Stability Analysis And Deformation Control Research Of Surrounding Rock In Shallow Buried Small Clearance Tunnel Entrance Section

With the high-quality development of my country’s economy,the construction of expressways in my country’s transportation sector has developed rapidly.There are many hills and high mountains in the western region.In order to further shorten the expressway distance,a large number of tunnel projects are included in the construction of western expressways.Compared with conventional separated tunnels,small-space tunnels occupy a smaller area,have a smoother plane and linearity,meet the bridge-tunnel connection conditions,and meet the aesthetic requirements of construction engineering and nature.Therefore,small-space tunnels are common designs for highway construction in mountainous areas.plan.However,the stress state of the surrounding rock of the small clear distance tunnel is complex.The tunnel entrance is the key project of the tunnel engineering,and the buried depth of the tunnel entrance section is shallow.The soil has been subjected to natural weathering for a long time,and the strength of the surrounding rock is low,and the self-stabilization ability is poor.In the case of unfavorable surrounding rock,tunnel engineering safety accidents often occur at the tunnel entrance,so reasonable construction methods and support measures must be adopted to control the deformation of the surrounding rock and ensure the stability of the surrounding rock.Based on the background of a shallow-buried small-space tunnel project in Chongqing,this thesis adopts research methods such as theoretical analysis,numerical simulation and on-site monitoring to analyze the stability of the surrounding rock of the tunnel entrance section project under the design conditions.According to the characteristics of the supporting project,carried out the stability analysis and deformation control research of surrounding rock,and obtained the following main research results:(1)Excavate the tunnel according to the designed construction method,and use numerical simulation methods to analyze the surrounding rock stress field,displacement field,plastic zone distribution,surface settlement,and the force state of the advanced support and initial support.The stability of the surrounding rock of the shallow-buried small-space tunnel is analyzed,and the deformation and stress of the surrounding rock and the change law of the force of the supporting structure are obtained.(2)Using the numerical simulation method,analyze the deformation control effect of the surrounding rock under different construction methods in the entrance section of the shallow-buried small-clear distance tunnel,and study the displacement field,stress field,plastic zone and support of the surrounding rock under different construction methods.According to the force condition of the protective structure,the reasonable construction method of the project is the step method.(3)Based on a reasonable construction method,under the condition of different longitudinal distances between the face of the shallow-buried tunnel with a small clear distance(left and right line tunnel excavation,the face of the face is staggered)Numerical simulation analysis was carried out on the control effect of spacing on surrounding rock deformation,and it was concluded that the reasonable longitudinal spacing of the tunnel face based on the project is 1.5B(B is the excavation width of the tunnel).(4)Aiming at the different support parameters of the advanced pipe shed and the advanced small conduit,through the numerical simulation analysis of the deformation of the surrounding rock and the force of the support structure,a reasonable advanced Support parameters.The reasonable parameters of the advanced pipe shed are: the pipe diameter is 108 mm,the circumferential distance is 35 cm,and the pipe length is 20m;the reasonable parameters of the advanced small pipe are: the pipe diameter is 45 mm,the pipe length is 4m,and the external insertion angle is 15°.(5)During the tunnel construction process,the monitoring measurement control technology was adopted to analyze the dynamic deformation of the surrounding rock at the tunnel entrance section,and the numerical simulation calculation results were compared with the measured data to verify the effectiveness of the surrounding rock deformation control measures.