Elastoplastic Solution of TBM Inclined Shaft Surrounding Rocks under Non-constant Pressure with Consideration of Intermediate Principal Stress

Long-distance Tunnel Boring Machine (TBM) inclined shaft is characteristic of great changes in buried depth, large slope, and running across complicated formation. Stresses in the support and surrounding rocks after the inclined shaft excavation are obviously different from those in horizontal tunnels. Thus far, studies on stresses of inclined shafts are limited. To investigate the mechanical properties of lining-surrounding rocks in TBM inclined shaft systematically, a mechanical analysis model of TBM inclined shaft under non-constant pressure was established. The elastoplastic solution of surrounding rocks in inclined shaft was solved based on unified strength theory. Expressions of surrounding rock stresses, displacements, and the plastic zone radius with comprehensive considerations to intermediate principal stress (described by the influencing factor (b) of intermediate principal stress), lateral pressure coefficient (K0) of surrounding rocks, angle of the inclined shaft, and elasticity modulus of lining were deduced. Moreover, a computational analysis based on an engineering case was performed. Results demonstrate that, surrounding rocks are more stable if the intermediate principal stress makes greater contributions. The value of b increases from 0 to 1, whereas the plastic zone radius of surrounding rocks and the radial displacement of tunnel wall decrease by 9.96% and 18%, respectively. The K0 considerably affects the radius and displacement of the plastic zone on surrounding rocks along different directions. When b=1 and K0 increases from 0.8 to 1.2, the horizontal displacement of the tunnel wall increases by 40%. A larger angle of the inclined shaft has more significant influences on the radius and displacement of the plastic zone. With the increase in the elasticity modulus of lining, the radius and radial displacement of the plastic zone decrease accordingly. The proposed model provides important theoretical references to safety analysis and support scheme selection for surrounding rocks in similar TBM inclined shaft projects. © 2023 School of Science, IHU. All Rights Reserved.