软土地区隔断墙控制基坑变形的作用机理及其效果研究

以天津软土地区20个地铁车站基坑实测资料为背景,建立地铁车站基坑标准化模型,采用有限元与正交试验相结合的方法,重点研究隔断墙距同侧围护结构的水平距离L、隔断墙的刚度E及其入土深度H 3个主要设计参数对其控制围护结构内力、侧移以及坑外地表沉降的作用。结果表明:3个参数的变化对基坑的变形控制均有不同程度的影响,其中L主要影响围护结构内力及地表最大沉降,最大沉降可减小60%以上;H主要影响围护结构最大侧移,最大可以减小为未设置隔断墙时的50%左右;而E在常规变化范围内对基坑变形的影响相对较弱。其次,通过引入"相似结构"双排桩的计算理论,建立了L与隔断墙分担围护结构内力及土压力间的定量关系。最后利用Kung等基于可靠度理论提出的预测基坑变形的方法分析软土地区隔断墙的控制效果,同时与实测值和有限元计算结果进行对比,验证了上述结论的适用性。

Research on diaphragm wall mechanism and effect of deformation control in soft soil

On the basis of measured data from 20 subway station foundation pits in Tianjin, a normalized model is established and the affection of the distance between diaphragm wall and retaining structure（L）, the stiffness（E）and the depth of diaphragm wall（H） which may influence the internal forces (M_D) and horizontal displacement (δ_hm) of the containment structure and the surface subsidence (δ_vm), are studied by using the finite element method and orthogonal test. And it turns out that the three factors influence the deformation control of foundation pit in varying degrees. L primarily affects M_D and δ_vm, and the maximum settlement can be reduced by more than 60%. And H mainly controls δ_hm, to the greatest extent, the lateral displacement can be reduced by about 50%. But the impact of E is not obvious within the range of normal variation. Then according to the computation theory for the similar structure of double row pile, the quantitative relationship of internal forces between diaphragm wall and containment structure is established. Finally, the applicability of the above conclusions to the deformation control and prediction of foundation pit in soft soil is verified by using the deformation prediction of Kung et al. to analyses the control effect of diaphragm wall in soft soil area, and by comparing with the measured value with the result of the finite element calculation.