Study On Stability Of Tunnel Excavation Face For EBP Shield Machine In Double Ground

Shield was one of achieving full mechanization tunneling methods under tunnelconstruction. It was widely used for there were some advantages such as a smallimpact on the surrounding environment, a high degree of mechanization and tunnelforming quality. A reasonable choice of excavation face supporting force under shieldtunnel construction not only can ensure the stability of the excavation face, but alsocan effectively reduce the impact on the surrounding soil deformation and structures.When the shield machine went through the double-layer soil and there were somequite differences about the stiffness between the upper soft soil and the lying hard soil,the excavation face support pressure was more difficult to control than inhomogeneous soil. If improperly controlled, it can cause the surface subsidence toolarge or even a project accident. Therefore, there was an important theoreticalsignificance and engineering studies value to research the stability of shield tunnelexcavation face under double-layer soil. In this paper, the numerical simulation andtheoretical analysis was done to research the stability of the double shield tunnelunder double-layer soil, the main work was as follows:Numerical simulation of nonlinear analysis by software ADINA proceed wasdone. First, to verify the feasibility of the analysis software tunneling problems, thedesign and simulation program was compared with already existing literature.Secondly, the tunnel excavation model under double-layer soil was established on twoconditions,one is on upper soft and lower hard fomationd and another is on upperhard and lower soft condintion,obtaineding horizontal displacement in excavationface the center and the corresponding surface of the settlement. The limit supportforce was obtained by analyzing the variation of the excavation face support forcefrom the horizontal displacement of the center. Finally, the influence factors such asthe depth, the upper soil elastic modulus and internal friction angle on the excavationface limits supporting force was explored.Existing wedge model was summarized and Based on the limit equilibriumtheory the wedge model which was suitable for analysis of double formations wasproposed, and then the limit supporting force expression is solved by balancing theequation. The above model is extended to shield excavation of complex formation,and the excavation face supporting force formula was obtained for the analysis ofcomplex formation. When the upper soil layer was soft, the bottom of the sliding surface may occur at the boundary line of the two-layer soil, and part of theexcavation face instability failure was occured.Combined with the construction of a sectio n of the Guangzhou Subway,numerical simulations and theoretical model was analyzed, and the measured resultswas similar with engineering results. It proves that the numerical simulation methodand theoretical model is feasible, and can be used to analyze engineering problems.