Failure mechanism analysis and treatment of tunnels built in karst fissure strata: A case study

•Profound understanding of failure mechanism of tunnel in karst fissure strata is vital for safety.•The uneven failure form of tunnel was proposed focusing on the instability and prevention.•A new parameter reduction method of rock properties was used to revise the laboratory test results.•The discrete element method considering the influence of joints was used to reproduce the failure process. With the rapid increase of tunnels built in karst fissure strata, much more problems appeared during the construction process. Based on the Liangwangshan Tunnel, this article presents a case of tunnel failure by karst fissure, and the failure mechanism and treatment were analyzed. Firstly, when the karst fissure was close to the excavation face, A large area of cavity appeared above the right spandrel, which was distributed diagonally with a narrow shape. However, the pressure on the left side was greater than it on the right side near the karst fissure by on-site monitoring. Secondly, laboratory tests were carried out to determine that the karst fissure weakened the strength of surroundings, especially in shear and tensile strength. The results of theoretical analysis and discrete element method considering the joints indicated that karst fissure will exacerbate the uneven stress distribution and prevent the transmission of stress. The failure mode can be manifested as bending fracture and shear fracture, and the tensile shear composite failure mainly occurred on tunnel near the fissure. Finally, the radial grouting and advanced pipes have been implemented on site, and the on-site monitoring showed that the treatment measures were effective to control the failure when tunnel was excavating. The research can provide guidance for the similar tunnel engineering built in karst fissure strata.