In-situ monitoring and analysis of tunnel floor heave process

•An in-situ stress test was conducted to determine the tunnel floor heave process.•The reworking of a tunnel that experienced floor heave was monitored.•Three stages of stress progression are identified.•Three phases of floor heave are discussed.•The results can be used to inform floor heave control and retrofit measures. Given that the forces acting on the inverts of high-speed railway tunnels are complex and their proper accommodation is critical to traffic safety, an in-situ stress test was conducted on the concrete of a reworked invert in the Fuchuan Tunnel on the Lanzhou–Xinjiang High-Speed Railway. In order to study the forces acting on the invert and the associated development of tunnel floor heave, vibrating wire strain gauges were embedded in the reworked invert concrete. The results show that the reworked invert first underwent compression before tensile stress developed in the central region, then stopped increasing and balanced the compressive stress. Based on the in-situ test results, the floor heave of the invert can be divided into slight, moderate, and severe phases. The progression between these phases is associated with the recharging and infiltration of groundwater into the expansive rock beneath the tunnel invert with the release of load, subjecting the concrete above to sharply increased stress. This causes cracking in the invert, leading to increasingly severe floor heave. The results of this study are of significance for the optimization of tunnel design and support systems and can be used to ensure tunnel traffic safety.