Soil Mass Stability at the Working Face of a Rectangular Pipe-Jacking Tunnel with a Large Section
(1 College of Civil Engineering, Inner Mongolia University of Science and Technology, Baotou 014000;2 College of Mathematical and Biological Engineering, Inner Mongolia University of Science and Technology, Baotou 014000;3 Baotou Urban Construction Group Ltd.,Co., Baotou 014000)
Abstract：
Based on an underpass project at the Inner Mongolia University of Science and Technology, which was constructed with an earth pressure balance rectangular pipe-jacking machine, the active and passive failure laws of the excavation face of the rectangular jacking pipe in sand and gravel are studied using theoretical analysis, numerical simulations, and site monitoring. The following conclusions are determined: 1) in light of the characteristics of rectangular sections, a trapezoidal wedge calculation model is set up, a calculation formula for extreme support stress during active failure of the tunnel face is derived and applied in a practical project, and the limited support pressure calculated by the above formula is determined to be very close to that of the numerical simulation, so the two methods are verified; 2) the form of the ground surface settlement trough simulated by FLAC3D is similar to the measured ground settlement trough, which approximately complies with a normal distribution and is very close to the ground settlement value; 3) with a decrease of the support stress ratio, the plastic zone of the excavation face develops from the front of the face to the inclined top. When support stress ratio is 0.165, the soil horizontal displacement in front of the excavation face suddenly increases, the plastic zone extends to the ground surface and active failure occurs with a loss of overall stability. The development pattern of the plastic zone at the surface after excavation face failure resembles a trapezoidal wedge shape, so the rationality of the calculation model is verified; and 4) with an increase of the support stress ratio, the plastic zone in front of the excavation face develops from the face top to the inclined top and reaches the ground surface, resulting in instability of the soil mass with passive failure occur? ring when the support stress ratio is 3.0, and the plastic zone is much smaller than that of active failure.
2017, Vol. 54 