Field Investigations on Integrated Construction and Monitoring Technique for a Highway Tunnel Passing Through Soft Fractured Ground

Disasters such as collapse and water inrush are prone to occur when tunnel crosses the soft fault fractured ground. To settle the difficulties encountered in the construction of a highway tunnel crossing the F139 fault broken zone, the comprehensive advanced geological predictions, construction measures and real-time monitoring and measuring systems are conducted in field using tunnel seismic prediction (TSP), ground penetrating radar (GPR), three-bench seven-step method, 3D laser scanning technology, etc. The results demonstrate that the tunnel, starting from the mileage YK20+490, will get into the core influence zone of the F139 weakly fault broken zone. The development of the fractured structural surface and the water-rich condition are in front of the working face visually characterized based on comprehensive geological prediction. Ensuring that the tunnel passes through the F139 fault fractured zone with smoothness and safety, the implementation of comprehensive construction measures effectively curbs the occurrence of disasters of collapse and water inrush in tunneling. According to the comprehensive monitoring and measuring systems, the vault settlement and the horizontal convergence both show a sharp increase firstly, then remain a steady trend, followed by a slowly increase, and finally a stabilization. The maximum vault settlement and convergence displacements are 39.1 mm and 37.5 mm, respectively, which meets the allowable deformation specifications. After 15 days of excavation and support, the accumulated deformation of the surrounding rock shows a law of first increasing and then decreasing from the left wall to the vault to the right wall. The deformation near the vault is the largest with 21~23 mm, and the deformation near the side wall is the smallest with only 4 mm.