| With the rapid development of national economy and the accelerating process of urbanization, the main way to solve the traffic problems of the biggest city is to develop the fast urban rail transit technology which has large capacity. Because of the rail transit project was subjected with the environmental constraints, there has been a lot of large span shallow weak geological engineering. As a kind of economic and effective auxiliary tunnel construction method, the advanced small pipe advance support method has simple construction process which is easy to operation, and it has safe construction progress as well as effects quickly, little loss of slurry and cost a little. This method is applied in many soft Geological Tunnel Engineerings. The in back filling tunnel of No.5 Rail Transit Line of Chongqing was used as engineering background, according to the site investigation, theoretical analysis, testing in laboratory, monitoring measurement and numerical simulation methods, the influence of the tunnel excavation process of small ducts in angle, ring to layout and vertical spacing and other factors on the stability of surrounding rock and tunnel face were studied systematically. The main research results are as follows:(1) The characteristics of backfill was analysis, the basic mechanical parameters of backfill soil was got through the indoor experiment, distributing the backfill gravel as soil by the plastic index and particle size. The classification of the backfill soil tunnel was got by analysis the condition of hydrogeological. The treatment measure of the backfill soil of tunnel was proposed. The safe and applicable and economic reasonable advance support scheme was obtained by the comparing.(2) The properties and parameters of backfill soil has been considered by using the MIDAS/GTS NX, which is a finite element software. The change law of the vertical surrounding rock plastic and tunnel vertical displacement of surrounding rock and the plastic zone of the tunnel face and surrounding rock was obtained by the simulation of tunnel excavation process and advanced small pipe reinforcement. Through the contrast of the small catheter and the simulation result of the two kinds of working conditions, the advanced small pipe grouting and reinforcement's influence on the tunnel face and surrounding rock stability was analysis complexly.(3) Through the single variable numerical calculation of the factors which influence the effect of the advanced small pipe advance support. Compared and analyzed respectively for various factors under different conditions of tunnel surrounding rock of vertical should force, vertical deformation of surrounding rock and tunnel face and surrounding rock plastic zone distribution were and obtained the small catheter in angle and ring to the size of the range of emplacement for the vertical surrounding rock deformation, influence of tunnel face and the stability of surrounding rock and the conclusion of large, small tube longitudinal spacing changes of tunnel face and surrounding rock stability influence smaller. Finally, optimized the design of the parameters on the impact of advance pipe reinforcement, making the small catheter method has higher practical economy in the underground engineering in the future.(4) Through the test of the fill the tunnel of 5101 standard of Chongqing Rail Transit Line of No. 5 and analysis of the monitoring data, the tunnel excavation process in horizontal convergence, vault subsidence, curve of ground surface settlement deformation law was obtained. Finally, through the comparing and analysis of the monitoring data and numerical simulation calculation results, the resort verified that the numerical simulation calculation results were quite identical with the actual monitoring value. |
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