竖向开挖卸载应力引起的基坑坑底土体变形响应

针对基坑开挖引起的坑底土体和桩基础的回弹变形问题,基于Mindlin解和自重应力抵消法,给出了大面积基坑坑底中心区域的开挖回弹影响深度和回弹变形的计算方法。通过算例计算,对比了基于Mindlin解和基于Boussinesq解的竖向开挖卸载应力、回弹应力分布的区别,指出基于Mindlin解的解答更适用于基坑开挖的情况。研究结果表明：基坑坑底的竖向开挖卸载应力、回弹应力以及回弹影响深度与基坑开挖宽深比、长深比和泊松比正相关；可采用基于Mindlin解的回弹应力的线性分布拟合公式直接计算坑底回弹变形。经上海地区的3个大规模基坑工程实例,验证了本文方法的适用范围和计算精度。

Soil deformation responses to excavation-induced vertical unloading stress in the base of foundation pit

To deal with the excavation-induced rebound deformation of soils and piles in the base of foundation pit, a calculation method for the excavation-induced rebound influence depth and rebound stress in the central base area of large foundation pit, based on the Mindlin solution and the gravity cancellation method. The differences between excavation-induced vertical unloading stress distribution and rebound stress distribution from Mindlin solution and Boussinesq solution are compared from case studies, and the Mindlin solution is more accurate for excavation case. The results show that excavation-induced vertical unloading stress and rebound stress in the base of foundation pit are positive correlated to width - excavation depth ratio, length - excavation depth ratio and Poisson ratio; the linear distribution fitting formula of the rebound stress based on Mindlin solution can be used for the base rebound deformation. The scope of application and calculation accuracy of the suggested method are verified from 3 large-scale foundation pit projects in Shanghai area.