砂土覆盖岩溶地层基坑开挖引起地层变形分析

Strata Deformation Behaviors Analysis Caused by Deep Excavation of A Metro Station in Sand Covered Karst Strata

广州地层上部为松散的砂性土与粘性土沉积地层,软土层下面则存在较多的石灰岩地层,岩溶分布广泛,溶洞内含大量泥砂与岩溶水。本研究针对广州这种浅埋岩溶强烈发育的上软下硬地层的特殊性,建立了广州市花都区地铁车站工程基坑开挖的有限元模型,考虑开挖过程、围护结构和土的共同作用以及时间等因素的影响,实现对开挖、支撑装拆的动态模拟,结合工程实际监测数据,综合分析围护结构的内力、变形及开挖引起的环境效应。数值模拟结果符合实际工程情况和规范要求。结果表明,土体沉降及侧向位移随开挖过程增大。开挖结束后,土体沉降与地下连续墙侧移范围均在规范的控制范围之内。说明本工程所采用的基坑开挖设计方案满足要求,很好地实现了对周边环境影响的有效控制。所以,本文得出的结论适用于广州地区类似基坑工程的变形预测和优化设计。

The quaternary deposit in Guangzhou City is soft soil composed of loose sand and clay.Limestone stratum with karst is widely distributed under soft soil.Karst caves are filled with large quantity of silt and water.A finite element model was established to simulate the excavation of a deep foundation pit in Guangzhou,which is constructed on these upper-soft-lower-hard strata.The entire building envelope was seen as a structural system in the numerical simulation method.Considering the interaction of excavation process,retaining structures and soil,the dynamic simulation of construction progressively excavation and support system assembling and disassembling was conducted.The environmental effects caused by the internal forces and deformation of retaining structures and excavation were also analyzed.Results of the numerical simulation are similar to the actual engineering situation.The results indicate that ground subsidence increases with the excavation progressed.After excavation,ground subsidence and lateral displacement of diaphragm wall are both in the control range of the specification limit.The excavation plan of this project met the requirements very well and the impact on the surrounding environment due to the excavation was effectively controlled.So the conclusions can be used for the deformation prediction and the design optimization of similar foundation pit in Guangzhou City.