,分析了动土压力对坝基土动剪切模量的影响。结果表明:由坝基底部至坝顶,加速度的放大效应基本呈线性增大;土压力在水平向的变化情况在剪应力-剪应变反演计算中不能忽略;考虑水平向动土压力的影响后,土体剪切模量的计算值减小。随着深度增加,动土压力对坝基中部土体剪切模量的影响比上部土体更大,且计算相对误差随着深度和输入地震波峰值加速度的增加而变大。

The one-dimensional shear beam model method is unsuitable for determining the stress-strain relationship in the earth-rockfill dam foundation because of the constrained ground surface and the effects of the lateral normal stress.A centrifugal shaking table test was conducted on an earth-rockfill dam with overburden saturated sand foundation to analyze the soil acceleration response in the non-dam-covered area of the foundation,middle and toe of the dam under different input seismic loads.This test also obtained the variation characteristics of the horizontal dynamic earth pressure in the upper and middle layers of the dam foundation.An inverse calculation method was proposed to obtain shear stress-strain in the dam foundation soil,considering the influence of horizontal dynamic earth pressure.Comparing it with the stress-strain hysteretic loop inversed through the ideal one-dimensional shear beam model,the effect was analyzed about dynamic soil pressure on the dynamic shear modulus of the dam foundation soil.The test results show that the amplification effect of acceleration increases linearly from the bottom of the dam foundation to the top dam,and the variation of horizontal earth pressure cannot be ignored in the inverse analysis of shear stress-strain.Besides,the soil shear modulus decreases after considering the effect of horizontal dynamic earth pressure.As the depth increases,the effect of dynamic earth pressure on the shear modulus in the middle of the dam foundation is greater than that of the upper sand layer.Moreover,the relative calculation error increases with the increase of depth and peak acceleration of the input seismic wave.