深厚软土地区基坑墙底抗隆起稳定性Prandlt计算式的讨论  

A discussion of the Prandlt calculation formula for anti-uplift stability of the bottom of a foundation pit wall in deep soft soil areas

作　　者：阳吉宝 YANG Jibao(Shanghai Municipal Engineering Design Institute(Group)Co.Ltd.,Shanghai 200092,China)

机构地区：[1]上海市政工程设计研究总院(集团)有限公司,上海200092

出　　处：《水文地质工程地质》2021年第2期61-69,共9页Hydrogeology & Engineering Geology

摘　　要：深厚软土地区采用Prandlt公式计算基坑抗隆起稳定性常常不满足规范要求,给基坑支护设计带来较大困惑。本文在分析基坑开挖与Prandlt公式计算地基极限承载力的力学边界条件差异的基础上,指出采用Prandlt计算式、临界宽度法和计入基坑内侧土体抗剪强度等改进计算方法的不足,提出同时考虑基坑支护体内外两侧土体抗剪作用的改进计算公式。通过对4个计算公式各参数的敏感度分析,发现内摩擦角是影响基坑墙底抗隆起稳定性的首要因素,基坑挖深和支护体插入深度是主要影响因素,土体黏聚力是次要影响因素,土体重度的影响可以忽略。软土内摩擦角较小,在基坑挖深一定的条件下,只有通过加大支护体插入深度才能保证基坑墙底抗隆起稳定性,因此,考虑基坑支护体内外两侧土体抗剪强度的有利作用可合理优化基坑支护设计。本文通过工程实例研究,验证了计入基坑支护体内外两侧土体抗剪强度作用的合理性;同时,根据浙江软土地区多项工程墙底抗隆起稳定安全系数计算结果的统计分析,指出目前规范取值标准偏高,在软土地区不尽合理,建议在积累工程经验的基础上,适当降低规范计算方法的标准限值。The Prandlt formula is often used to calculate the anti-uplift stability of foundation pits in deep soft soil areas,which often fails to meet the specification requirements and brings great confusion to the design of foundation pit support.Based on the analysis of the difference in mechanical boundary conditions between the foundation pit excavation and the Prandlt formula for calculating the foundation bearing capacity,this paper points out the shortcomings of the improved calculation methods such as the Prandlt formula,critical width method,and takes into account the shear strength of the soil inside the foundation pit method,and puts forward an improved calculation formula considering the shear effect of the soil inside and outside the foundation pit support.Through sensitivity analysis of each parameter of the four calculation formulas,it is found that the internal friction angle is the most important factor affecting the stability of foundation pit wall bottom against uplift.The excavation depth and the insertion depth of the supporting body are the main influencing factors,the cohesion of soil body is the secondary influencing factor,and the influence of soil weight can be ignored.The friction angle of soft soil is small.Under certain excavation depth,the stability against uplift of foundation pit wall bottom can be guaranteed only by increasing the insertion depth.Therefore,considering the favorable effect of shear strength of soil on the inner and outer sides of foundation pit support,the foundation pit design can be reasonably optimized.This paper also verifies the rationality of taking into account the shear strength effect of soil on the inner and outer sides of the foundation pit support through engineering case studies.At the same time,according to the statistical analyses of wall bottom stability calculation of many projects,it is pointed out that the current standard is too high and unreasonable in soft soil areas.It is suggested that the standard limited value of the standard calculation method sh

关 键 词：软土地区 抗隆起稳定性 Prandlt公式 改进 

分 类 号：TU471.8[建筑科学—结构工程]