Research on the Dynamic Mechanical Response Characteristics of Foundation Pit Support Structures Under Loading and Unloading Conditions

The deformation and stress characteristics of foundation pit support structures are crucial indicators for assessing pit stability and safety. This study examined the internal forces and deformation of the support system during the simultaneous excavation and superstructure construction at the Guangzhou Xintang Metro Station deep excavation project. Through field monitoring and dynamic simulation， the mechanical responses of internal bracing， diaphragm walls， and slab covers to combined loads from superstructure construction， train operation， and earth excavation unloading were analyzed， and the pit’s overall deformation patterns were investigated. The results demonstrated that an “M”-shaped load pattern for simulating train dynamics better reflected real conditions compared to previous sinusoidal wave models， with simulations closely aligning with field measurements. Monitoring data analysis revealed three patterns in the horizontal displacement of the pile bodies： “forward-leaning”， “hill-type”， and “spindle-shaped”. Due to the transition in the support systems at the junction between the open-cut and cover-cut excavation sections， stress concentration occurred. Furthermore， the complex construction conditions of this project caused the location of stress concentration to shift between the corners of the pit and the midsections of the diaphragm walls.