空间效应下狭长深基坑地表三维变形预测

Prediction of three-dimensional surface deformation of long and narrow deep foundation pit under spatial effect

为预测空间效应影响下狭长深基坑开挖引起的周边地表沉降,在现有地表沉降二维平面计算方法基础上,引入k值定量描述空间效应影响,推导出空间效应影响下狭长深基坑周边地表沉降的三维预测计算方法.采用数值计算方法,分别研究了基坑尺寸、土体内摩擦角、围护结构刚度对k值的影响,并给出k值的拟合计算公式.以北京地铁7号线万盛南街西口站深基坑工程为背景,计算分析了基坑周边地表三维沉降变形数值.结果表明:空间效应影响范围主要受基坑开挖深度及土体内摩擦角影响;在空间效应范围外,k值可近似为1,在空间效应范围内,k值随着距基坑端部距离增大呈非线性增长;地表沉降二维计算值相较三维计算结果偏大,地表沉降三维计算结果和实测值较为吻合.

Base on the existing two-dimensional method, a three-dimensional prediction method of ground subsidence around a long and narrow deep foundation pit was proposed. And the parameter k was used in this method to quantitative analysis of the spatial effect. The effects of the excavation size, soil’s internal frictional angle and the stiffness of the retaining structure on the k value were studied by numerical method respectively and the fitting formula of k value was presented. Taking the deep excavation project of Xikou station of Wansheng South Street of Beijing Metro Line 7 as a background, the three-dimensional ground subsidence around the foundation pit was analyzed. The results show that the influence scope of spatial effect is mainly affected by the excavation depth of foundation pit and soil’s internal frictional angle. The k value can be taken as 1 if it’s out of range of spatial effect. It increases nonlinearly with the increase of the distance from the end of foundation pit in the range of spatial effect. The calculated values of three-dimensional ground subsidence are smaller than that of two-dimensional and are closer to the site monitoring date.