Abstract
Loosening of earth pressure by tunnels is an important parameter for the structural design of subway stations, this study analyzes the difference between the loosening pressures of each span of a shallow multi-span tunnel station using the pile-beam-arch (PBA) method. By conducting a similarity model test of the PBA method, we simulate the complete excavation process. We study the sliding failure mode of the overlying soil of the shallow-buried station and the law of change of the loosening pressure of each span. A simplified calculation model for the loosening pressure of shallow buried multi-span tunnels by the cavity pile method was developed, and the applicability of the formulae and sensitivity analysis of the parameters were carried out. The results reveal that the loosening pressure of the mid-span is transferred to the stress of the side-span during tunnel excavation. This finding contradicts Terzaghi’s and Bierbaumer’s methods, which do not consider the influence of tunnel structure on the loosening pressure of the overlying soil. The side span relaxation pressure is only related to the soil capacity and the depth of burial of the tunnel This research can provide an important theoretical reference for the design of the overburden load and lateral confining pressure of the PBA structure design.