Mechanics of tunnel deformation in water-rich fault zone and double-gradient grouting NPR compensation countermeasures

Tabaiyi Tunnel is located in the eastern foothill of the Tibetan Plateau, crossing a multi-stage fault tectonic zone, and its surrounding rock is weak and broken, and its strength plummets when it encounters water. The peripheral rock under the original design scheme has a large deformation of meter scale, and there are disasters such as twisted arch, elevated arch bulge and sudden mud and water surge. In order to solve the problem of peripheral rock fragmentation in the tunnel in the water-rich fault zone, firstly, the deformation mechanism of the tunnel in the water-rich fault zone and its transformation were analyzed through mineral composition analysis, point load test and ground stress test; through the bearing capacity test of the grouted peripheral rock with ungrouted, regular grouted and double-gradient grouted, it was determined to adopt the double-gradient grouted process for the anchoring of NPR anchor ropes; then, the optimal anchor rope number was derived from the numerical simulation and on-site test; finally, through the on-site application, the optimal anchor rope number was obtained. Finally, the reliability of the double gradient grouting and high preload long and short NPR anchor cable support system is verified through field application. Based on monitoring data, the results of the study can be used as a reference for the control of large deformation hazards in similar tunnels with water-rich fault zones.