Mechanical Response and Deformation Evolution of Composite Linings with Prefabricated Inverts in Mining-Method Tunnels During Construction

To address the unclear relationship between overall deformation and local mechanical responses during the construction of composite linings consisting of precast inverts and cast-in-place arches in mining-method tunnels, this study takes Yaopocun Tunnel as the engineering case and uses field monitoring data from three typical cross-sections. Considering key construction stages, including invert segment assembly, base grouting, and casting of the secondary lining of the arch and walls, the spatiotemporal evolution of contact pressure between the invert and cushion layer, contact pressure between the secondary lining and primary support, reinforcement stress in the arch and walls, stress converted from concrete strain, and cross-sectional deformation is analyzed. The results show that variations in the contact pressure at the invert base exhibit temporal associations with construction equipment loading and subsequent secondary lining casting. The two types of interface contact pressure exhibited distinctly nonuniform distributions, with the mean monitored pressures during the later stage ranging from 30.39 to 36.47 kPa and from 52.67 to 85.16 kPa, respectively. In the later stages, the arch–wall reinforcement is predominantly under compression, with the absolute average compressive stress on the outer side being 1.32–1.99 times that on the inner side. Compressive stress is particularly pronounced at the wall feet. Although the strain-derived nominal stress responses of concrete were predominantly compressive, localized tensile responses were also identified, with a maximum calculated nominal tensile stress of approximately 2.34 MPa. The final crown settlement across the three sections ranges from 27.50 to 33.76 mm. Based on the normalized rate-of-change criterion, cross-sectional deformation entered a slowly varying stage approximately 4–5 days after invert excavation and rapid assembly, whereas interface contact pressure and lining material stress entered slowly varying stages approximately 24–40 days after subsequent secondary lining casting. These characteristic times were referenced to different construction events and do not indicate complete mechanical stabilization. These findings indicate that the overall deformation and local mechanical responses of composite linings with precast inverts exhibit distinct staged evolution patterns. A gradual stabilization of overall deformation does not necessarily indicate that subsequent adjustments in local mechanical responses have ended. During construction, attention should therefore be paid to stress variations at the wall feet and in localized tensile regions while controlling overall deformation.