计算基坑抗隆起稳定安全系数的卸荷法

Unloading Method to Calculate Safety Factor of Anti-uplift Stability of Foundation Pit

在分析基坑开挖卸荷条件下引起基坑隆起破坏的动力因素基础上,根据极限平衡理论,建立基坑隆起破坏计算模型的几何边界和荷载边界,提出计算基坑抗隆起稳定安全系数的卸荷法,给出基坑抗隆起稳定安全系数计算式(Kk)。假定规范中应用Prandtl公式计算所得的抗隆起稳定安全系数为Kb,通过对两计算式归一化敏感度分析,发现两式受各因素影响的规律一致,影响基坑抗隆起稳定性的首要因素是土体内摩擦角,围护体插入深度和基坑挖深是主要影响因素,土体粘聚力和土体重度是次要影响因素。根据某基坑工程实例计算分析,本文提出的Kk计算值略小于Kb,有利于评价基坑工程实际安全状况。

On the basis of analyzing the dynamic factors causing the uplift failure of foundation pit under the excavation unloading condition,the geometric boundary and load boundary of calculation model for uplift failure of foundation pit are established according to the limit equilibrium theory.The unloading method to calculate the safety factor of anti-uplift stability of foundation pit is proposed.The formula for calculating the safety factor(Kk)of anti-uplift stability of foundation pit is given.It is assumed that the safety factor of the anti-uplift stability calculated by Prandtl formula in the code is Kb.Through the normalized sensitivity analysis of two formulas,it is found that the laws of the two formulas are consistent under the influence of various factors.The primary factor affecting the anti-uplift stability of foundation pit is the internal friction angle of soil.The insertion depth of supporting body and the excavation depth of foundation pit are the main factors.The cohesion of soil and the weight of soil are secondary influencing factors.According to the calculation and analysis of a foundation pit engineering example,the calculated value of Kk proposed is slightly litter than Kb,which is beneficial to evaluate the actual safety situation of foundation pit engineering.