| With the development of China’s economy,the construction of infrastructure facilities such as roads and railways is increasing day by day,and tunnels have become the best way to solve the problem of mountain blocking.Among them,the small clear distance tunnel has become the first choice of tunnel planning and design under special conditions because it occupies less land and is beneficial to the overall highway alignment planning and alignment optimization.However,different from the general separated tunnels,because of the close spacing between tunnels,the plastic zone may overlap,so the middle rock is the most dangerous position in the construction process,so the stability of the middle rock becomes the key factor for the safe construction of the small clear distance tunnels.Knowing the stress state and change law of the middle rock can provide great help for the stability of the middle rock in the construction process of the small clear distance tunnel,and choosing a reasonable reinforcement method of the middle rock can ensure the safety and stability of the construction.Micro-seismic monitoring technology,as a new technology that can monitor the development of micro-cracks in rock mass,can obtain the time,location and strength of cracks before dangerous conditions occur,and provide valuable data for the study of mechanical state of tunnel surrounding rock.As a cutting-edge modeling software,PFC discrete element particle flow software can build a jointed rock mass model that is in line with the actual construction situation on site.Compared with the traditional finite element software,PFC discrete element particle flow software can closely reflect the crack development,stress transmission path and displacement in surrounding rock,and help researchers analyze the micro-changes in surrounding rock during tunnel construction,and then infer the possible danger and risk factors.Based on the No.1 tunnel in Qichong Village,Guiyang City,this paper combines the"space-time intensity"information of micro-seismic monitoring data with PFC2D modeling,and does the following work:（1）Analyze the on-site micro-seismic monitoring data,and obtain the time,space and intensity data of the development of cracks in the surrounding rock during the whole process of the brewing,development and occurrence of the danger in the two tunnel sections according to the"time-space intensity"characteristics of micro-seismic events.Combined with the analysis of the geological survey report of the tunnel site area,the damage law of the middle rock caused by the excavation of the small clear distance tunnel is obtained.（2）Use PFC2Ddiscrete element particle flow software to calibrate the mesoscopic parameters of the rock mass in the tunnel site area,establish a jointed rock mass model according to the geological survey report,and determine the minimum REV size of the rock mass in the tunnel site area.A tunnel construction model is established to analyze the characteristics of crack development,disturbance zone distribution,force chain distribution,stress changes at key positions,and middle rock deformation during the tunnel construction process.Combined with on-site micro-seismic data,the cause of the tunnel danger and the middle rock before the occurrence are obtained.Stress and failure characteristics.（3）Relying on the working conditions and geological conditions of the on-site tunnel,a model is established by changing the number of joints,inclination and density,and the thickness of the rock column in the middle.The characteristics of rock deformation and other characteristics are analyzed,and the influence characteristics of joint occurrence,density,and thickness of inter-rock pillar on the stability of inter-rock in small clear distance tunnels are obtained.（4）Based on the above analysis,the reinforcement mechanism of rock inclusion in small clear distance tunnel is studied.Aiming at the numerical modeling of small clear distance tunnel,the grouting optimization is studied.For grouting in the non-area inside the middle rock,the contribution of various conditions to the stability of the middle rock is calculated and analyzed,and the effective measures for grouting reinforcement of the middle rock in the small clear distance tunnel are obtained. |
