| With the sustained and rapid development of economy since the reform and opening of China, the development of energy, resources, transportation, city construction and engineering has been greatly stimulated. At present, a large number of domestic engineering project has also brought corresponding security problems.Especially, in our country there are numerous,large and medium sized open pit mines, which the final design height of slope is usually 300m-500m, and the trend is higher and steeper.Its stability and reliability will directly affect the construction quality and safety. IF accidents occur,it often bring huge property losses and a large number of casualties. Therefore, study on the stability of slope is of great significance to the mine.Mine slope instability, often in a certain geological conditions, due to the influence of excavation,rainfall and other factors, which breaks the original balance condition. Instable rock mass fall under the action of gravity along a surface and the landslide come into being. If the mine stability research is insufficient, it is easy to cause the unreasonable exploitation of mines, which led to the occurrence of geological disasters. This thesis combine the project-"Sichuan Jinding (Group) Limited Company Mount Huangshan limestone mine 8000000 tons/year technical renovation project demonstration and optimization research of end slope stability ".Mount Huangshan limestone mine existing production capacity is 2600000 tons/year, which will be totechnological transformated to 8000000 tons/year, according to the new design of excavation scheme.Using the discrete element strength reduction method, analyze the stability of the mine, the deformation and failure mechanism of the slope, in order to ensure safety in production of the mine. The mining area terrain overall tendency is ne-trending, the terrain of North East and South East part is steep, the south is relatively gentle, valley and stream can be seen here,in the east is Gan Xi ditch, in the west is Huang Dong Er ditch, in the central is Luo creek ditch,which divide the Mount Huangshan mining area into east, west two parts.This terrain is favorable to natural mine drainage, the lowest elevation of the mine is 507m,for the lowest water erosion base level, ignoring seepage fieldto the stability analysis. The laboratory direct shear test and triaxial test are simulated by PFC to research on rock failure and deformation mechanism.Combined with the strength reduction method,the PFC model of mine slope is established, and the excavation unloading effect of slope is analysed, obtaining the following research results:(1)Through the analysis of Mount Huangshan mining existing data and investigation results, obtain the geological structure, mine engineering geological and hydrology geological conditions, mine design parameters.IN Mount Huangshan limestone group, thick and middle thick layer of limestone exsit interlayers of thin to thick laminated shale, bedding sandy and silty sand clastic limestone. Beddings are developed commonly, the interlayer bonding is soft.rock and the interlayers rock can be softened by water easily.Because of strata inclination and slope direction are unanimous, the slope structure of mining area is unstable, the mud layer consist of the potential sliding surface of the mining area and landslide slip surface. There are two developed sets of joints in the mining area, but because of the different lithology, its degree of development is not the same.IN upper Qixia group, joints are deleloped, its density is 0.96～2.53/m;the lower part of Maokou group, joint density ranged from 0.08 to 2.08/m; the lower Qixia group joint is not very developed. In addition, the shallow depth, poor extension joints created by the rock blasting, which make the integrity of rock mass destructied, strength reducted, may cause local instability of rock mass.(2) For further understanding of the failure analysis of characteristic and mechanism of rock and structural plane, using particle flow software PFC2d and simulating laboratory direct shear test and triaxial test.From the microscopic view of the weak interlayer and limestone test,get more profound understanding of the deformation and destruction. The study found that, in the shear process of weak interlayer, the particles after part of surface support more shear stress.When stress displacement curve exhibited shear plastic characteristics in shear process, tension crack emerged,and the whole number of crack increased dramatically. With the crack development of the structural surface,the normal contact number will continue to decrease, and caused the increasing of contact pressure between particles, resulting in that the shear crack and tensile cracks along the structural surface increased, and the formation of broken shear band. In the limestone three axial compression test simulation, limestone crack damage rules was obtained: during growth of the axial strain and stress, when crack initiation point is reached,crack startin the upper right corner of the rock. With the load continuing, ultimately a through crack surface formed, and the rock damage along the surface; According to the monitoring and analysis of energy,obtaing the energy change law of the limestone:under the confining pressure and axial compression, boundary energy make rock energy accumulated, particles first overcome bond and cracks continue to expand, form a through crack, then the friction energy of rock play the main effect,the rock slide along the crack surface at last.(3) Establish the PFC slope model mine and analyse the excavation of slope. In the first step of the excavation, deformation and failure is not obvious, slope is basically stable and safe. In the second step of the slope excavation process, slope produce deformation and failure in local, but the slope basically is in a safe state. Slope in the third step of excavation process is still in steady state, but compared with the second excavation of the results,can be seen in the slope new cracks appear. Slope produces a lot of cracks in the excavation of the fourth step of the process, and have a trend of through the slope, further impact outside like blasting,rainfall and other factors, will lead overall failure.(4) According to the analysis of excavation, excavation unloading effect is more obvious for the region of Liangshan group, while the sandstone not.By using the method of partial reduction, based on the strength reduction of discrete element formula, rock strength parameters of Liangshan group formation is reduced ot the analysis of the damage development. With the reduction of slope parameters, contact bond failure area continues to expand. When the strength reduction coefficient is 1.25, the slope is in extreme danger sliding failure may occur at any time.At last, the stability coefficient is get to be 1.25, which cant not satisfy the safety of the mine. |
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