Study On The Stability Of Slope At The Portal Of Seperated Neighborhood Tunnels And Numerical Simulation Of Tunnel Construction Method

In recent years, as the development of economic, the investment of infrastructure construction is increased in our country, in mountain areas, the construction of highway is limited to engineering geology, hydrogeology conditions, human factors and the trend of the road, neighborhood tunnels are widely used with its unique advantages. Lots of tunnels were inevitably built at the bad geological areas, it is very easy to lead to landslides, collapses, ground cracking etc. through tunnel excavation, so it’s extremely important to study the stability of slopes at the portal of tunnels. In this paper, on the background of Changwang2#tunnel of Yanling-rucheng highway in Hunan province, combining field monitoring and numerical simulation, comprehensively evaluated the influences to the stability of tunnel entrance while tunnel excavation. Main works as follows:(1) Introduced the project summery of Rucheng end of Changwang2#tunnel, according to the actual fact, designed the monitoring schemes, through the analysis of the data of site monitoring, obtained the slope deformation rule and the tunnel deformation characteristic while tunnel excavation:the biggist deformation of the slope happened in the area surrounding the tunnel axis, and the settlement became smaller when far from it, the biggist deformation of the tunnel toke place in the vault area, with the increasing of the depth, vault deformation gradually decrease;(2) According to the deformation rule of surrounding rock, obtained the maximum deformation occurred nearby tunnel vault, put forward a new method to determine the length of tunnel entrance, the conclusion is further improved the method of the Code for Design of Road Tunnel;(3) Put forward a new method to find the sliding surface by using GPR, and applied it in the slope of Changwang2#tunnel, the results shows that the sliding surface found by GPR almost the same with the theoretical calculation consequence, proved the GPR technique has a good application prospect in slope engineering geologic surveys;(4) Based on the numerical analysis, established the model of the natural slope and the brushed slope, analysis their stability, and get the safety coefficient and the most dangerous sliding surface by using strength reduction method;(5) Established the3-dimension numerical model of neighborhood tunnel, analysed the influence of divisional excavation, the calculation result shows that the shallow section has a bigger surface subsidence compared to the deep area, and the settlement of vault is more and more big while the depth is increasing. Pipe roof, system bolt, primary support structure and linings can undertake and transmit the load of surrounding rocks, and they are very important to the safety of tunnel. Compared with field measured result, the calculating model can be well reflected in engineering practice, and can also provide references for similar project.