Abstract: The axis direction of underground water-sealed cavern plays a pivotal role in surrounding rock stability, support costs, and construction safety. We present a comprehensive optimization method together with evaluation indexes for the axis direction of cavern in line with engineering characteristics of underground water-sealed cavern. Firstly, we determined the optional range of axis direction according to specifications in China. Subsequently, we determined the optimal axis direction in equivalent continuum model and in discontinuous medium model, respectively, with evaluation indicators including the maximum displacement of surrounding rock, the volume of plastic zone, the stability coefficient, and the maximum shear displacement on joint surface. Afterwards, we determined the optimal axis direction of cavern with support pressure as evaluation index based on key block theory. Finally, we obtained the optimal axis direction comprehensively through holistic analysis of the calculation result of each index. Research findings suggest that the numerical model should include the excavation face to reflect the safety of construction process. In the determination of stability coefficient of surrounding rock based on strength reduction method, we should select the abrupt change point on the displacement-reduction factor curve as the critical stability coefficient rather than by calculating misconvergence. The present method has been proved to be feasible and reliable in application to an underground water-sealed cavern project in Shandong Province.

Key words: underground water-sealed storage cavern, axis direction of cavern, optimization method, discrete element simulation, key block theory