Effect of Axial In-Situ Stress in Deep Tunnel Analysis Considering Strain Softening and Dilatancy

In many previous tunnel analyses, the axial in-situ stress was ignored. In this work, its effect on the deformation and failure of the surrounding rock of a deep tunnel was revealed, considering the objective strain softening and dilatancy behavior of the surrounding rock. Analysis based on the incremental plastic flow theory was conducted, and C++ was used to write a constitutive model for numerical simulation to verify and further analyze this effect. Then, the results were validated by the field monitoring data of a coal mine gateway. Results show that the effect of the axial in-situ stress σ a0 is more significant when strain softening is considered, compared with the results of a perfectly elastoplastic model. When the axial stress σ a is σ 1 or σ 3 at the initial yield, an increase or decrease in σ a0 intensifies the deformation and failure of the surrounding rock. When σ a is σ 2 at the initial yield, 3D plastic flow partly controlled by σ a may occur, and an increase in σ a0 intensifies the deformation and failure of the surrounding rock. The effect of σ a0 will be amplified by considering dilatancy. Considering both strain softening and dilatancy, when σ a0 is close to the tangential in-situ stress σ t0 or significantly greater than σ t0 (1.5 times), σ a will be σ 2 or σ 1 at the initial yield, and then 3D plastic flow will occur. In the deformation prediction and support design of a deep tunnel, σ a0 should not be ignored, and the strain softening and dilatancy behavior of the surrounding rock should be accurately considered.