| Pipe roof reinforcement technology is one kind of economical and practical auxiliary construction methods, and it played a major role in the shallow depth tunnel excavation. Pipe roof reinforcement technology has many advantages such as reinforcing the surrounding rock, improving the level of tunnel surrounding rock and its performance of anti-permeability, enhancing the stability of excavation face, and controlling the settlements of the ground. This paper took the force and displacement of pipe roof and the stability of tunnel face as research object, which was based on the program of Beiyinpo tunnel in Guizhou. It had deeply and systematically researched on the mechanical model of pipe roof advanced support, the action effect of pipe roof advanced support, and the influence factors of action effect, which were considered as the reasons this paper optimized the designing of pipe roof support eventually. The main research contents and results are as follows:① It established the pipe roof mechanical model, which applying Pasternak double-parameter elastic foundation beam theory based on the interaction relationship between pipe roof advanced support and surrounding rocks. It put forward a solution to solve the internal force of pipe roof, which was based on finite difference method, and derived the deflection equation, stress and strain calculation formula of pipe roof through analyzing the load on pipe roof. It also established stability analysis method of tunnel face based on equation of foundation reaction, which was applied to derive the calculation formula for the limit support force of tunnel face within pipe roof advanced support.② This paper obtained a series of monitoring test data such as displacement of vault, convergence of tunnel surrounding, deflection of ground surface, and variation law of stress and strain within pipe roof advanced support by monitoring the Beiyinpo tunnel of Shanghai-Kunming line located in Guizhou, and also obtained the mechanical characteristics and action mechanism of pipe roof advanced support during tunnel excavation by analyzing the data thoroughly.③ This paper applied finite element software MIDAS/GTS NX to establish finite element analytic model of Beiyinpo tunnel under the support of pipe roof, and compared the different laws of tunnel face and surrounding plastic zone, internal force of steel pipe, spatial deformation of tunnel between the two situation of with and without the pipe roof. In addition, it compared the calculation results with monitor test, proving that the pipe roof can efficiently inhibit displacement of ground surface and vault, enhance stability of tunnel face and surrounding rocks within the shallow buried bias condition.④ This paper systematically analyzed four kinds of influence factors to pipe roof advanced support like pipe diameter, ring spacing, excavation distance, and length of pipe roof, and it established plants of numerical models with just one parameter and in different conditions at the same time, calculated all kinds of conditions, whose results were related to tunnel face stability like tunnel face and surrounding rocks plastic zone, internal force of pipe roof, and tunnel spatial deformation, obtained the influence degree of each parameters working to the effect of pipe roof advanced support. At last, it optimized all parameters that researched in this paper, making pipe roof method more economy and more efficiently in the real underground engineering in the future. |
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