FACE STABILITY OF SHIELD TUNNEL WITH DIFFERENT SUPPORT MODELS IN SAND

Setting reasonable support pressure for different support model shield tunnel machine is extremely important for the face stability of the shield tunnel. The face stability is discussed respectively when the face is above and under water for the typical distribution of face support in tunneling by compressed air shield, slurry shield and EPB shield. The research results show that, When the effective support stress is uniformly distributed, the soil mass is unstable in the middle and the bottom of the face except for the instability in the lower part of the clay face; when the effective support stress is distributed in trapezoid with a small top and big bottom, the soil mass is unstable in the top of the face except for the instability in the lower part of the soft clay face; on the contrary, the lower half part of the face is instable for all kinds of soil mass when the effective stress distribution is in trapezoid with a big top and small bottom. In the balanced support mode of compressed air shield, slurry shield and EPB shield, the face has already gone through local instability before the overall instability of face assumed by the wedge-shaped model; therefore, traditional wedge model based on overall stability is unsafe. Furthermore, in order to facilitate the calculation of active earth pressure, active pressure coefficient and others design parameters are also provided as function of the soil friction angle and the friction between cutter and the soil.