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 sigma(a0) is more significant when strain softening is considered, compared with the results of a perfectly elastoplastic model. When the axial stress sigma(a) is sigma(1) or sigma(3) at the initial yield, an increase or decrease in sigma(a0) intensifies the deformation and failure of the surrounding rock. When sigma(a) is sigma(2) at the initial yield, 3D plastic flow partly controlled by sigma(a) may occur, and an increase in sigma(a0) intensifies the deformation and failure of the surrounding rock. The effect of sigma(a0) will be amplified by considering dilatancy. Considering both strain softening and dilatancy, when sigma(a0) is close to the tangential in-situ stress sigma(t0) or significantly greater than sigma(t0) (1.5 times), sigma(a) will be sigma(2) or sigma(1) at the initial yield, and then 3D plastic flow will occur. In the deformation prediction and support design of a deep tunnel, sigma(a0) should not be ignored, and the strain softening and dilatancy behavior of the surrounding rock should be accurately considered.