Study Of Blow-out Failure Mechanism And Limit Supporting Force On Tunnel Face In Shallow Metro Tunnel

The face stability of shallow shield tunneling is one of the most important research. In the past, the problem may depend on traditional finite element method which pay more attention to the stability of the destruction process. However there is other methods called limit analysis method which fix on the state of the final destruction. Now, the limit analysis method has two main directions. One relys on assumed rigid block failure modes, the other is the limit finite element method. This paper mainly use the two methods to get the answer of the face stability in shallow shield tunneling. The main contents are as follows:(1) based on the assumed face stability failure modes, we constructed the corresponding velocity field and get the upper bound method of limit analysis result. Then, by programming calculation we analyzed the problem of the shallow shield tunnel face stability.(2) According to the upper limit finite element method, the established face stability failure modes shallow shield tunnel were analyzed. Calculation results is verified with the two-dimensional case of the rigid block method.(3) The three-dimensional failure modes is used to settle the problem of face stability, we calculated and obtained the corresponding calculation chart, and the result is consistent with the literature.(4) Limit analysis method is used on a specific project examples, we calculate the corresponding limit support force, and draw the corresponding failure modes, then we analysis the stability of the damage characteristics. And also we acquired the result by FLAC3D.(5) The different failure characteristics of different depth、cohesion and friction angle is discussed though the program of simplified three-dimensional failure modes.