软土地区坑中坑的抗隆起稳定性分析

Stability Analysis of Pit-in-Pit against Upheaval in Soft Soil Area

借助基于强度折减法的有限元模型,分析坑中坑隆起失稳形式。由计算结果可知:坑中坑的隆起失稳形式与内外坑间距密切相关;当内外坑间距小于外坑最下道支撑点至外坑围护结构底的距离时,坑中坑隆起失稳时墙底滑裂面为以外坑最下道支撑与内外坑间某位置的交点为圆心、并通过内外坑围护结构底以下某点的圆弧面;当间距大于该距离时,坑中坑对隆起失稳形式无影响,可按单一基坑来计算。在此基础上,利用极限平衡分析法推导出坑中坑抗隆起稳定安全系数的计算公式。以上海市自然博物馆与地铁13号线共建工程为背景,计算不同工况下坑中坑的抗隆起稳定安全系数。由计算结果可知:当内外坑间距小于20m时,坑中坑可能发生隆起失稳破坏,需对内外坑间的土体进行加固处理。

With the finite element model based on strength reduction, the upheaval buckling forms of pit-in-pit were analysed. We can see from the calculation results that the buckling forms of pit-in-pit are close- ly related to the distance between inside and outside pits. When the distance between inside and outside pits is less than the distance between the bottom support point and bottom enclosing structure of outside pit, the bottom slip surface upon pit-in-pit upheaval buckling is an are surface with the intersection be- tween the bottom support of outside pit and a certain position between inside pit and outside pit as the cen- ter, and passing through a certain point under the enclosing structure of inside and outside pits. When the distance between inside and outside pits is greater, the pit-in-pit has no effect on upheaval buckling forms, which can be considered as a single foundation pit. On this basis, a calculation formula for the safety factor of pit-in-pit against upheaval was derived based on limit equilibrium analysis method. With the joint con- struction engineering of Shanghai Natural Museum and Metro Line 13 as background, the safety factors of pit-in-pit against upheaval were calculated under different working conditions. Calculation results show that when the distance between inside and outside pits is less than 20 m, upheaval buckling failure may oc- cur to pit-in-pit, and the soil mass between inside and outside pits should be reinforced.