Study On Perilous Toppling Rock In Limestone Area

According to the statistics of the Geological Disaster Center of the Ministry of Land and Resources,the collapse disaster is one of the major geological disasters in China,accounting for 20% of the national geological disasters.The dangerous rock collapse is a common geological disaster of the high slope rock mass.The rock mass in the limestone area has many internal structural planes,and different structural planes combine to form a masonry structure.At the same time,the lithology characteristics of the lower base affect the stability of the rock mass.In this paper,the dangerous rock belt of the Yanziyan Formation in Nanchuan,Chongqing is taken as the research area.The geological survey of the area shows that the proportion of dumping damage in the rock mass reaches 66.67%.In this paper,the limit equilibrium method,fracture mechanics,reliability theory and numerical simulation are combined to study the dumping.The rock mass destruction phenomenon and stability analysis,the research results obtained are as follows:(1)Through the geological survey and engineering geological conditions of the Dianziyan dangerous rock belt,the dangerous rock mass masonry structure is the result of multi-factor coupling.The lithologic combination of soft and hard rock facies,the unloading of cliffs,the formation and combination of structural planes,and the formation of rock cavities constitute the internal conditions for the formation of dangerous rock masses;rainfall and dissolution,and the formation of goaf in mining to accelerate the formation of dangerous rocks condition.The combination of soft and hard rock lithology forms three typical structural planes,namely horizontal layered primary structural plane,steeply dumped fractured structural plane and soft-hard rock interface tensile cracked structural surface,and dangerous rock mass presents with masonry structural surface features.(2)Through the analysis of the mechanical model of the dumping dangerous rock,the fracture mechanics model is established,the fracture failure conditions of the rock mass are analyzed,and the basis of the composite crack propagation under the support of the weak rock mass is derived,which is based on the stress intensity factor.Dangerous rock mass stability coefficient expression.The crack propagation,stress intensity factor and stability coefficient are analyzed by examples.(3)Considering the direction of seismic force,construct the stability stress model of the dumping dangerous rock mass,and derive the expression of the most dangerousaction direction of the earthquake.Taking the dumping type dangerous rock mass of Jinfoshan in Nanchuan of Chongqing as an example,the angle between the most dangerous seismic action direction of the dangerous rock mass and the horizontal plane under the combination of two working conditions is calculated.Under the working condition,the deflection angle of the most dangerous seismic action is 5°.The range,the deflection angle of the most dangerous earthquake action direction under working condition is about 10°.When the reliability of the stability of the dangerous rock is analyzed by the reliability analysis,the most dangerous seismic action direction and the horizontal deflection angle are small.When the length of the main control structure increases,the most dangerous seismic action direction and The horizontal deflection angle is significantly increased.As the depth of the rock cavity increases,the most dangerous seismic action direction and horizontal deflection angle increase under the two conditions,but the increase angle is smaller;with the increase of the main control structure plane inclination angle,the most dangerous seismic action direction and horizontal direction The deflection angle is gradually reduced,but the reduction is small.(4)Using FLAC 3D numerical simulation,under the five conditions of natural,heavy rain,seismic force and strength parameter attenuation,the dangerous rock mass is found to be stress concentrated at the tip of the main control structure and the top of the pedestal rock mass.In the area,the shear strain increment and plastic yield zone of the dangerous rock mass are mainly concentrated in the porphyrite rock mass,and the pedestal rock mass is the determinant of controlling the instability and failure of the dangerous rock mass.The external force is the induced factor of the dangerous rock mass,and the stability is passed.The calculations show that the dangerous rock mass is unstable in the five working conditions.Working condition 1.Working condition 2 is prone to seat failure and instability under the action of water pressure.The working conditions of the third,fourth and fifth working conditions are prone to external deformation.The damaged rock mass can be tilted to the outside under the action of seismic force.pour.Through numerical simulation,the stability coefficients of the five working conditions are gradually reduced and unstable: the stability coefficient of the working condition is 1.02,the stability coefficient of the working condition is 0.87,and the stability coefficient of the working condition is 0.85,and the dumping failure of the dangerous rock mass is finally caused;The stability factor of the working condition is0.74,and the stability coefficient of the working condition is 0.66.