土石混合体渗透侵蚀特性数值模拟研究

Numerical simulation of internal erosion characteristics of block in matrix soil aggregate

土石混合体是由块石、砾石与砂土、黏土等固体颗粒组成,以块石镶嵌在细粒土体中为结构特征的松散介质。由于其颗粒松散特性,细颗粒在渗流作用下易于流失而形成渗流侵蚀。采用室内试验与数值模拟相结合的方法,扩展渗流侵蚀模型在土石混合体渗透侵蚀研究中的应用。选取云南某滑坡土石混合体为研究对象,采用自制的渗透侵蚀装置,模拟土体基质渗透侵蚀过程,获取土体基质侵蚀参数试验值。根据块石在土体基质中分布特征,建立不同块石含量特征的土石混合体计算模型。基于参数试验值及渗流侵蚀方程、耦合渗流控制方程及孔隙率控制方程,模拟土石混合体渗流侵蚀过程,分析块石含量对土石混合体渗透侵蚀特性的影响。模拟结果表明:在同等水力梯度及时间条件下,块石含量与土石混合体宏观平均流速初值、侵蚀颗粒密度值呈反比,与液化颗粒密度峰值呈正比;块石含量与渗流侵蚀方程中试验参数存在线性相关性。将块石含量作为土石混合体结构特征引入渗流侵蚀方程中,以构建适用于土石混合体的渗流侵蚀模型。

Block in matrix（BIM） soil is composed of block stone, gravel, sand, clay and other solid particles. The model for seepage erosion in BIM soil is assumed as the form of Sterpi Formula, and the content of block stone as one of the most important parameters of BIM soil needs to exist in the model. However, due to the complexity of grain sizes in BIM soil and the limitation of traditional experimental setup in the laboratory, it is hard to conduct experiments directly to study seepage erosion in BIM. Therefore, a new method is proposed to obtain these parameters by means of numerical simulation on BIM soil and experiments of seepage erosion on gravel soil matrix without block stones. BIM soil from a landslide in Yunnan Province is selected as an example. Firstly, an experimental setup is designed to perform a series of seepage erosion tests on gravel soil matrix without block stones to obtain its seepage parameters. Then, based on the governing equations of particle migration, coupling seepage and porosity, numerical simulation is carried out to characterize the process of seepage erosion in BIM soil under the assumption of block stones with poor permeability. Numerical results show that when hydraulic gradient and time are consistent, the average initial velocity of BIM soil is inversely proportional to the content of block stone, but the density of liquefied particles is proportion to the content of block stone. Finally, a formula is presented for seepage erosion in BIM soil with the content of block stone as one of parameters.