Model test study on mechanism of continuous collapse triggered by local failure of shield tunnel

Recent shield tunnel projects have been witnessed frequent large-scale structural failures, yet comprehensive experimental studies remain scarce. This paper systematically investigates the internal force responses and failure mechanisms of tunnel structures following local segment failure through scaled physical model tests. The test employed a geometrically similar model, utilizing 304 stainless steel segments and custom-bonded joints to ensure joint strength equivalence to the prototype. Tests under varying burial depths are adopted to monitor structural mechanics using strain gauges, earth pressure cells, and laser displacement transducers. Results indicate that rings adjacent to the failure zone experience significant stress concentration due to soil arching, leading to a significant increase in the bending moments and displacements at the crown. The affected zone spans approximately twice the ring width. Local failure triggers soil arching, inducing force imbalance within the ring structure. This imbalance intensifies with outward springline displacement, ultimately evolving into progressive collapse. Greater burial depth exacerbates internal forces and deformations in adjacent rings. At a burial depth of 4D, peak earth pressure at the haunch of adjacent rings reaches 1.27 times the pre-failure value, with a bending moment increment exceeding 75%. It is recommended to enhance the safety factor in the design of deep-buried tunnels.