Study On Optimization Of Initial Support For Soft Rock Tunnel

Based on the Pingdingshan Tunnel in Yantai,his paper studies the theory of soft rock highway tunnel,designs different working conditions of steel arch,spray concrete and anchor in initial support combined with tunnel design scheme and code for Design of Highway Tunnel.Finally,numerical simulation of each working condition is carried out by finite element software,and the optimal spacing of steel arch,the type of steel arch,shotcrete thickness,anchor length and anchor spacing are selected according to the calculation results.(1)The interaction mechanism between surrounding rock and initial supporting member is expounded.Based on the engineering geological conditions and physical and mechanical properties of surrounding rock of Pingdingshan tunnel,a finite element numerical model is established.(2)When the type of steel arch frame,the thickness of shotcrete and the spacing and length of anchor rods are unchanged,the initial supporting members with different spacing of steel arch frame are numerically simulated by using finite element software.The displacement,stress and plastic zone of surrounding rock caused by different working conditions are analyzed and compared.The results show that when the spacing of steel arch frame is between 0.8m and 1.0m,the variation of each index is small,considering the tunnel.For the economy of road construction,1.0m is chosen as the spacing value of steel arch in this project.(3)On the basis of the same spacing of steel arch,thickness of shotcrete and spacing and length of anchor rod,the numerical simulation of the initial supporting members of different types of steel arch is carried out.The results show that the change of the type of steel arch has little effect on the horizontal convergence of tunnel and the displacement of inverted arch uplift.When the type of steel arch is I20 b,the effect of restraining the settlement of arch roof is the best,so I20 b is chosen as the best one.The steel arch type of this project.(4)The finite element software is used to simulate the initial supporting members with the same type of steel arch,the spacing of steel arch and anchor rod,and the same length but different thickness of shotcrete.The analysis shows that the ability to control the horizontal and vertical displacement of surrounding rock is the best when the thickness of concrete is 25 cm.(5)On the basis of the same type of steel arch,spacing of steel arch,thickness of shotcrete and spacing of anchor rods,the numerical simulation of initial supporting members with different length of anchor rod is carried out.The analysis shows that the change of length of anchor rod has a significant effect on the vertical and horizontal displacement of tunnel.When the length of anchor rod is 4.5m,its performance is the best.(6)On the basis of the same type of steel arch,spacing of steel arch,thickness of shotcrete and length of anchor rod,the initial supporting members with different annular spacing of anchor rod are numerically simulated by finite element software.The analysis shows that when the spacing of anchor rod is less than 0.8m,the effect of controlling inverted arch uplift and horizontal convergence is remarkable.Therefore,0.8m is chosen as the spacing value of anchor rod in this project.(7)Comparing the optimized numerical simulation results with the monitoring and measuring data of Pingdingshan,it shows that the optimized numerical simulation results are slightly smaller than the monitoring and measuring results,and the optimized numerical simulation results are relatively safer and more reliable.