动态承压水作用下考虑土体非线性的基坑弱透水层出逸比降研究

Analysis on exit gradient of aquitard at bottom of foundation pit under dynamic confined water considering nonlinearity of soil

针对滨海临江地区基坑底部弱透水层由动态承压水导致的突涌问题,将基坑底部弱透水层渗流问题简化为一维越流模型,考虑土体的压缩非线性和渗透非线性,推导动态承压水作用下弱透水层超静孔压半解析解,通过与有限差分解进行对比,验证解的可靠性.分析土体非线性以及动态承压水参数对弱透水层中超静孔压和开挖面处出逸比降的影响.分析结果表明:当考虑土体的非线性特性时,弱透水层中各深度处的超静孔压均大于线性假定下的结果;承压水波动过程中基坑开挖面处最大出逸比降随无量纲因子的增加而增加;不考虑土的非线性会使求得的出逸比降偏小.用线性假定下的解进行突涌稳定性分析或者降水设计均会带来较大的安全隐患,在动态承压水变化周期长、平均水位高、波动幅值大的情况下应充分考虑土体非线性的影响.

Aiming at the problem that the confined water usually fluctuates in coastal area and it will cause inrush accidents of foundation pit.To deal with the stability in this condition,the seepage consolidation theory was used.Then the semi-analytical solution of excess pore water pressure considering soil nonlinearity was deduced.The solution was compared with the results by finite difference method in order to verify the validity of the solution.The effects of soil nonlinearity and dynamic confined water parameters on the excess pore pressure in the aquifer and the exit gradient at the excavation surface were analyzed.The calculating results show that the excess pore pressure considering the nonlinearity of the soil is larger than that under the linear assumption at all depths.The maximum exit gradient at the excavation surface of the foundation pit increases with the increasing of the dimensionless factor.The exit gradient will be smaller without considering the nonlinearity of the soil.The analysis of stability or precipitation design with solutions under linear assumption will lead to great potential safety hazards.The nonlinear influence should be fully considered especially when the dynamic pressure water has a long cycle of change,the average water level is high,or the amplitude of the fluctuation is large.