Thermography analyses of rock fracture due to excavation and overloading for tunnel in 30° inclined strata

Large-scale physical model test of 30° inclined strata was conducted to investigate the damage mechanisms during the excavation and overloading using infrared detection. The experiment results were presented with thermal images which were divided into three stages including a full face excavation stage, a staged excavation stage, and an overloading stage. The obtained results were compared with the previously reported results from horizontal, 45°, 60°, and vertical strata models. Infrared temperature (IRT) for 30° inclined strata model descended with multiple fluctuations during the full-face excavation. For the staged excavation, the excavation damage zone (EDZ) showed enhanced faulting-like strips as compared in the 45°, 60°, and vertical models, indicating the intensified stress redistribution occurred in the adjacent rock mass. In contrast, EDZ for the horizontal strata existed in a plastic-formed manner. During the overloading, abnormal features in the thermal images were observed preceding the coalescence of the propagating cracks. The ultimate failure of the model was due primarily to the floor heave and the roof fall.