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