Objective The permanent-temporary combined construction technology takes the support structure as a permanent one to jointly bear loads, without dismantling or replacing struts. Its mechanical development pattern differs from that of traditional methods. To ensure engineering safety, it is necessary to clarify the mechanical development law of underground stations constructed using this technology.

Method Taking a permanent-temporary combined underground station in Jinan City as the research subject, sensors are added during construction, and monitoring data are used to investigate the mechanical development throughout the entire construction process. A finite element model is established to study the stress characteristics of the composite structure, and a combined prediction model is employed to predict the internal forces of the main structure, proposing further a reliable data prediction mode.

Result & Conclusion  The side walls mainly exhibit tensile behavior on the outside of the excavation pit, with the top of the B1 side wall and the bottom of the B2 side wall being identified as critical points. The key engineering stage of the base slab is the water-level recovery stage, during which its bending moment is primarily induced by water loads. The intermediate slab remains stable after construction completion, with its bending moment mainly generated by the self-weight of concrete. The key engineering stage of the roof slab is the soil backfill stage, where its bending moment is primarily caused by the self-weight of concrete and backfill loads, showing a significant increment. The combined model effectively reflecte the bending moment development pattern of the side walls during construction, demonstrating higher predictive accuracy than that of individual models.