Numerical investigation of characteristics and mechanism of tunnel erosion of loess with coupled CFD and DEM method

Abstract

Tunnel erosion of loess can cause geological disasters such as landslide and debris flow, as well as threaten the safety of civil engineering structures. Understanding the mechanism and evolution law of tunnel erosion is not only helpful to analyze the occurrence and development of gully erosion, but also conducive to the guidance of engineering practice. Although many scholars have carried out statistical analysis on loess tunnel erosion based on field investigation, quantitative analysis and visualization at the micro level are lacking. Because the combination of computational fluid dynamics (CFD) and discrete element method (DEM) has great advantages in studying the seepage erosion process. This manuscript adopts the CFD-DEM coupling method, and the virtual cement method is used to transform the failure of cemented matrix into the reduction law of bonding strength. The micro mechanism of tunnel erosion of three areas is discussed from the aspects of particle erosion rate, cement evolution and micro mechanical field. The results show that the more the fine particle content is, the greater the cementation is, the stronger the erosion resistance is, the less developed the erosion rate of the particles is, and the dissolution failure rate of the cement is usually earlier than the erosion rate of the particles, and the variation range of the anisotropy of the contact force is also the smallest. However, under high water pressure, their erosion rates are almost synchronous and reach the slow erosion stage quickly. The anisotropic parameters of the contact force of the three samples virtually decreased gradually in the process of erosion, and finally tended to be stable.