An approach for calculating active limit support pressure of tunnel face of large-diameter pipe jacking in cohesive soils

Based on the method of limit equilibrium, an approach for calculating the active limit support pressure of tunnel face in cohesive soils is proposed. First, the failure mechanism of pipe jacking is studied by employing the numerical simulation. Then, an approach for the limit support pressure is derived and presented according to the failure mechanism. After that, the rationality of the approach obtained is verified by a numerical example of an actual project. Finally, influencing factors of the proposed approach are analyzed. Meanwhile the new method is compared with other methods, and the critical depth for deep and shallow pipe jacking is determined. The research results show that the failure mechanism of deep pipe jacking is horizontal cone mechanism, while that of the shallow one is wedge mechanism. The critical depth to distinguish deep pipe jacking from shallow one is 1.5 times the diameter. The proposed approach is rational and the calculation process is relatively simple, and it is suitable to actual projects. It can be used in homogeneous and layered soils, requiring the pipe jacking advancing in the same stratum. The limit pressure calculated by the new approach is larger than that by the limit analysis methods, however, it is almost the same when internal friction angle is close to 40 degrees.