基于随机场理论的基坑开挖地表及围护墙变形分析

Deformation analysis of surface and retaining wall induced by braced excavation based on random field theory

针对基坑开挖引起地表及墙体变形方面的问题,以小应变模型为出发点,采用随机场理论和数值计算相结合的方法,研究土体刚度参数空间变异性对黏土基坑墙后地表沉降和围护墙侧移变形规律的影响。利用协方差矩阵分解法建立参数各向同性随机场模型,结合Monte-Carlo策略,分析黏土刚度的波动距离和变异系数对地表及墙体变形的影响规律。研究结果表明:黏土刚度空间变异性对基坑开挖引起的变形规律有着重要的影响;当波动距离与基坑开挖尺寸接近时,地表沉降结果和最大变形比值最为离散,而围护墙侧移结果则没有出现类似的现象;低刚度占优效应使地表最大沉降均值和围护墙最大侧移均值在随机分析(与确定性结果相比)中呈现出不同的规律。借助概率统计的方法,研究地表沉降和围护墙侧移变形超出监测控制值的可能性,可以为基坑开挖引起最大变形的安全预警提供参考。

Based on the small strain model,the random field theory is combined with the finite analysis method to study the influence of the spatial variability of stiffness parameters on the surface and retaining wall deformation induced by braced excavation.A series of isotropy random field models of clay stiffness are generated by Covariance Matrix Decomposition method.With Monte-Carlo framework,the paper analyzes the influence of coefficients of variation and scales of fluctuation on the surface settlement and retaining wall deflection.The results show that the spatial variability of stiffness parameters in clay has an important influence on surface settlement and retaining wall deflection.The surface settlement and the maximum deformation ratio are the most dispersed when the scales of fluctuation is close to the excavation size while similar conclusion has not been drawn in retaining wall deflection.Compared with the corresponding deterministic results,the mean values of maximum surface settlement and maximum retaining wall deflection show different results in the stochastic analysis because of the dominant effect of low stiffness.With the help of probability statistics method,the paper studies the possibility of surface settlement and retaining wall deflection exceeding the monitoring control values,which can provide a reference for the safety warning for the maximum deformation induced by braced excavation before construction.