Study On The Mechanism Of Cooperative Slope Protection Of Vegetation Group Roots Under Rainfall Conditions

Vegetation slope protection is one of the main measures used to control landslides.Currently,the commonly used research methods for vegetation slope protection are model testing and finite element numerical simulation.Compared to finite element method,discrete element method has significant advantages in simulating large-scale deformation and damage.Therefore,this paper studies the mechanism of vegetation root slope protection under rainfall conditions from two parts: indoor experiments and discrete element numerical simulation.Firstly,the mechanism of root slope protection was revealed through the root soil composite triaxial test;Then,the discrete element method is used to establish a numerical model of triaxial tests with roots,analyze the shear process of triaxial tests,and calibrate the particle mesoscopic parameters in combination with indoor triaxial tests;Finally,based on the calibrated particle parameters,a numerical model of slope with roots under rainfall conditions is established to study the effects of root content,root inclination,and slope angle on slope stability under rainfall conditions,and to explore the mechanism of vegetation root slope protection.The main conclusions are as follows:(1)Root content has a significant impact on the shear strength of soil,and the presence of roots can increase the shear strength of soil,thereby strengthening the slope.Under low confining pressure,the root system has a significant effect on enhancing the shear strength of soil.With the increase of root content,the cohesion of soil gradually increases,while the internal friction angle of soil is almost not affected by the root content.(2)The peak strength under different confining pressures is positively correlated with contact modulus and friction coefficient,and negatively correlated with stiffness ratio and porosity.In general,the influence on peak strength is ranked as contact modulus>friction coefficient>porosity>stiffness ratio.In terms of elastic modulus,contact modulus>stiffness ratio>friction coefficient>porosity.(3)The PFC-COMSOL coupling method was used to simulate rainfall erosion,and the effects of root content,root inclination,and slope angle on slope stability were studied.The results show that under rainfall conditions,the greater the slope,the worse the slope stability;The higher the root content,the better the slope stability;The slope with vertical root distribution has the best stability,followed by the slope with random distribution,and the slope with horizontal distribution has the worst stability.(4)Analyzing the mechanism of root reinforcement in slope stabilization from the perspectives of displacement field,force chain diagram,porosity,etc.,the root system plays a reinforcing role in the surface soil particles,making the soil cohesion increase,and the force chain become dense and thick,enhancing the shear strength of the slope,thereby improving the stability of the area where the slope is located;The contact model between root particles and soil particles provides a bonding effect.The close bonding between root particles and soil particles reduces the porosity between particles in the fluid grid,and improves the bonding force between the two.The presence of bonding force can increase the sliding resistance of the slope,making the slope less prone to landslides,and exerting the slope reinforcement effect of the root system.