二元堤基结构堤防管涌机理模型试验

为了科学解释二元堤基结构堤防管涌致灾机制并揭示其形成、演化过程和致溃规律,在考虑堤基强、弱透水层之间壤土过渡层作用的基础上,通过室内模型试验完整地模拟了二元堤基管涌从单个泡泉发展至管涌群并最终造成堤基塌陷溃决的全过程。试验结果表明:上部黏土及壤土层在渗流的顶托作用下向上隆起并在堤基内部产生层间水平渗漏通道,导致发生潜层砂沸,最终向上发展为表面砂沸的渗透破坏；二元堤基结构管涌发展可分为裂缝发展、潜层破坏、上覆层破坏、管涌通道上溯、堤基破坏和堤基溃决6个发展阶段；表面砂沸由潜层砂沸发展而来,潜层砂沸是由于土层内竖向坡降所引起的渗流力大于上部土体浮容重时造成的土层结构破坏所致,临界竖向坡降处于0.9~1之间；壤土层的存在会加快堤后自由边界区域管涌群的发展速度,但可以延缓管涌通道的上溯,对堤基具有保护作用。

Model test study on piping mechanism of binary dike foundation structure

To scientifically explain the mechanism of piping disaster and reveal its formation, evolution process and burst law on the basis of considering the action of loam transition layer between the strong and weak permeable layers of dike foundation, the whole process of piping of a binary dike foundation structure from single bubble spring to piping group and finally resulting in collapse of dike foundation was completely simulated by indoor model test. The results show that the overlying soil layer uplifts upward under the jacking effect of seepage and produces horizontal channels between layers inside the dike foundation, leading to submerged sand boiling and eventually develops upward to the seepage failure of surface sand boiling. The piping development of binary dike foundation structure can be divided into six stages, including crack development, latent layer failure, overlay damage, upward development of piping channel, damage of dike foundation and dike break.The surface sand boiling is developed from the submerged sand boiling. The submerged sand boiling is caused by the damage of the soil structure induced by the seepage force due to the vertical slope in the soil layer greater than the floating bulk density of the upper soil. The critical vertical slope is between 0.9 and 1. The existence of loam layer accelerates the development of piping group in the free boundary area behind the dike, but it can delay the upstream of piping channel and protect the dike foundation.