Study On A Subway Shield Tunnel Under The Excess Pore Pressure By High-pressure Jet Grouting

This study based on an engineering instance that high-pressure rotary jet piling caused the breakage of an adjacent subway shield tunnel. How to estimate the lateral force induced by high-pressure jet grouting, how to control the deformation of subway tunnel effectively, and how to insure the safety operation of metro line were the leading propositions in this thesis.In view of foundation reinforcement mechanism, the study compared high-pressure rotary jet piling with static piling from the point of view of soil stress distribution. Pile area equivalent modulus "m" was introduced. According to elastic and plastic soil mechanics and Vesic cavity expansion theory, two theoretic formulas were put forward, which embedded the parameters "m", to account for the increment of soil horizontal stress and excess pore pressure.The FEM model of shield tunnel lining under additional lateral pressure was built using SAP2000. Evaluate a series of value of lateral pressure and get corresponding tunnel lining deformation. Then the relationship between lateral force and lining deformation could be figured by a great deal of curves. Contrasted with construction monitoring data of lining deformation, the factual lateral pressure could be ascertained.Adopting the factual lateral pressure, the parameters, "m" within theoretic formulas and " K " and " n " within experiential formula, could be fixed by displacement back analysis method. The experiential formula is used widely to work out the pressure attenuation of high-pressure jet stream. Two curves which described soil lateral pressure attenuation were drawn according to the theoretic and experiential formula respectively. The outcome figured out that, in precondition of fixing the parameter "m", a high-pressure rotary jet pile with section S could be regarded as a static pile with section mS when its extrusion effects to be investigated. And that the theoretic formulas are adapted to estimate the extrusion effects of ground by high-pressure rotary jet piling.In the finality, several optimizing measures of high-pressure rotary jet piling were suggested to restrict the displacement of shield tunnel.