Research On Slope Stability Evolution Rule Of Soil Damage Caused By Internal Erosion

In the field of geotechnical engineering,engineering problems such as dam breaks and natural disasters such as landslides have always been the focus of attention.Internal erosion is one of the main reasons for dam breaks or landslides.The skeleton of the soil is composed of coarse particles with a larger particle size,and the pores between the coarse particles are filled with fine particles with smaller particle sizes.During the process of seepage,the phenomenon by which the fine particles in the soil will detach from the framework and migrate with the pore water flow is called internal erosion.As internal erosion continues,more and more fine particles are washed out of the soil,forming a dominant channel between the skeleton particles,resulting in the growth of porosity and seepage rate in the soil,and contact between coarse particles in local areas is lost.With the loss of filling fine particles,the bearing capacity of the skeleton will,therefore,gradually decrease,eventually leading to dam break or landslide.Therefore,it is of great practical significance to study the mechanism and characteristics of internal erosion for early warning and treatment of slope stability damage that could lead to disasters like dam breaks and landslides,and to reduce the loss of life and property caused by such disasters.Fine particle loss is one of the most typical characteristics of internal erosion.From a microscopic perspective,fine particle loss causes damage to the soil material to a certain extent.During each of the five stages of internal erosion: initiation,persistence,development,termination and destruction,due to damage effects such as rearrangement and distribution of coarse and fine particles,generation of dominant flow paths(fractures),and changes in porosity throughout the internal erosion process,the geometric structure and mechanical properties of the soil are changing.The governing equation of particle loss considering internal erosion is derived based on Darcy's law,the continuity equation of percolation and the theory of mass conservation.Starting from the change of porosity during the internal erosion process,the damage variable evolution equation characterized by porosity is established to reasonably construct the damage constitutive relationship.COMSOL Multiphysics is used to establish a finite element analysis model for Xiapa landslides.The soil damage caused by internal erosion and its impact on the safety and stability of the slope are analyzed.The main results are as follows:(1)Derivation of seepage control equation considering particle loss characteristics.Based on the law of conservation of mass,the soil particles in the soil are divided into fine particles that can be eroded,fine particles that can be eroded but are not eroded,coarse particles that are not eroded,and pore fluids.The mass conservation equations of these particle phases are derived respectively,so as to establish the governing equations of fine particle loss under internal erosion.Combined with the seepage continuity equation,the coupling relationship between seepage and fine particle loss was established.(2)A damage variable and damage evolution equation of soil considering the change of porosity are established.Based on the damage theory,a meso-damage variable characterized by porosity is selected,and a linear damage evolution equation is established based on the effect of the porosity on the microstructure of the soil.Based on the equivalent principle of elastic residual energy,the constitutive relationship of soil considering damage is established.(3)The calculation method of the safety factor considering the soil damage caused by internal erosion is established.Summarizing the common methods of slope stability analysis.Based on the definition of safety stability coefficient in vector sum method,the calculation formula of safety coefficient is deduced.Calculating the direction of overall slope slide in plane problem and three-dimensional problem.According to the damage constitutive relation,the stress considering the damage of the sliding crack surface is determined.In the vector sum method,the normal stress and shear stress acting on the bedrock of the sliding body are used to replace the normal stress and shear stress without regard to the damage,and then the formula of vector sum method for calculating the safety factor considering the soil damage caused by internal erosion is obtained.(4)A slope stability model considering damage under internal erosion is established.A numerical model of Xiapa landslide was established,and the finite element method was used to simulate the influence of reservoir water level on the internal erosion parameters.The changing porosity,cohesion,and the influence of damage on the constitutive relationship of soil mass under the action of internal erosion were calculated.A vector sum is used to calculate the slope stability safety coefficient when considering internal erosion and without regard to internal erosion,the change of the damage variable and the influence of the damage on the slope anti-slip stability are revealed.