Analysis On The Stability Of Surrounding Rock In The Excavation Process Of Nianla Moutain Tunnel

In this paper, elasticity theory and surrounding rock pressure theory which have been mature currently was adopted based on the background of Nianla Mountain Tunnel. The mechanical behaviour of the existing lining and excavation designs for four-grade and five-grade rock in Nianla Mountain Tunnel was analysed in the simulation of the construction process by FEM. On the base, the cross section designed for the five-grade rock of the tunnel was optimized. The optimized design has the same lining structure and excavation scheme with the five-grade rock tunnel. The construction process of it was simulated with FEM. The mechanical behaviour and the calculation result of the design for the five-grade rock tunnel and the optimized was anaysed and compared. The main contents of this paper are as follows.1. Five types of shed-tunnel structure were analysed, and the development prospect, the advantages and disadvantages of shed-tunnel were discussed.2. According to the construction principles and the construction steps, the whole construction precess of a shed-tunnel was simulated with Finite Element Method and its relavant software.3. According to the characteristic feature of shed-tunnel and ground structure, the sesmic response of several types of shed-tunnel was analysed with the unified viscous-spring boundary for static and dynamic analysis. On the base, a rational aseismic structure form was proposed.4. The 3-D finite element modal of the connection part of a tunnel and its shed-tunnel was built. The relationship between the seismic response and the joint type in the shed-tunnel and the hidden hole under seismic load was studied.Based on the above calculation and analysis, following conclusion was given.1. Five types of shed-tunnel structure were analysed, and the development prospect, the advantages and disadvantages of shed-tunnel were discussed.2. According to the construction principles and the construction steps, the whole construction precess of a shed-tunnel was simulated with Finite Element Method and its relavant software.3. According to the characteristic feature of shed-tunnel and ground structure, the sesmic response of several types of shed-tunnel was analysed with the unified viscous-spring boundary for static and dynamic analysis. On the base, a rational aseismic structure form was proposed.4. A comprehensive comparison of the excavation simulation results gotten from the optimized tunnel and the original five-grade surrounding rock tunnel was made. And a conclusion was gotten that the mechanical stability of excavation and the lining performance of the optimized tunnel section is better than that of the original design.5. The economic benefit of the tunnel optimized is better than that of the orginal design.