Effects of fissure properties on the tunnel damage evolutions:Insights from DIC-based 3D printing experiments and meshless numerical simulations

Unknown pre-existing fissures have great impacts on the failure modes and mechanical properties of tunnels. However, there are few discussions about the influence of different fissure properties on the tunnel damage morphologies. Based on this background, three-dimensional (3D) printing technology is utilized to prepare the arch cross-section tunnel with different fissure azimuthal angles and inclination angles, and the failure processes are investigated by Digital Image Correlation (DIC) technology. Meanwhile, traditional Smoothed Particle Hydrodynamics (SPH) momentum equation is improved to simulate the progressive failure processes of the tunnel model. Results show that: There are mainly three crack forms around the tunnel: Upper side crack, lower side crack and lower main crack, and two crack forms exist around the pre-existing fissure: Wing crack and anti-wing crack. Upper side cracks and lower side cracks appear in all specimens, but lower main crack does not always appear. The propagation length of the wing crack and anti-wing crack increases with the increase of the fissure deviation from the axis of the tunnel. The stress-strain curves of the tunnel specimens present four typical stages: Initial compaction stage, linear elastic deformation stage, elastoplastic deformation stage and post-peak stage. The peak strength of the specimen decreases first and then increases with the increase of fissure azimuth angle beta, however, it has little change under different fissure inclination angle alpha. Finally, the crack initiation and propagation mechanisms are discussed. The research results can provide some references for the correct understandings of the influence of unknown pre-existing fissures on tunnel failure modes and the applications of SPH method into tunnel failure mechanisms.