Modeling the Behavior of Shallow Continuous Tunnels Subjected to Active Dip-Slip Faults

In today's modern world, the performance of tunnels is crucial as one of the most vital urban infrastructures. Faults are one of the most significant and influential geological factors that have led tunnel designers to strive to eliminate them as much as possible and use alternative routes instead. However, this is often not feasible, and tunnels inevitably encounter faults. Therefore, engineering examination of ground behavior and potential hazards related to tunnel construction is essential to significantly reduce risks and dangers arising from encountering faults during excavation and operation. In this research, various scenarios of the dip-slip fault upon encountering a continuous tunnel have been modeled and evaluated using FLAC^3D software. In this respect, information from four centrifuge laboratory tests with different specifications and parameters has been utilized for validation. The validation results show that the error obtained from the numerical modeling results is generally acceptable, with one exception. This indicates that the method aligns well with the experimental results. The maximum error is related to the collision of the normal fault with the thick tunnel, which this number is equal to 28 percent. Also, observations show that as the height of the overburden decreases relative to the tunnel diameter, the vertical displacement of the fault increases by 9–23 percent and a larger area of the ground surface becomes involved with the sinkhole due to the shallow depth of the tunnel. Numerical methods state with good accuracy that under similar conditions, a continuous tunnel dealing with different angles of the normal fault is more susceptible to collapse hazards compared to experiencing a reverse fault, and more special attention should be paid to it. But, in general, by reducing the ratio of the (h/D) and increasing the fault angle up to 70°, the tunnel fragility reaches its highest level, and it may lose its performance completely.