Numerical Simulation Study on Applicability of Vertical Shaft Machine in Thick and High Permeability Silty Fine Sand
Scientific,rational and efficient development of deep underground space is an inevitable trend and an important problem in the continuous development of cities.Vertical shaft machine(VSM)is a new construction method for excavating ultra-deep shafts,which has a fast excavation speed and wide applicability.The shaft constructed by VSM is simple in structure,good in structural stress state,fast in construction,and has little disturbance to the surrounding environment,and can be widely used in point-like excavation for the utilization of deep underground spaces in cities.The first case of using VSM in the construction of the parking garage project of Nanjing Children's Hospital in China was used as a prototype,and a numerical model for excavating a 60 m shaft with VSM in sandy soil was established focusing on the deformation of the silty fine sand and the stability of the excavation surface.The results of the numerical model show that the surface deformation during the excavation of the 60 m shaft is controlled at the order of millimeter,and the maximum surface deformation do not exceed 13 mm.The safety factor is well controlled above 2.0 during the underwater construction process with a water level difference of 1 m.For the deformation problem,the uplift deformation of the bottom of the well and the surface deformation under different excavation depths were analyzed.And the safety factor of the excavation surface was calculated and analyzed related to the water level difference inside and outside the shaft and the depth of the shaft,which could guide the actual construction and realize segmented construction and refined control.
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