| The tunnels in the Passenger Dedicated Lines offen are double track tunnels in order to solve the aerodynamics problems,the clearance area of these tunnels is above 100 square meters.The stability of the cutting face has rised to the most important factor of the security with the dimension increasing.This article has done following work based on Liuyang River Tunnel:1.It summarizes the experience of domestic and foreign tunnels with large section, and introduce the theory of the ADECO-RS approach.2. The research dicusses the face extrusion,plastic area,characteristic of collapse,surface settlement based on the numerical simulation with four types of dimension in the ground condition from II class to VI class,then summarizes the collapse types of the cutting face and offer a classification of the stability of the shallow tunnel with large cross section.3. The pipe-roof can not reduce the pre-convergence evidently without primary support or pre-reinforcing the advance core,so the cutting face is still not stabile.The fiberglass reinforced rock bolt and grouting could improve the strength and stiffness of the advance core,cut down the depth of the plastic area. The fiberglass bolt with grouting has much better effect than bolt used only to control the extrusion and plastic area.4. Suggest the pre-reinforcement method and parameters which is suitable for the large span Liuyang River Tunnel preliminary by contrasting the result before. Find the influence of the pre-reinforcement method on the face extrusion,convergence,surface settlement and the prime support by three-dimensional numerical simulation, then verify the previous result by model test to ensure the method and parameters is effective.It will meet many tunnels with large section in the Passenger Dedicated Lines, the stiffness of the advance core will increase evidently by the pre-reinforcement, and the face extrusion and convergence can be reduced,so enhance the security of construction.
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