Study on the mechanical behavior of utility tunnel structure considering flexible joints under reverse fault dislocation

To study the mechanical behavior and failure mode of utility tunnel structure with flexible joint disaster mitigation measures under the reverse fault dislocation, a method combining 1:30 reverse fault model test and numerical calculation analysis was adopted. The structural displacement, strain, contact pressure between the utility tunnel and the surrounding rock were analyzed in details, as well as the breaking process under the action of 45° reverse fault dislocation. The mechanical behavior and failure mode of key parameters of the utility tunnel structure considering flexible joints under the action of 45° reverse fault dislocation were revealed. The results show that the degrees of responses and damage of the utility tunnel structure considering flexible joints in the hanging wall are more excellent than those in the footwall under the reverse fault dislocation. After the fault dislocation is completed, the overall structure of the utility tunnel is S-shaped along the axial direction. The top plate of the B-D block utility tunnel structure exhibits an evident continuous dislocation phenomenon, and the bottom plate is crushed. The failure modes of the utility tunnel structure include three types of cracks (longitudinal and oblique cracks), concrete peeling, and steel wire exposure. The top plate of the utility tunnel structure in the upper and lower walls is subjected to positive and negative bending moments, respectively. The bottom plate is subjected to negative and positive bending moments. The structure is in an eccentric stress state. A 4-level damage degree scale is established based on the damage factor: no damage, slight damage, moderate damage, and severe damage. The assessment found that only minor and moderate damage occurred in localized areas such as the joints of the integrated pipe gallery structure with flexible joints, and no areas of severe damage were observed. The use of flexible joints can effectively absorb the forced displacement and internal force exerted on the structure by the fault dislocation and improved the safety of the utility tunnel structure passing through the fault. The test and simulation analysis results could guide similar tunnel projects across active faults. © 2023, Central South University Press. All rights reserved.