Model experiment and support optimization analysis of primary support arch cover excavation of large-section metro station in sandy mudstone stratum

The span and height of the Xietaizi metro station of Chongqing Rail Transit Line 18 are all larger than 20 m. The concept of “primary support arch cover” is adopted in the construction method, which aims to give full play to the bearing capacity of sandy mudstone, greatly improve the construction efficiency, and reduce the economic cost. In this paper, the model experiment of primary support arch cover excavation of large-section metro station in sandy mudstone stratum was carried out and the progressive failure process of the initial arch cover was revealed. It is found that the ground surface settlement is not strictly symmetrical about the station center, which is more significant in the case of the measuring points are far away from the central axis of the cavern. Since the support structure installed, the steel arch stresses and anchor axial forces at the inner and outer sides are in a rapid growth stage, and then shows a slow growth trend until stable. For the stresses at the inner and outer sides, the steel arch at the left arch shoulder is characterized by overall compression. The vertical displacements and convergence of the station are more prominent than the horizontal displacements and convergence, which indicates that the significance of control the settlement of the arch crown. The vertical convergence of the station is mainly caused by the settlement of the crown. When the level of loading is large, the number of longitudinal cracks will be increased as penetrating crack and the bulging phenomena will occur at the left arch shoulder of the secondary lining structure. Based on the numerical simulation, the whole dynamic procedure of construction is optimized from the demolition timing of temporary support. The vertical displacements and horizontal convergences for overall demolition schemes are smaller than those for stepping demolition with the excavation of middle guide holes.