Study On Deformation And Bearing Performance Of Supporting Structure For Extra Large Span Tunnel

The total mileage of China's high-speed railways is increasing year by year.In the process of high-speed rail construction,due to the influence of topography and geomorphology and other factors,sometimes we need to build large span and large cross section tunnel to meet the needs of train traffic.In the process of building an extra large span tunnel,how to guarantee the sufficient bearing capacity of the supporting structure and the stability of the surrounding rock is the most important thing to ensure the safety of the tunnel structure,and it is also an urgent problem to be solved in the scientific research.In this paper,the deformation characteristics,stability of the tunnel and surrounding rock and the bearing capacity of the combined arch and secondary lining of the tunnel structure are studied through investigation and analysis,numerical simulation and analytical derivation.The main work and research results are as follows:(1)By selecting different buried depth and span,the stress and deformation of the tunnel are analyzed.The calculation results show that with the increase of the span and depth of the tunnel,the structural deformation and the scope of the plastic zone of the surrounding rock gradually increase;pre-reinforcement within 120° above the vault of the four-line tunnel can reduce the settlement of the vault of the tunnel by 30%,however,the effect of controlling the side wall convergence is not obvious.(2)The stability of the surrounding rock is studied,and it is concluded that the four line tunnel should be supported before the stress release up to 75%.It is suggested that the reserved deformation of the four line tunnel of grade IV surrounding rock is 120?160mm.It is studied that the side wall and the inverted arch are applied at different time and the steel frame and the shoterete applied at different time.The results show that the different supporting time will have a great effect on the deformation of the tunnel.When the concrete begins to give full play to the support,the settlement of the vault quickly reaches stability and no longer grows,and the deformation of the hole is basically ceased to continue after the back arch begins to play the supporting role.(3)The load-bearing capacity of composite arch composed of system bolts,prestressed anchors and surrounding rock,and the bearing capacity of lining are studied,and the formula for calculating the bearing capacity of composite arch structures is deduced.Based on the Xiabeishan tunnel,the derived formula is programmed by MATLAB,and the bearing capacity of composite arch structure,lining and compound arch structure is calculated when many parameters are changed.The pressure arch is simulated.The inner boundary of the pressure arch is 7.2m above the vault,and the outer boundary is 18.4m above the vault.The length of the prestressed anchor can be 10 meters.(4)According to the measured data of the load on the secondary lining of several tunnels in China,the bearing proportion of the secondary lining is mainly distributed between 3.5%?87%,and the side pressure coefficient is mainly distributed between 0?4.For the secondary lining,it is recommended to control the support time and ensure that the load ratio of the secondary lining should not exceed 70%.When the lateral pressure coefficient of the secondary lining is between 0 and 1,the secondary lining is in a safe state.When the lateral pressure coefficient of the secondary lining exceeds 2,it is suggested to reinforce the foot of the wall to prevent this part from being damaged.