双层堤基上覆层对堤基渗透破坏影响的试验

根据上覆层与下伏砂层的协调变形情况,将上覆层概化为完全不变形的刚性上覆层以及与下伏砂层始终协调变形的柔性上覆层,并利用室内试验对这2种极端情况进行模拟。通过对试验过程中的土体破坏情况、渗透流量、涌砂粒径以及破坏后土体的颗粒组成等方面进行分析,发现具有刚性上覆层的双层堤基在接触面上易形成空洞,而柔性上覆层较刚性上覆层具有更强的抗渗透破坏能力;同时,具有刚性上覆层的堤基发生渗透破坏时粗颗粒更易流失。对渗透破坏过程中的渗流场进行数值模拟,对比了不同渗透破坏阶段的水力梯度分析情况,简要分析造成2组试验差异的原因所在。研究结果表明,使上覆层与下伏砂层保持协调变形是控制渗透破坏发展的有效方法,建议在堤基建设时尽量增加上覆层柔性,使上覆层与下部土体有协调变形的能力。

Effect of superstratum on seepage failure in two-stratum dike foundations

Based on the situation whether or not the superstratum and the underlying sand layer have compatible deformation,the superstratum was conceptualized as the rigid one without deformation and the flexible one with compatible deformation.The two kinds of extreme conditions were simulated by laboratory tests for the seepage failure in two-stratum dike foundations.The soil failure,the seepage discharge,the grain size of piping sands and the composition of eroded soils were analyzed.It was found that cavities easily occurred on the contact surfaces in the two-stratum dike foundation with the rigidity superstratum during the seepage failure.The dike foundations with the flexible superstratum had stronger anti-seepage failure capability.Meanwhile,the grain composition analysis of the piping sands and eroded soils indicated that coarse particles easily drained from the dike foundations with the flexible superstratum during the seepage failure.The seepage fields during the seepage failure were simulated,and the hydraulic gradients at various seepage failure stages.The causes for the difference in tests on the two kinds of superstrata were analyzed.A comparison between the two tests indicated that the compatible deformation of the superstratum and the underlying sand layer could effectively prevent the seepage failure.The flexible superstratum was suggested for the construction of two-stratum dike foundations so as to improve the compatible deformation of the superstratum and the underlying soils.