Experimental study on large-scale subway station model considering adjustable water and soil pressure

To investigate the structural stress conditions during the excavation and failure stages of subway stations under adjustable water and soil pressures, a 1:10 scaled model was created based on similarity theory. Considering the equivalent soil pressure load, the loading procedures that controlled the excavation and failure of a metro station created via the cover excavation reverse construction method were evaluated. Additionally, an excavation unloading device and an external soil pressure-based graded loading device were developed for a metro station created via the cover excavation reverse construction method. By comparing the experimental results with the finite element simulation results, the axial force variations in the balance props during the excavation process were revealed, and the crack development process of the metro station was summarized. The external soil pressure remained unchanged; furthermore, the increase in the axial force of the balance props was negatively correlated with the distance to the previous balance prop and positively correlated with the axial force of the previous balance prop at the time of unloading. According to the graded soil pressure load and the corresponding crack initiation, development, and structural failure states, the model failure process was divided into four stages: the no-crack stage, initial cracking stage, crack penetration stage, and local damage stage. The first cracks in the station structure appeared at the corners and centers of the excavation openings. The first penetration of transverse cracks appeared in the middle of the basement first-floor wall. The cracks at the excavation opening corners and middle locations developed obliquely, forming an overall horseshoe shape. Localized damage first occurred at the corners where concrete spalled, exposing the reinforcement.