Stability Study of Shield Tunnel Excavation Face Induced by Shield Chamber Pressure En-tering in Shallow-Buried Sand Stratum
[Objective]Solve the problem of excavation sur-face stability during shield tunneling with pressure entry in shallow-buried sandy stratum.To solve the problem of the sta-bility of tunnel face of shield tunnel with pressure into the chamber in shallow buried sandy soil stratum.[Method]The limit support pressure during the shield tunneling pressurized chamber entry operation is studied by combining numerical simulation,theoretical analysis and engineering verification methods.Firstly,the active failure phenomenon of shallow-buried sandy soil stratum is studied by numerical simulation,and the corresponding limit support pressure and failure zone shape are obtained.Then,based on the numerical simulation results,the failure mode applicable to shallow-buried sandy soil stratum is constructed,and the corresponding ultimate sup-port pressure is solved.Finally,the model is applied in the Hangzhou Metro Line 5 pressurized inlet project,and the ground settlement is monitored.[Result & Conclusion]The limit support pressure increases approximately linearly with the increase of burial depth,and decreases approximately exponen-tially with the increase of internal friction angle;the instability mode of the shallow-buried stratum presents the shape of lower wedge and upper inverted cone/platform,in which the upper failure zone is further split into the damage core zone and dis-turbance zone.By comparing with the numerical model and the literature model,it is found that the proposed wedge+invert-ed cone/platform model can better describe the phenomenon that the damage zone can reach the ground surface due to the inability of the shallow-buried sandy stratum to form an arch;during the shield pressure entry construction of Hangzhou Met-ro Line 5 project,the maximum ground settlement value caused is 9.5 mm,and the influence range is within 10 m on both sides of the tunnel axis.
metroshallow-buried tunnelsandy soil stra-tumshieldexcavation stabilityboarding under pressurelimit equilibrium method
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