Experimental study on the mechanical behavior of utility tunnel with flexible joints passing through active thrust fault

The mechanical response law of underground utility tunnels passing through active faults is complicated, and the structures suffer severe damage. An experimental model test with a scaling ratio of 1:30 has been designed to simulate thrust fault dislocation with the 45° dip angle. Through the monitoring and analysis of the lining structure vertical displacement, strains, contact pressure, and failure patterns, the mechanical behavior of the utility tunnel structure with flexible joints passing through the active thrust fault with the 45° dip angle is investigated. The results show that the compression failure occurs mainly in the joint area of the segmental lining. The surrounding rock forms a triangular shear zone as a result of thrust fault displacement. After the fault dislocation is completed, the longitudinal direction of the tunnel is bent into a Z-shape, forming a compression zone and void zone near the fault trace to accommodate the displacement of the thrust fault. The cracks, fragments of concrete peeling off and dislocations are mainly concentrated in the vicinity of the fault trace; especially, the segments B–D are the most damaged. The three segments B, C, and D appear to have an obvious dislocation at the flexible joint, and the average displacement is 6.9 mm (actually 0.207 m) and 4.3 mm (actually 0.129 m). The maximum tensile and compressive strains are distributed in 3# with values of1716.5 με and − 1182.6 με, respectively. Compression and tensile failure occur. The segments with flexible joints improve the overall anti-disconnection performance. When the thrust fault displacement exceeds 50 mm (actually 1.5 m), the damage length of the lining structure within the hanging wall and the footwall is 3.5S (S is the maximum span of the tunnel) and 2.4S, respectively.