Research On Damage And Disintegration Mechanism Of Wangxia Unstable Rocks In Three Gorges Reservoir Area

In recent years,the number of geological disasters that occur in China each year accounts for about 20% of the total number of geological disasters.The collapse of dangerous rocks is a form of geological disasters with high frequency in the Three Gorges reservoir area.The destruction of dangerous rocks in the limestone region and the danger in sandstone areas The biggest difference in rock failure is that the former destroys often show disintegration.In-depth analysis of the mechanism of damage and disintegration of dangerous rocks in the limestone region is not only the fundamental need for the prevention and control of geological disasters in the Three Gorges Reservoir Area,but also will help to understand the ash more clearly.Movement process of disintegration and collapse of dangerous rock in rock area.Taking Wushan Wangxia dangerous rock as an example,this paper systematically analyzes the damage and disintegration mechanism using limit equilibrium method,fracture mechanics,energy theory,and other research methods,and then analyzes the dangerous rock mass through indoor triaxial tests and finite element numerical simulation.A slippery destruction occurred.The main research results are as follows:(1)The formation of the Wangxia dangerous rock is a long process of geological evolution and is the result of the coupling of multiple factors.Topography and geomorphology and formation lithology constitute an important material basis for the development of dangerous rocks.Under the combined effects of gravity unloading,rainfall,weathering,dissolution and other natural factors and artificial activities of coal mining,large-scale deformation and destruction of the dangerous rock eventually occur.The disaster deduction modes of destruction and disintegration can be summarized into three stages: formation and retreat of steep cliffs,time-dependent deformation of dangerous rock masses,and destruction and disintegration of dangerous rock masses.(2)The geological model and mechanical model of the Wangxia dangerous rock were constructed.The stability factor of dangerous rock under different external loads was solved by mechanics and fracture mechanics.The expression of the stability coefficient of dangerous rock was deduced from the limit equilibrium theory.The stability coefficient of dangerous rocks under different fill heights was analyzed and calculated,and the key factors inducing unstable failure of dangerous rocks were analyzed.(3)Based on fracture mechanics related theory,the basis for the judgment of compound fractures in dangerous rock masses was deduced.The calculated results show that the stress intensity factors I and II at the crack tip of the dangerous rock mass are all greater than zero,indicating that the crack tip of the rock is subjected to tensile shear stress.When the initial fracture length a0 is less than 2m,the dangerous rock is mainly damaged by type I tension.When a0 is greater than 2m,the damage of dangerous rock is the joint action of type I tension and type II shear.(4)Based on the principle of conservation of energy,the energy equations of the masonry-type dangerous rock mass system are established,and the energy criterion equation for the disintegration damage of the dangerous rock mass is established.The results show that when d V(29)0,the dangerous rock masses would not be disintegrated;when d V(28)0,the critical state of the disintegration phenomenon of the masonry type rock was judged;when d V(27)0,the collapse of the masonry-type dangerous rock occurred.Taking Wangxia W2-2 dangerous rock as an example,it is predicted that dislocation will occur when the dangerous rock mass deflects to a tilt angle of 31°.(5)The composition of the minerals that make up the base of the weak base rock of Wangxia Caves is used as the entry point,and the soft rock material(cement: sand:water: clay: kaolin = 1:3.3:0.7:0.58:0.29)is prepared in different pH environments.Under the combination of pH value(4,5.5,and 7)and different soaking time,the change law of the shear strength parameter value c and ? is explored through the triaxial test.In the acidic environment,the cohesion force and internal friction angle will decrease as the soaking time increases.Under the same number of days of soaking,the cohesion and internal friction angle will be lower with pH value,and the decrease will be more obvious.The change of cohesion force and internal friction angle will be greatest at the initial soaking days,and then the decreasing rate will gradually ease.The reduction rate of cohesion is lower than that of the internal friction angle,which indicates that the internal friction angle of soft rock is more sensitive to the change of pH.(6)Through FLAC 3D numerical simulation software,simulation of Wangxia W2-2 dangerous rock under the influence of horizontal seismic force,shear strength parameters of rock mass progressively,simulates the process of deformation and failure of the dangerous rock mass,and analyzes it in different works.The displacement cloud diagram,stress field,maximum shear strain increment,andstability factor at different time steps indicate that the most important reason for the increased deformation and damage of dangerous rock is due to the weakening of the shear strength parameter of the rock mass.The horizontal seismic force will exacerbate the process of rock-plastic flow-cracking and collapse.