Study on the structural catastrophe mechanism and disaster mitigation strategies of a double-compartment underground utility tunnel under the creep-slip dislocation of reverse fault

Fault creep-slip dislocation and seismic effects can cause significant damage to underground structures that are shallowly buried and cross faults and their overlying soils. This study investigates the seismic performance of a segmental double-compartment utility tunnel crossing a 45° reverse fault. Through a 1:30 scale model test incorporating a novel disaster mitigation strategy—flexible joints and damping layers—we assessed the structure's real-time response to fault creep. This approach enables the elucidation of the disaster mechanism and the assessment of the disaster mitigation effect of setting up protection under the fault creep-slip dislocation. The findings indicate that flexible joints are more effective in dissipating the energy and forced displacement generated by fault creep-slip misalignment. This, in turn, reduces the bending-shear composite action applied to the structure. The adjacent sections of the segmental lining structure exhibit minimal degradation, with local damage restricted to the joints of blocks C-E. This mitigates the risk of complete structural collapse. A discernible displacement change has been identified in the underground utility tunnel structure situated within the Hanging Wall area. The internal force response of the double-compartment underground utility tunnel structure in close proximity to the fault surface is noteworthy, particularly the damage observed in the underground utility tunnel structure within the range of 70–120 cm, which should be regarded as a critical defensive area. Subsequent to the execution of the inverse fault misalignment, the double-compartment underground utility tunnel structure becomes vulnerable to tensile and compressive damage. The predominant forms of cracking damage include cracks, inter-ring misalignments and the spalling off of blocks. The occurrence of fault misalignment gives rise to the movement of the overlying soil layer towards the surface. This process ultimately results in the formation of through cracks and substantial damage to the surface at a specific depth within the hanging wall. The deformation of the soil can be classified into three distinct zones: the hanging wall stability zone, the deformation zone, and the footwall stability zone. Ensuring the stability of the ground structure is imperative. It is therefore imperative to avoid these zones as much as possible. Moreover, it is recommended that a safe distance be maintained from the deformation zone on the surface. The deformation zone of the overlying soil layer is subdivided into three distinct zones. The aforementioned zones are designated as Zone I, Zone II and Zone III. The perimeter of the soil body in Zone II is delineated by an inverted triangular configuration, which is designated as the shearing zone. It has been demonstrated that the implementation of flexible joints can effectively enhance the fracture-resistant performance of underground structures by safeguarding the passage following an earthquake.