深基坑降承压水对墙体变形和地表沉降的影响

Influence of Dewatering in Confined Aquifers on Wall Deformation and Ground Settlements in Deep Excavation

针对深基坑施工引起的环境变形问题,采用流固耦合数值方法,探讨了深基坑降承压水对墙体变形和地表沉降的影响规律.依托工程实例,采用基于Biot固结理论的流固耦合分析方法,通过力学和渗流交替迭代计算模拟开挖降水的耦合作用,并以实测数据验证该方法的合理性.建立三维数值分析模型,对比有无降水条件下基坑的墙体变形和地表沉降,获得深基坑降承压水引起的坑外附加地表沉降曲线,并与相同水位变化下一维固结理论的计算结果对比,探讨两者间的差异及其产生机理.研究结果表明:深基坑降水对墙体变形影响较小,但会明显增大坑外地表总沉降量及其影响范围;基坑降承压水引起的坑外附加地表沉降在墙后1.5倍开挖深度以外,与一维固结理论的计算结果相同;墙土共同作用是导致深基坑降水引起的坑外附加地表沉降在墙后1.5倍开挖深度范围内波动的主要原因.

A numerical method considering the fluid-mechanical interaction is used to study the wall deformation and the ground settlements caused by dewatering in a confined aquifer in deep excavation.In the simulation of project example,the fluid-mechanical interaction methods based on the Biot’s consolidation theory are used to calculate the variation of settlements in deep excavation.Mechanics and seepage are iterated alternately to solve the deformation under combined effect of unloading and dewatering.The rationality of this method is verified by comparing with observed data.The three-dimensional numerical models of deep excavation are established.And the situations with or without dewatering are made direct comparison in terms of dewatering-induced wall deformations and ground surface settlements.By stripping the correlation curve of dewatering-induced additional settlements outside the pit,this paper focus on its discrepancies and mechanism with the comparison of one-dimensional consolidation theory based on the same pore pressure change.The results show that dewatering in the confined aquifer has less effects on wall deformation,but intensifies the magnitude and the influence range of total ground surface settlements.The dewatering-induced additional ground surface settlements outside 1.5 times of excavation depth of the pit match well with the settlements of one-dimensional consolidation theory,while the settlements discrepancy within 1.5 times of excavation depth behind the wall is mainly attributed to the soil-wall interaction.