Abstract: This paper studies the joint effect of seepage force and axial stress on the stress and displacement of circular tunnel. The circular tunnel is simplified as an axisymmetric model and the seepage field is simplified as volumetric force in the stress field. The excavation cross-section of surrounding rock is assumed as a plane as well, and an axial stress perpendicular to the plane is further introduced. Nonlinear solutions for the stress and displacement of circular tunnel are deduced considering the joint effect of axial stress and seepage force, based on the generalized Hoek-Brown failure criterion and the non-associated flow rule in elastic-brittle-plastic rock mass. Numerical simulations are also employed to analyze the distribution of stress field and displacement field in plastic zone of a circular tunnel under the joint effect of axial stress and seepage force. The calculated results show that the displacement in plastic zone increases significantly with the gradient increment of the seepage pressure, compared with the situation without seepage force. The radius and stress of surrounding rock in plastic zone increase when axial stress is the intermediate principal stress, while the radius and stress have less change when axial stress is the major or minor principal stress. It can be concluded that the seepage force has negative effects on the stability of circular tunnel, and the axial stress significantly influences the stress and displacement of the circular tunnel, especially in water-rich areas. Therefore, it is necessary to consider the joint effects of axial stress and seepage force to ensure the stability of circular tunnel in water-rich area.

Key words: elastic-brittle-plastic model, axial stress, seepage force, Hoek-Brown failure criterion, circular tunnel