考虑假想基础宽度的基坑抗隆起稳定性

Basal heave stability of deep excavation considering virtual foundation width

在深厚软土地区,有大量的基坑工程符合下列特征:(1)围护墙插入比为1:2.0~1:2.2;(2)开挖过程顺利;(3)抗隆起安全系数不满足现行相关标准要求。为减少理论与实践之间的不符,基于既有地基承载力模式的计算公式,通过引入假想基础宽度,建立了可考虑土体应力状态和抗剪能力的基坑抗隆起稳定性分析方法。定义了抗隆起安全系数在数学上为最小值的假想基础宽度为临界宽度。除临界宽度外,假想基础宽度的选取还应考虑基坑宽度、软土层厚度等因素。结合已完成工程实例,对比了现有不同稳定分析方法的抗隆起安全系数,分析了软土地层结构、土体内摩擦角等对稳定性的影响。分析结果与实际情况更加接近,且表明土体抗剪能力的影响在采用临界宽度作为假想基础宽度时有限。

In the area of deep soft soil,there are a large number of deep foundation pits conforming to the following characteristics:(1)insertion ratio of retaining wall is between 1:2.0 and 1:2.2;(2)excavation process goes smoothly;(3)basal heave stability does not meet the requirements of relevant standards.In order to reduce the inconsistency between theory and practice,based on the calculation formula of the existed foundation bearing capacity model,a basal heave stability analysis method for foundation pit considering soil stress state and shear capacity was developed by introducing the virtual foundation width.The critical width was defined as the virtual foundation width with the minimal basal heave stability in mathematics.In addition to the critical width,the width of the foundation pit and the thickness of the soft soil layer should also be considered in the selection of the virtual foundation width.A completed engineering example was given to compare the basal heave stabilities of the existed different analysis methods,and to analyze the influence of soft soil layer structure and internal friction angle on stability.The analysis results were closer to the actual situation,and showed that the influence of soil shear capacity was limited when the critical width was used as the virtual foundation width.