Study On Movement Characteristics Of Group Collapses In Limestone Area

Limestone distributes over a large area in the Three Gorges Reservoir area,and its structural plane is well developed.The steep and high slopes are liable to form dangerous rock masses.The movement of group collapses has the characteristics of large volume,high speed and long distance movement.It has been concerned by scientific researchers and engineers for a long time,but the disasters are still ongoing.For example,in 2009,a large-scale mass collapse occurred in Jiwei Mountain,Wulong County,Chongqing,causing huge casualties and property losses.In order to reduce the impact of collapse disasters on human and property and accelerate the development of national disaster prevention and mitigation projects,it is particularly important to study the characteristics and laws of collapse movement of mass collapses.In this paper,by means of force balance principle,indoor air cushion effect test and simulation test,combined with the example of Jiweishan Group Collapse,the disintegration and movement characteristics of Group Collapse are studied.The results are as follows:1.Regardless of the interaction between rockfall and mass collapse,Rocfall software is used to simulate the large-scale individual rockfall in mass distribution under different working conditions.The results show that:1)slope angle,tangential recovery coefficient and normal recovery coefficient have a greater impact on the rockfall motion state,while friction angle has a smaller impact on it;2)Combining with an example,the rockfall motion state is roughly the same.It can be divided into:initial motion state,flight motion state,collision motion state and sliding friction motion state.Different motion states have different effects on the motion characteristics of rockfall.3)By simulating rockfall of different mass,the probability of impact of rockfall on schools and highways on the slope is 100%.2.Combining with the existing literature at home and abroad,the friction coefficient between the collapse body and the breaking surface will decrease under the influence of air cushion effect,and lubricate the collapse body,so that the movement speed and distance of the group distribution collapse body will be greater,and the friction reduction coefficient is deduced.In order to explore the influence of air cushion effect,the air cushion effect of V-shaped trough with U-shaped trough and different angles was explored through indoor experiments,and the support force of air cushion effect was obtained.Comparing V-shaped trough with V-shaped trough with different angles,it can be seen that at the same height,the larger the volume of lower trough,the more gas trapped,the greater the air compression force formed,and the trap gas.The greater the reaction force of the body to the upper falling object.By comparing V-shaped valley with U-shaped valley,it can be seen that the trapped gas effect of U-shaped Valley is less obvious than that of V-shaped valley.At the same height,although the volume of U-shaped Valley chamber is larger,the air compression force formed by U-shaped Valley is less than that of V-shaped valley.This is because U-shaped Valley is more conducive to air leakage.3.Using the discrete element software PFC^2D,the whole process of disintegration and movement of Jiwei Mountain mass collapse is simulated.The results show that:1)The disintegration of Jiwei Mountain belongs to a continuous process.Firstly,under the action of self-weight,it moves forward as a whole,and produces slip surface and rear edge cracks.Then,under the action of tension,it disintegrates continuously,and disintegrates sufficiently in a very short time,showing debris flow direction.2)From the simulation results,it is easier for the monitoring particles on the upper front to obtain larger velocity and move farther because of the influence of the overhead surface,while the displacement and velocity of the rear particles are relatively smaller because of the influence of the front particles.The movement path of the collapse body is about 2100m long,and the longest movement distance of the monitoring particles is about 1300m.3)Because of the influence of the scraping area on the lower part,the collapse and slide body is affected by the scraping area.The final accumulation volume is much larger than the actual collapse volume,which enlarges the impact degree,and the accumulation length is about 1000m.4.The experiment simulates the movement characteristics of the collapse body under different friction coefficients.The results show that:1)the smaller the friction coefficient,the farther the movement velocity and distance of the collapse body are,and the greater the degree of bond rupture of the particles,the less the residual bond;2)When the friction reduction coefficient is 0.8,that is,the friction coefficient is 0.291,the simulation of the movement characteristics of the collapse body is more consistent with the actual situation.