Research On The Blow-out Failure Face Pressure Of Trenchless Shallow Tunnel In Sand

21st century is development and utilization of underground space’s century. Faced with ever worsening problems of resource shorage and environmental pollution, utility tunnel is an efficient way to solve the problem of underground utilities shortage, unified regulation deficiency, repetition of the infrastructure costruction. It can promote the efficiency of planning, constructing, using, managing and sharing underground space resources, and is one of the fundamental tasks for modern urban management. In the construction of utility tunnel, shield is used most frequently. In shallow tunnel, too large support pressure may lead to the upheaval of ground surface, even blow-out failure of excavation face. Hence, this study research the estimation of the required support pressures and the passive failure mechanism. This study improves the evaluation of the upper limit support pressure for the blow-out failure and the relevant theoretical foundation is cemented.To solve the problem of face stability of shallow tunnels in sand, firstly, the partial blow-out failure of excavation face from the point of view of upper bound analysis is obtained according to the former literatures. A 2D kinematically admissible mechanism for the partial blow-out failure is proposed, and then the optimal pattern of partial blow-out failure is discussed. The ultimate support pressure for partial blow-out failure is also obtained using the upper bound analysis.Secondly, based on the lack of previous chapter, A 3D kinematically admissible mechanism for the partial blow-out failure is proposed, and then the optimal pattern of partial blow-out failure is discussed. The ultimate support pressure for partial blow-out failure is also obtained using the upper bound analysis.A finite differential program(FLAC3D) is chosen for numerical analysis. The analysis results of a large number of cases reveal that passive failures are often occurred on shallow tunnels. The passive failure mechanism is also studied in this chapter.In conclusion, the 2D,3D and numerical method can well predict the passive failure pressure in sand, which can provide reference for determining upper support in construction of shield driven tunnels.