恒定围压下间断级配散粒土内部侵蚀机理研究

Study on Internal Erosion Mechanism of Gap-Graded Granular Soil under Constant Confining Pressure

摘要:

管涌侵蚀一直是水力学研究的重点，其是指在渗透水流作用下土体内部细颗粒发生迁移并形成渗漏通道的一种渗漏现象，且在围压条件下土体内部侵蚀过程会受到显著的影响。利用自主研发的应力动态联动式渗透变形试验装置对不同级配的散粒土在恒定围压条件下的侵蚀过程进行研究。设置三组不同的间断级配试样，对渗流过程中的渗流量、细颗粒流失量和渗透变形量进行测量。结果表明：试验前期渗流速度v和水力梯度i呈线性正相关， 但围压作用使得i?v曲线后期明显变缓不再符合达西定律；土体中间级配缺的越多，颗粒起动的临界水力梯度越小； 且土体的不均匀系数对渗透系数的影响存在某一上限值。渗流过程中细颗粒的流失存在因堵塞而引起的自滤自稳定现象，该现象在骨架颗粒级配较为均匀时更易出现。土体在恒定围压条件下细颗粒流失导致体积收缩，而由于土体内部颗粒间的作用力突变，土体渗透变形呈现阶梯状变化，且在土体颗粒级配间断跨度大、内部细颗粒粒径小且单一的情况下阶梯状变化较为明显。

Abstract:

Piping erosion has long been a focus in hydraulics research. It refers to a seepage phenome non where fine particles within the soils migrate under the action of seepage flow, leading to the forma tion of seepage channels. The internal erosion process of the soils is significantly affected by confining pressure. This study investigated the erosion process of granular soils with different gradations under constant confining pressure by using a self-developed stress-dynamic linked seepage deformation ex periment device. Three groups of gap-graded soil samples were prepared to measure the seepage flow, fine particle loss, and seepage deformation during the seepage process. The results showed that at the early stage of the experiment, the seepage velocity (v) and the hydraulic gradient (i) had a linear posi tive correlation, but the confining pressure caused the i-v curve to flatten significantly later on, deviat ing from Darcy's law. The more intermediate gradations the soils lacked, the smaller the critical hy draulic gradient at which particles began to move. Moreover, there was a threshold value for the effect of the soils' nonuniformity coefficient on the permeability coefficient. During the seepage process, the loss of fine particles led to self-filtration and self-stabilization due to clogging, which was more likely to occur when the skeleton particle gradation was relatively uniform. Under constant confining pres sure, the loss of fine particles caused soil volume shrinkage. Due to abrupt changes in the inter-particle forces within the soils, the permeability deformation of the soils exhibited a stepwise change. This stepwise change was particularly pronounced when there was a large gap in the particle gradation of soils and the fine particles were small and uniform in size.