地下水渗流对悬挂式止水帷幕基坑变形影响

摘要

以某透水性土层较深的悬挂式止水帷幕基坑为背景，采用ABAQUS建立考虑分级降水开挖全过程的三维流固耦合模型，研究降水对于基坑变形发展的影响规律和不利因素，分析开挖前预降水深度、止水帷幕深度对基坑变形性状的影响. 研究表明：渗流与开挖支护具有明显的耦合效应，降水引起的围护结构侧移增量模式随开挖和支撑施作情况不同而差异较大，降水引起的地表沉降是由土体固结和渗流引起的围护结构侧移引发的地表沉降组成；地表沉降影响范围较经验预测值明显偏大，在基坑西侧地表沉降最大点，降水施工期累积产生的沉降约占48%；各级降水中第1级降水对基坑变形最不利，围护结构初始侧移随第1级降水深度的增加而快速增长，使得竣工后的最大围护结构侧移和坑外地表沉降呈指数增长；止水帷幕对于减少坑外水位下降和控制地表沉降有显著作用，随着帷幕深度的增加，地表最大沉降和沉降影响范围降低，存在最优止水帷幕深度使得帷幕超过最优深度后地表沉降趋于稳定.%Taking the deep foundation pit with a suspended impervious curtain as an example, ABAQUS was used to establish the three-dimensional fluid-solid coupling model considering the whole process of grading precipitation and excavation in order to analyze the influence and unfavorable factors of precipitation on the deformation of the foundation pit. Then the depth of first-stage precipitation and the impervious curtain were analyzed. Results show that seepage and excavation support have coupling effects. The lateral displacement increment of support piles caused by precipitation varies with the conditions of excavation support. The ground settlement caused by precipitation is influenced by soil consolidation and the lateral displacement of support piles caused by precipitation. The scope of ground settlement is larger than that of empirical prediction, and precipitation-induced settlement accounts for 48% at the maximum point of settlement. The first-stage precipitation is the most unfavorable to the foundation pit of all stages of precipitation. The initial lateral displacement of support piles increases rapidly with the increase of the first-stage precipitation depth, so that the growth of the final maximum lateral displacement of support piles and ground settlement is exponential. The impervious curtain can effectively reduce the water level outside the foundation pit drop and control ground settlement. The maximum ground settlement and the scope of ground settlement decrease as the depth of the impervious curtain increases. There is an optimal curtain depth which makes ground settlement stabilize after the curtain depth exceeds the optimal depth.