Study On The Influence Of Rock Mass Joints On The Surrounding Rock Stability Of Undercut Metro Station Tunnels

In recent years,major cities have been vigorously building subway projects to ease the pressure of travel in daily life.For the development of underground space,it is inevitable to encounter complex geological conditions,especially rock masses with structural planes.Through extensive research and experiments,the mechanical strength of the structural plane is much lower than that of the intact rock.Due to the existence of the structural plane,the integrity and stability of the rock mass are weakened,and the mechanical properties and stability of the jointed rock mass are stabilized.Sexuality plays a controlling role.Therefore,the analysis of the influence of the distribution and mechanical properties of the joint surface on the tunnel excavation in the jointed rock mass is very important.Based on the Tushan station of Chongqing Rail Transit circle line,this paper uses PFC^2D particle flow software to analyze the influence of joints on rock mass properties and tunnel surrounding rock stability.The main research contents are as follows:Firstly,by changing the joint dip angle and joint position,the influence of the change of joint dip angle and position on the macroscopic mechanical properties,failure morphology and crack development process of jointed rock mass is studied.The simulation results show that with the same joint position,the peak strength of the jointed rock mass decreases first and then increases with the increase of the joint inclination angle.When the joint inclination angle is 60°,the peak strength of the rock mass is the smallest.And the failure mode is mainly shear failure;except for the joint inclination angle of 60°,the peak intensity of the joint at 1/2>the peak intensity of the joint at 1/3>the peak intensity of the joint at 1/4.Secondly,the excavation of the surrounding rock containing joints is simulated.By changing the inclination and position of the joints,the influence of different angles and positions of the joints on the failure modes and fracture distribution of the surrounding rock mass after tunnel excavation is studied..The simulation results show that as the joint inclination angle increases from 0 degrees to 90 degrees,the damage of the tunnel dome and the side wall becomes more and more serious;when the joint plane is located below the tunnel excavation surface,after the tunnel excavation,the hole The surrounding rock mass damage is the most serious;when the joint surface passes through the tunnel excavation surface,the rock mass near the joint surface is more deformed;when the joint surface is above the tunnel excavation surface,after the tunnel excavation,the tunnel dome and The damage at the arch is the most serious.Finally,through the excavation simulation of the Tushan station of Chongqing Rail Transit Line,the damage of the joints after the excavation of the Tushan station tunnel is studied to provide some guidance and suggestions for the actual construction process.The simulation results show that the cracks generated by the middle rock between the two holes first appear at the joint surface,and then continue to expand near the joint surface,causing a large number of cracks in the middle rock,and the place with the most damage.