Field Test and Analysis of Mechanical Characteristics of Tunnel Invert Structure for High-Speed Railway

The mechanical characteristics of tunnel invert for high-speed railway are complex and crucial to the operation safety for high speed train. In-situ stress tests were performed on the concrete and rebar of Fuchuan tunnel invert after being reworked on the second double-track of Lanzhou-Xinjiang Railway. The mechanical characteristics and stress change rule of concrete and rebar in invert structure were analyzed. Results showed that under the action of the dead weight of tunnel secondary lining, the load of upper surrounding rock, the expansion of surrounding rock on tunnel base, track roadbed and train load, the reworked concrete in tunnel invert experienced a change process of compression, local tensile stress and stable tensile-compressive stress. The maximum tensile stress of concrete and rebar in invert structure appeared at the upper part of invert center. The maximum tensile stress and compressive stress of concrete was 1.9 MPa and 8 MPa respectively during the whole course from invert reconstruction to tunnel operation. After a large amount of groundwater was added, a large amount of load was released from the expansion of surrounding rock on tunnel base, which made the concrete stress, rebar stress and earth compressive stress increase rapidly. Based on geological conditions and monitoring results, the floor heave of Fuchuan tunnel invert was divided into 3 degrees: mild, moderate and severe. Corresponding control measures were given for each degree of floor heave. © 2017, Editorial Department of China Railway Science. All right reserved.