Study On The Formation Mechanism Of Gently Inclined Carbonate Rock Collapse Under Differential Dissolution

The special stratum lithology,hydrogeology and climatic conditions in Guizhou area make most of the collapse disasters in this area have a close relationship with dissolution.This paper takes the Huishui Xinzhai collapse as an example to study the chemical composition and microstructure of the limestone in the study area,analyze the dissolution rate of the limestone under different stress states,and obtain the factors that affect the differential dissolution of the limestone.Differential dissolution promotes the formation of cavities in the thin rock mass at the bottom of the slope,and the influence of cavities on the deformation and failure of collapsed bodies is simulated by UDEC.The main content and research results are as follows:(1)The Huishui Xinzhai collapse is a typical near-horizontal carbonate collapse.The upper part of the dangerous rock mass is thick limestone and the bottom is thin limestone.The dissolution in the study area is strong,and a large number of dissolution phenomena can be seen everywhere.There are several horizontal and vertical dissolution fissures on the sidewall and rear edge of the collapsed body.There are cavities in the thin limestone at the bottom of the collapsed bodies,and there are also a large number of dissolution marks in the cavities,and the rock mass is relatively broken.(2)Unfavorable combination of lithology and humid and rainy climate are the basic conditions for the deformation and failure of collapsed bodies.Strong dissolution and the development of cavities are the main controlling factors for the instability of collapsed bodies.The deformation and failure of the collapsed body is mainly divided into the following stages: the formation of a concave rock cavity in the thin layer at the bottom of the collapsed body;the tendency of the dangerous rock mass to dump toward the empty surface,and the trailing edge fissures gradually form;the center of gravity of the layered rock tilts forward,the slope is tilted toward the open surface,and the trailing edge fissures are gradually penetrated;the dangerous rock mass loses stability and collapses due to a tipping-cracking type.(3)The research on the influence of the chemical composition and microstructure of the rock on the differential dissolution has found that:(1)The thick layer of limestone is dolomitic limestone;the thin layer is pure limestone.(2)The thick layered limestone is silt crystalline limestone,and the crystal structure on the surface of the rock mass is well developed;the thin layered limestone is micrite limestone,and the crystalline grains of the rock mass are small and poorly developed.The thin layer of limestone is more conducive to the occurrence of dissolution in terms of chemical composition and microstructure.(4)Through the stress corrosion test,it can be found that the compressive strength of the rock sample is reduced under the action of stress corrosion.When the other dissolution conditions are the same except for the stress,the degree of dissolution development of the rock sample increases as the stress increases.The specific performance is: the dissolution form of the sample surface gradually increases with the increase of stress,the dissolution quality of the sample increases with the increase of stress,and the dissolution rate of soluble rock increases with the increase of stress on the sample.(5)UDEC numerically simulates the influence of concave rock cavity development on slope stability,and the following conclusions are obtained:(1)In the initial state of the slope,the karstification of the slope has not yet developed,and the overall stability of the slope is good.(2)The development of the cavities plays a vital role in the deformation and destruction of the collapsed bodies.The center of gravity of the upper thick rock mass gradually shifts to the empty space with the development of the cavities,and the dangerous rock mass tilts towards the empty surface.The tensile strength of the rock at the trailing edge is insufficient,so that the trailing edge crack is penetrated under the action of tensile stress,and the collapsed body is deformed and damaged.