| There are a large number of fissures in the rock mass with different shapes.Some are only a few centimeters long,while others run through the whole rock mass;The crisscross cracks cut each other with the excavation face of the roadway,forming movable blocks on the excavation face.If the block is unstable,it will produce new free face,which may form new movable blocks,and then affect the safety of the whole rock mass.At the same time,the crisscross fracture is a good flow channel for groundwater.After the excavation of roadway,the excavation face will become a new drainage surface,and the flow state of groundwater will change significantly.The existence of groundwater will reduce the effective force on the block surface,and the infiltration of water on the structural plane will reduce the friction coefficient of the block surface,thus affecting the stability of the block.Therefore,the influence of water pressure on block stability should be considered.Based on the block theory,this paper searches the movable block on the excavation face of the roadway in the study area,and calculates the water pressure on the excavation face.Through the finite element software simulation,the influence of water pressure on the stability of the block is obtained(1)Moving block search for excavation boundary.Based on the site conditions of nuclear waste disposal laboratory,the random discrete fracture network is established,the plane equation of fracture disk is solved,the double roadway model is established,the intersection line between the spatial disk and the excavation face is solved,the closed circuit on the excavation face is searched,and then the intersection line of the spatial disk is solved,the closed line of the body is searched from the closed circuit,and the movable block on the excavation face is obtained.The simulation results show that the blocks are mainly concentrated in the two main roadway faces of the double roadway,the volume and mass of the blocks are discrete,and the location distribution is random.(2)The geometric connectivity path between the boundary block surface and the computational boundary is searched..Based on the breadth first search algorithm,starting from the corresponding fracture surface of the block,all the fractures connected with the block surface and the calculation boundary are traversed,and then the dead water end is deleted to obtain the three-dimensional seepage network containing the block surface.The search results show that the number of fractures connected with the block fracture surface accounts for more than 70%of the total number of fractures in the region,and the fracture connectivity in the region is good.(3)Calculation of water pressure on block surface.According to the graph theory pipe network method,the equivalent pipe network model is established for the study area,the node head value in the study area is calculated,a distribution form of water pressure on the block surface is proposed,and the water pressure on the block surface is calculated.The calculation results show that the water pressure on the block face at the top of the roadway is small,and that on the block face near the bottom of the roadway is large.The maximum water pressure is 10~6Pa.(4)The influence of water pressure on block stability is analyzed.The finite element software is used to simulate the situation with and without water pressure.The simulation results show that the water pressure has little effect on the stable block.For the unstable block,the water pressure can change the block from limited sliding along the structural plane to falling away from the rock mass,accelerate the instability speed of the block,change the instability mode of the block,and change the change trend of the block displacement at any time.The simulation results show that the water pressure has a significant effect on the block stability. |
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