Deformation and damage assessment of segmentally designed tunnel under normal fault dislocation

Abstract

Segmental design is an effective measure for mitigating tunnel damage under normal faulting. In this study, to assess disaster mitigation levels based on the deformation and damage behaviors of segmentally designed tunnels, three numerical models with varying segment-lining lengths were established, and compared with a large-scale model test. Findings indicate that the segmentally designed tunnels exhibit a step-like longitudinal deformation pattern, and 6 m long segment linings outperform 12 m linings. The peak stresses at the tunnel crown and invert for 6 m linings decreased substantially compared to those for 0 and 12 m. The volumes of tension damage elements for damage values exceeding 0.9 for 6 m linings were substantially less than those for 0 and 12 m. In the model test, the segmentally designed tunnel displayed a step-like deformation pattern, consistent with the numerical simulations. Longitudinal bending of the tunnel was indicated by the maximum longitudinal compression and tension strain measurements. Segment linings damage in the normal fault zone manifested as longitudinal cracks and dislodged blocks in the crown, invert, and arch waist areas, consistent with the numerical simulation. Segmental design prevents complete failure, but localized lining damage is experienced through the redistribution of the longitudinal displacement and release of fault energy, resulting in only slight lining damage. The segment lining damage volumes for segments 6 m long were substantially less than for tunnels without joints. Considering that high-grade tunnel linings often use form jumbo construction with form jumbo lengths ranging from 6–12 m, it is recommended that the segment lining length for tunnels crossing normal-fault sections be set to 6 m.