Study On The Model Construction And Mechanical Response Characteristics Of Karst Fissured Rock Mass

With the continuous extension of human activities to the nature,frequent engineering construction such as mining activities are changing the occurrence environment of rock mass on a large scale,resulting in increasingly complex mechanical behavior of rock mass.Karst fissured rock mass is the product of long-term geological environment in karst area.Its mechanical response characteristics are affected by fracture surface and dissolution.At present,there are few reports on the mechanical response characteristics of karst fractured rock mass.In this paper,the karst fissured rock mass is taken as the research object,and the model of karst fissured rock mass is constructed by means of field measurement,probability statistics,indoor test and numerical simulation.Based on this,the mechanical response analysis of karst fissured rock mass is carried out,and the influence mechanism of dissolution and fissured surface on the mechanical response of rock mass is discussed.At the same time,the collapse in Zhangjiawan,Guizhou Province,is taken as an example to analyze its mining process The mechanical response characteristics of deformation and failure evolution in dynamic process.The main research contents and conclusions are as follows:(1)The spatial shape of the fracture surface is almost rectangular,and the development of joints between the layers is almost vertical.Although joints are not strictly parallel,most of them rarely cross,and the rock mass is cut into blocks of different sizes by the fractures.The two groups of joint tendencies in the study area are all normal distribution,and the trace length is negative exponential distribution.The dip angle of j 1 is uniform distribution,and the spacing is lognormal distribution.J 2.The dip angle obeys Weibull distribution,the spacing obeys negative exponential distribution;the bedding spacing obeys Weibull distribution;the Rev size of fracture rock mass is determined to be 1 m × 1 m × 2 m.The macroscopic mechanical parameters obtained by uniaxial compression numerical simulation test and direct shear numerical simulation test of fracture surface are consistent with the macroscopic mechanical parameters obtained by the laboratory,and meet the compression tensile strength ratio of rock mass,which shows that the microscopic strength parameters obtained by calibration are reasonable;the karst fracture based on random pore corrosion model and fracture corrosion model can reasonably describe the rock mass Dissolution.(2)The existence of fracture surface weakens the uniaxial compressive strength and elastic modulus of rock mass,increases the degree of uniaxial compression deformation of rock mass,and promotes the mechanical properties of rock mass to show anisotropic characteristics;the influence of pore type dissolution on fracture rock mass is more significant than that of fracture surface dissolution;although the dissolution of fracture surface breaks the bond strength of fracture surface,the effective contact area of fracture surface does not decrease,In addition,it also retains complete friction characteristics,so the impact of fracture corrosion on the macro mechanical properties of fractured rock mass is not obvious as a whole.(3)Under the condition of triaxial compression,the effect of confining pressure strengthens the strength parameters of karst fractured rock mass and weakens the anisotropic characteristics of the mechanics of karst fractured rock mass,which shows that karst fractured rock mass has obvious confining pressure effect;pore corrosion has greater influence on the model than fracture corrosion under triaxial compression;fracture,confining pressure and dissolution jointly control triaxial compression Under the condition of dissolution,the formation of fissures and the increase of confining pressure change the tensile failure of rock mass to the shear failure of fracture surface,which shows the phenomenon of changing from one to the other.Under the action of fissure dissolution,the development of fissures does not fluctuate much except that they also have confining pressure effect.For pore dissolution,the total amount of fissures decreases with the increase of dissolution,so in the case of porosity dissolution Erosion has the greatest influence on the dissolution of fractured rock mass.(4)The existence of fractures makes the rock mass have a high sensitivity to the process of unloading confining pressure.In the process of unloading confining pressure,the fracture surface always breaks first,and then in the process of shear slip deformation of the fracture surface,it gradually causes the failure of the rock mass originated from the fracture surface.The existence of the fracture surface has a certain control effect on the failure of the rock mass during unloading confining pressure.After the removal of the confining pressure,the rock mass with karst fractures can play a role However,a large number of damage fissures are developed under the relatively complete external structure,which is the main reason for the increase of the sensitivity of the released confining pressure rock mass,and it is easy to cause the overall failure under the external interference;although the dissolution of fissures does not have a great impact on the overall strength of the model,under the condition of complete unloading,the dissolution of fissure surface often increases the risk of rock mass falling and collapse,and the rock dissolution The failure mode of fractured rock mass will change with each other under different environmental conditions,which is caused by the different sensitivity of various factors inside the rock mass to the environment.(5)After the coal seam is mined,the unloading effect of the goaf will transfer the deformation to the top of the slope,resulting in the stress concentration at the top of the slope,which is shown as the tensile shear stress,while the tensile strength of the fissured rock mass is almost 0,so the deformation of the top of the slope is severe;with each mining,the failure of the collapse physical chain is gradually intensified,and the failure location is mainly concentrated in the middle and lower part of the collapse body The rock mass structure corresponding to the soft and hard interbedding of the collapse body is a destructible area;after the mining of coal seam,it provides accelerated conditions for the further development of the collapse body,and the fracture expansion provides convenience for the occurrence of dissolution,in which the dissolution includes both pore dissolution and fracture surface dissolution.In a long period of time,the deformation and dissolution of the slope body are carried out at the same time,affecting each other,resulting in eventually The collapse occurs;the total movement time after the collapse is about 32 S,of which the main sliding time is about 26 S,and the energy in the process of the collapse mass movement is huge,causing huge loss of life and property.When most particles are relatively static,only some particles with large kinetic energy continue to move and accumulate,and the longest distance of the collapse mass movement is more than 600 m,which is consistent with the actual movement distance of the collapse mass.