Abstract:Taking the No.4 shield shaft with an excavation depth of 44.9 m and a diameter of 18 m in the Qingcaosha - Chenxing Reservoir Pipe Connection Project as an example, the foundation pit support design scheme and the confined water dewatering design scheme for ultra-deep shafts in soft soil areas are introduced. The deformation of the ground walls of the ultra-deep foundation pit is controlled by adopting a two-wall integrated composite wall structure and an inverted lining structure. By setting the ultra-deep N-Jet wall bottom horizontal sealing curtain combined with the ultra-deep ground wall and the ground wall joint waterstop, the confined water at the bottom of the pit ⑨ layer is isolated for the closed pressure reduction within the pit. MIDAS and Visual Modflow are used to establish the three-dimensional finite element numerical models to calculate the influences of foundation pit excavation and confined water dewatering in the ⑨ layer on the surrounding environment, ground settlement and deformation of viaduct pile foundation, respectively. The calculation results show that the above foundation pit support and dewatering schemes have little impact on the surrounding environment.
