Parameters deterioration rules of surrounding rock for deep tunnel excavation based on unloading effect

How to ensure the construction safety is one of the key problems for the deep tunnel excavation. Since a tunnel excavation is an unloading process in essence, a novel method to accurately evaluate the damage evolution of the surrounding rock was conducted to study the deformation and failure mechanism of the tunnel by considering the unloading effect. A typical tunnel in Shimen Mine in China was regarded as the background, the three-dimension computational model was built by using FLAC3D technique. Then the different unloading zones of the surrounding rock were determined according to the unloading principle of tunnel excavation. The results show that the mechanical parameters for the different unloading zones, such as cohesion, internal friction angle, elastic modulus, and Poisson's ratio, display the nonlinear degradation characteristics. And it can be found that the increasing range of the mechanical response index, such as displacement, stress and force, increase about 0.73-2.10 times comparing the conventional analysis with the unloading calculation. The unloading effect has a great influence on the stress field, the displacement field, and the forces of the supporting during the tunnel excavation. So it is more practical to consider the unloading effect during the deep tunnel excavation. The conclusions obtained in the study are of important theoretical value to direct the similar engineering practice