The Research Of Parameters Optimization Of Talus Tunnel’s Construction In Yunnan Mountainous Areas

The talus are widely distributed that bring a lot of difficulties to the tunnel construction in Yunnan. This unstable engineering geology is easy to cause the collapse, lining cracking, surface deformation and landslide in the construction of tunnels which brings a lot of losses. In recent years, more and more expressways are building in the western mountainous areas that makes solving many geological problems related to the talus is becoming more and more urgent. To better understand the characteristics of the talus and in order to guarantee the talus tunnel construction’s safety and fast, this paper combined with practical engineering, through researching and summarizes the characteristics of the talus and uses theoretical analysis and the theory of beam on elastic foundation and the method of numerical calculation, analyses and researches the excavation footage, the step length of three and seven steps method and the length and the angle of locking anchor pipes. The optimum construction parameters is given for the shallow buried section of tunnel entrance. The main research contents and results are as follows:(1) On the basis of research, analyzing characteristics, form conditions and engineering characteristics of the talus and summarizing the construction parameters and measures of the typical talus tunnel.(2) According to the Terzaghi consolidation theory and silo theory, putting forward a calculation model of excavation footage of talus tunnel’s shallow buried section. The results show that the reasonable excavation footage is 1.0m under the support of pipe roof.(3)Through the use finite element software Midas NX, completing the 3D simulation analysis of seven step three step process about talus tunnel’s shallow buried section and systematically analyses the stress and deformation of surrounding rock and supporting structure under different construction parameters. results are as follows:1) With the increase of step length, vertical displacement and Horizontal convergence value of surrounding rock are bigger, then axial force and bending moment of the steel arch are gradually reduced, shotcrete layer’s tensile stress is also reduced. From the point of deformation of surrounding rock and support structure, From deformation of the surrounding rock and the force of the support structure, the step length of the shallow cave tunnel is recommended to take about 4m.2) With the locking anchor pipes’insertion angle increases, the horizontal displacement of the stage is gradually reduced, the horizontal displacement of the middle and lower steps is decreased firstly, then the trend is increasing. It is suggested that the insertion angle of locking anchor pipes should be 20°～30°.3) With the length of locking anchor pipes increases, the horizontal displacement of arch and side walls and the corners decreases, when the length of locking anchor pipes exceeds 4.5m, the horizontal displacement becomes flat. The length of locking anchor pipes is recommended to take between 4.5m-6m.