Abstract: The mechanisms and associated issues pertaining to catastrophic failures induced by pit collapse on adjacent existing tunnels require urgent in-depth investigation. This study investigates the impact of pit collapse on adjacent shield tunnel structures, with particular emphasis on establishing a numerical model based on the Coupled Eulerian-Lagrangian (CEL) method to examine the effects on different tunnel structural components under varying spatial configurations. Key findings reveal that: 1) Following localized failure of foundation pits, the load pattern of the adjacent tunnel structure changes, the internal forces of some joints in the tunnel structure exceed their corresponding bearing capacities, thereby compromising structural integrity; 2) Tunnel structural safety exhibits inverse proportionality to pit-tunnel proximity and direct proportionality to burial depth reduction, with bottom-positioned joints demonstrating the most severe performance degradation; 3) Practical mitigation strategies should focus on interrupting adverse effect transmission pathways through soil reinforcement or isolation measures implementation.