软土层对地铁狭长深基坑地表沉降的影响研究

随着我国城市轨道交通的快速发展,地铁地下车站狭长深基坑工程越来越多,尤其是长江中下游和沿海地区城市的狭长深基坑大多开挖于深厚软土场地,对该类深基坑的施工安全造成了严重的威胁和工程事故。鉴于此,本文基于Midas商用软件,建立了土体-围护结构相互作用体系的三维有限元分析模型,通过现场实测与数值计算结果的对比分析,验证了数值分析模型的可行性。通过改变软土层厚度、埋深和开挖深度等不同组合的108个计算工况,系统分析了软土层厚度和埋深变化对地铁狭长深基坑周围地表沉降的影响规律。结果表明:当软土层主要位于基坑底面以上侧向地基中时,软土层厚度变化对基坑周围地表沉降影响较大;地铁狭长深基坑侧向地基中软土层埋深增大时基坑周围地表沉降先变大后变小,且变化转折点为软土层顶层埋深高于基坑底面以上的一定范围内;当软土层埋深较大且较厚时,开挖深度对地表沉降的影响有增速的趋势,即当基坑开挖深度较深时软土层的影响更为明显。同时,根据数值计算结果,给出了软土层厚度和埋深等与地表沉降的统计关系。

Effects of Soft Soil Layer on the Ground Settlement of a Long-narrow Deep Excavated Foundation Pit for Subway Station

With the rapid development of the rail transit in China, the number of long and narrow deep foundation pits for the subway stations are increasing fast. Particularly the long-narrow deep foundation pits along the Middle-lower Yangtze River and the coastal line are mostly excavated in the deep soft soil layer, which has caused a serious threat to the safety of the deep excavated foundation pits. Accordingly, by using the Midas software, a three-dimensional finite element model was established to simulate the soil and retaining structure interaction system. Firstly, by comparing the on-site measured results with the numerical modelling, the accuracy of the numerical calculation model was verified. Then, by the 108 calculation conditions, the effect of the soft soil thickness and buried depth were analyzed to the ground surface settlement of the long-narrow deep foundation pit. The results show that when the soft soil layer is mainly located in the lateral foundation above the pit bottom, the changes of the soft soil thickness have great influence on the around ground surface settlement of the foundation pit. When increasing the soft soil buried depth the ground surface settlement of the foundation pit is first increasing and then decreasing. As a result, the turning point for the above change law is located in a certain range above the bottom of the foundation pit. When the depth of soft soil layer is larger and thicker enough, the excavation depth has a greater impact on the around ground surface subsidence. What’s more, the effect of the excavation depth is more obvious when it is larger enough. At the same time, according to the numerical modelling, the statistical relationships among the thickness, the depth of the soft soil layer and the surface settlement, is also given