地下水位波动下基坑周围地基土的孔压响应半解析解

Semi-analytical solution of pore pressure response around excavations to groundwater level fluctuation

水位波动条件下的基坑性状研究是随工程实践产生的新课题,而基坑周围的孔压响应机制是该课题的关键问题。将基坑渗流场分区,假设土体总应力不变,将固结方程解耦,利用Laplace、Fourier变换推导了浅层含水层内地下水位波动时板式支护基坑周围地基土孔压响应的二维近似半解析解。利用该解答,对综合系数θ(与土体固结系数、海床厚度、水位波动周期相关)、孔隙流体压缩系数与围护墙插入深度的影响进行分析。结果表明:孔压波动幅值沿基坑最短渗流路径不断衰减,滞后相位不断增大;θ越大,基坑周围地基土的相对孔压波动幅值越小,滞后相位越大,稳态渗流时的相对孔压为地下水位波动条件下不同θ值相对孔压波动幅值的极大值;孔隙流体压缩系数越大,基坑周围的波动孔压响应幅值越小,滞后相位越大;围护墙插入深度越大,主动侧相对超孔压波动幅值越大,被动侧波动幅值则越小。

The behavior of excavations subjected to water fluctuation is a new subject in engineering practices, with the pore pressure response around them being the focus. By dividing the seepage area around the excavations into several zones and assuming the total stress constant, the consolidation equation is decoupled, and then a semi-analytical solution of pore pressure response around a plate-supported excavation to water level fluctuation is deduced in conjunction with the Laplace and Fourier transformations. Based on the above solution, a parametric study is carried out to examine the effects of comprehensive coefficient θ (related to consolidation coefficient, seabed thickness and period) and compressibility of pore fluid on the pore pressure response. The results indicate that the amplitude of the relative pore pressure attenuates along the shortest seepage path, while the phase lag increases accordingly. The larger theθ, the smaller the amplitude of relative pore pressure and the larger the phase lag;furthermore, the maximum amplitude equals the value of the relative pore pressure in steady condition. In addition, the larger the compressibility of pore fluid, the smaller the amplitude of excess pore pressure and the larger the phase lag. The larger the embedded depth of retaining wall, the larger the amplitude of pore pressure in active side and the smaller the amplitude of pore pressure in passive side.