开挖前降水作用下基坑围挡结构-地层相互作用机制

Interaction mechanism between retaining wall and soil under pre-excavation dewatering

依托天津地铁3号线某车站基坑实测资料,建立二维流固耦合有限元数值模型,研究不同基坑宽度和开挖前降水深度条件下被动区土压力、地基土水平向基床系数等参数沿深度的分布规律,并将数值分析结果与传统基坑设计中基于m法得到的结果进行对比和分析。结果表明,基坑开挖前降水时,降水深度范围内的地基土水平向基床系数相较于m法确定的值有较大幅度减小,并且基坑宽度和降水深度越大,地基土水平向基床系数就越小。这是由于降水过程中降水井旁渗流力的作用导致被动区土体发生背离围挡结构的水平位移,并进一步引起复杂的围挡结构-土相互作用。利用弹性地基梁法进行开挖前降水引发基坑围挡结构变形预测时,若采用m法来确定地基土水平向基床系数,将会低估开挖前降水引发的围挡结构变形。

In this study,a 2D fluid-solid-coupled numerical model was established based on the investigation data of a station of Tianjin metro line 3,and a series of numerical simulations were carried out to investigate the distribution of horizontal foundation modulus along the depth under conditions of different foundation pit width and dewatering depth.The numerical results are compared with those computed by the m method,which is a traditional design method of foundation pit recommended in the Chinese Code.The results indicate that under the common conditions of pre-excavation dewatering(PED),the horizontal foundation modulus decreases greatly compared with the values determined by the m method,and the larger the pit width and dewatering depth,the greater the decrease extent.When using the elastic foundation beam method to predict the PED-induced deformation of a retaining structure,the obtained deformation will be underestimated,if the m method is used to determine the horizontal foundation modulus.