Research On The Stability And Support Optimization Of Highway Tunnel Entrance Slope

In the past few years,the construction of mountain tunnel has greatly optimized traffic lines and improved the people's travelling efficiency,however,it is also accompanied by great hidden danger.The safety of slope at the entrance of tunnel directly affects the construction safety and the future use of the tunnel.The stability of tunnel slope is the critical to ensure the safety of tunnel.Therefore,the slope stability and support of tunnel entrance are the very important to ensure the safety of tunnel construction.In this paper,Taking the tunnel entrance 1 of manyanpo as an example,the stability of the slope at the tunnel entrance is analysed using FLAC 3D software section,the stress law of the anchor cable frame beam under different working conditions is analyzed by numerical simulation method.Based on the theoretical calculation method,combined with the numerical simulation calculation,the optimal support scheme is proposed.This study can provide technical reference for the optimization design of the anchor cable frame beam in such tunnel engineering.The main work and research results are as follows:(1)This paper reviews the relevant literature of tunnel engineering and tunnel slope,explains the importance of the slope at the tunnel portal in the whole tunnel construction and operation period,analyzes the factors affecting the stability of tunnel portal,and summarizes the failure mode and supporting measures of the tunnel entrance slope.(2)Taking the slope of tunnel entrance 1 of Manyanpo as an example,the general law of tunnel excavation on the stability of the slope above the tunnel mouth is studied by FLAC 3D software.The main reason for the instability of the slope above the tunnel mouth is shear failure.After that the slope is unstable,the sliding surface formed by the shear stress will slide out in the form of rigid body.In view of the instability of such slope,the most useful supporting measures are slope cutting and prestressed anchor cable frame beam support.(3)Based on the actual engineering situation of Manyanpo tunnel 1,numerical calculation and analysis are carried out under three conditions: natural state,slope reinforcement state and slope reinforcement and excavation state.The results show that the slope can ensure the normal operation and stability of the tunnel after supporting.When the slope is excavated in different stages,the closer the slope bottom,the greater the displacement increment and the greater the bending moment increment of frame beam,the more the actual situation is in the inter reinforcement project,the slope stability can be further strengthened by adding prestress to the slope above the tunnel mouth or increasing the cross section of the frame beam.(4)Combined with the actual reinforcement of the slope of the Manyanpo tunnel 1,the supporting structure parameters(anchor rope spacing,anchor rope inclination,anchoring force)of the pre-stressed anchor rope are optimized,then combined with Orthogonal experimental design,and finally the optimal structure parameters are obtained when the anchor rope spacing is 4 m,the anchoring angle is 20 degrees,and the pre-stress is 600 k N.Through comparative analysis,it is suggested that the optimized structural parameters can play a better role in support,and the research results provide some references for the excavation of such mountain tunnels(the slope with grade V surrounding rock and groundwater development).(5)The influence of different structure parameters on the prestressed anchor cable frame beam system is studied and analyzed.The following conclusions are drawn: in the support design,the slope compression can be increased by reducing the anchorage angle,the spacing between the anchor cables and the anchoring force;the stability of the mountain slope can be improved by increasing the cross section between the frame beam and the frame beam near the tunnel mouth;In the prestressed anchor cable frame system,the lateral moment is about 1-5 times of the main moment,so the influence of lateral force can not be ignored.