Model test design to study the mechanical mechanism of side piles in a metro station constructed by the pile-beam-arch method.

[Objective] The pile-beam-arch (PBA) method, one among many metro construction techniques, is gradually gaining public favor owing to its unique advantages. These include superb structural stability and a remarkable effect on controlling surface settlement. At the same time, the side pile structure, a key mechanical component of the station, plays an important role in the success or failure of the projects involving PBA method. Most current research mainly focuses on the construction optimization and control countermeasures associated with the PBA method. However, there is a noticeable lack of studies focused on the mechanical behavior of side piles during construction and the principles governing side pile-soil interaction. [Methods] This paper focuses on a subway station project in the Guangzhou area, for which a simplified station model test method using the PBA method has been designed. Concurrently, this test method and numerical simulation have been employed to further investigate the evolution of the construction mechanics behavior of the side pile structure in different excavation processes of the station constructed using the PBA method. The primary focus of this study includes a comparative investigation into the soil pressure behind the piles and the internal force and deformation characteristics of the side piles under various spacing parameters. [Results] The results of this study are the following: 1) Under different pile spacing, stress concentration is most notable at the completion stage of the arch and the excavation stage of the first soil layer. As pile spacings increase, the stress concentration area behind the pile gradually shifts away from the pile position, with the stress peak decreasing correspondingly. 2) The bending moment of the side pile structure gradually increases throughout the construction process. The maximum section of the bending moment gradually migrates downward to the middle of the pile body, resulting in a "bow" distribution feature where the value is larger in the middle and smaller at both ends. Conversely, the axial force of the side pile structure remains relatively stable, presenting a "zigzag" pattern from the start to the end of the excavation. The maximum axial force appears at the junction between the side pile and the embedded stratum. 3) The peak value of the side pile's internal force increases with the pile spacings, and the pile spacings' influence on the side pile structure's axial force is more significant than its impact on the bending moment. As construction progresses, the lateral deformation of the pile body changes from initial "forward" deformation outside the station to final "bulging" deformation inside the station. The peak displacement of the pile body increases significantly with the pile spacing. 4) The stress and deformation of the side piles change most notably in the stage of excavation of the first soil layer. During actual construction, more attention should be paid to this stage, and appropriate lateral lining measures should be taken when necessary to maintain the stability of the station structure. [Conclusions] Through this experiment, the whole process of designing, making, operation testing, and data monitoring of the side pile structure in a metro station using the PBA method is demonstrated for students during the model test. This approach facilitates students' understanding of the mechanics and deformation evolution characteristics of a metro station constructed with the PBA method. [ABSTRACT FROM AUTHOR]