Numerical Simulation Study on the Mechanical Properties of the Surrounding Rock in Tunnel Boring Machine Inclined Shaft

The surrounding rock of a Tunnel Boring Machine (TBM) inclined shaft can be disturbed after excavation, accompanied by significant changes in mechanical properties.The safety of the inclined shaft is directly affected by the stress and displacement changes of the surrounding rock at the vault and haunch areas in the vertical section.To determine changes in stress, displacement, and plastic zone of the surrounding rock in the vertical section of the inclined shaft, a numerical simulation study was conducted based on the FLAC3D finite difference software.Accordingly, the effects of buried depth (H), lateral pressure coefficient of surrounding rock (K), and slope angle of the inclined shaft (α) on the surrounding rock were systematically analyzed.Thereafter, the influencing laws of H, K, and α on stress, displacement, and plastic zone at the vault and haunch were explored.Results show that, when K is constant and H increases from 300 m to 500 m, the maximum shear stress, plastic zone, and radial displacement at the vault and haunch clearly increase.When H is 500 m and K increases from 0.5 to 1.5, the maximum shear stress and radius of the plastic zone at the vault significantly increase by 213.1% and 48.7%, respectively, and the radial displacement at the vault is reduced.In addition, the maximum shear stress and the radius of plastic zone at the haunch decrease slightly, radial displacement at the haunch increases substantially, and displacement at the tunnel wall changes the most.Meanwhile, α significantly affects the stress, displacement, and plastic zone at the vault, but the influence on these aspects at the haunch is minor.Lastly, the obtained results are significant for predicting the construction safety of large-slope inclined shafts and also provide a basis for the optimization design of lining structures.