考虑土体吸力基坑抗隆起稳定性极限上限分析

Upper Limit Analysis on Basal Heave Stability Considering Soil Suction stress

软土及高水位地区基坑降水对土体抗剪强度及基坑稳定性有积极作用。基于有效饱和度和土-水特性参数的非饱和吸应力模型,推导了地下水位面以上土体吸应力的空间分布规律。在此基础上,假设基坑地连墙与土体之间部分粗糙,考虑土体吸应力引起的土体内能耗散,基于塑性极限分析上限定理采用Terzaghi机构推导了基坑抗隆起稳定性的上限解。对比分析了考虑降水与不考虑降水时基坑抗隆起稳定性的差异,研究了基坑降水条件下坑底抗隆起稳定性与基坑深度、地下水位以及土体内摩擦角,进气值等因素的关系。研究结果表明,在降水条件下,水位线以上土体基质吸力提高,土体抗剪强度增加,基坑抗隆起稳定性随降水深度的增加而显著提高,基坑抗隆起稳定性随基坑开挖深度的增加而降低。研究结果为基坑降水施工过程中的抗隆起稳定性分析提供了一定的理论依据。

In soft soil and high water level area,the foundation pit’s dewatering has a positive effect on the shear strength and the stability of the foundation pit.Based on the effective saturation and soil-water characteristic parameters,the spatial distribution of the soil suction stress above the groundwater level was deduced.On this basis,assuming that the friction between the wall and the soil was partial rough,considering the energy dissipation of the soil caused by the soil suction stress,based on the plastic limit analysis of the upper limit,the upper bound solution of stability of foundation pit was derived by Terzaghi mechanism.The basal heave stability of foundation pit under the condition of dewatering and without dewatering was compared.The relationship between the stability of foundation pit and the depth of foundation pit,the change of groundwater level,the friction angle of soil and the air-entry pressure in the foundation pit was studied.The results show that,under the foundation pit’s dewatering,the soil suction stress and the stress strength above groundwater level increase,the basal heave stability of foundation pit increases with the increase of dewatering depth,the bigger friction angle of soil is beneficial to the stability of foundation pit,and the basal heave stability of foundation pit is accompanied with the decrease of foundation pit depth.The results provide a scientific basis for study the basal heave stability of a foundation pit.