多层承压水地层深大基坑开挖变形规律研究

Study on deformation law of deep and large foundation pit excavation in multi-layer confined water stratum

结合北京新建次渠站工程,从北京地区地下承压水分布出发,采用数值模拟手段对多层承压水地层深大基坑开挖变形规律进行了研究。通过建立三维数值模型,将承压水地层基坑开挖与普通地层基坑开挖进行对比,分析承压水的存在对地铁车站基坑围护结构、基底和地表变形的影响,并对变形规律进行总结分析。研究表明:承压水的存在使基坑开挖卸荷效应更加明显,围护结构变形、基底隆起和地表变形都有所增大。其中地连墙变形增加了36.7%,基底变形增加了193.4%;与普通基坑开挖不同的是,由于多层承压水的存在,基坑墙顶出现上浮,累计上浮值达18.53mm;在实际施工过程,因地连墙施作引起的地表沉降也应考虑在内;基坑开挖地表变形随着开挖深度增加而不断增大,地表变形呈现出“抛物线”形沉降槽,地表沉降槽的出现位置和沉降影响范围与基坑开挖深度有关;在承压水作用下,最终开挖完成时地表最大沉降出现在距坑边约0.8倍的开挖深度处,在施工前可预估最大沉降点的位置,对附近地下管线和邻近既有结构等进行加固保护。

This paper combines with the new Ciqu station engineering, starting from the distribution of confined groundwater in Beijing area, adopted the numerical simulation, the deformation law of deep and large foundation pit excavation in multi-layer confined water stratum is studied. By establishing a three-dimensional numerical model, the excavation of foundation pit in confined water stratum is compared with that in common stratum, and the influence of confined water on the retaining structure, foundation and surface deformation of foundation pit in metro station is analyzed, and the deformation law is summarized and analyzed. The research shows that the existence of confined water makes the unloading effect of foundation pit excavation more obvious, and the deformation of enclosure structure,basement uplift and surface deformation are increased. Among them, the deformation of the diaphragm wall increased by 36.7% and the base deformation increased by 193.4%. Different from ordinary foundation pit excavation, due to the existence of multi-layer confined water, the wall top of the foundation pit floats up, and the cumulative floating value is 18.53mm. In the actual construction process, the surface settlement caused by the construction of diaphragm wall should also be taken into account. The surface deformation of foundation pit excavation increases with the increase of excavation depth, and the surface de-formation presents a "parabola" shaped settlement trough. The location and influence range of surface settlement trough are related to the excavation depth of foundation pit. Under the ac-tion of confined water, when the final excavation is completed, the maximum surface settle-ment occurs at about 0.8 times the excavation depth from the pit edge. The location of the maximum settlement point can be estimated before construction,and the nearby underground pipelines and adjacent existing structures can be reinforced and protected.