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In Korea, the underground silo structure for low- and intermediate-level radioactive waste disposal facilities has been constructed and operated since 2014. Large-scale earthquakes occurred in 2016 and 2017, respectively, in Gyeongju and Pohang areas near the underground silo structures, and interest in the stability of the underground silo increased significantly. In this paper, one-dimensional free-field analyses have been carried out before the three-dimensional silo dynamic analyses subjected to earthquake loadings. As an additional study, a new form of the finite element equilibrium equation is derived in terms of relative motions, which is essentially the same equation expressed in terms of total motions where the base shear force is applied to the earthquake load. The accuracy of conventional finite element solutions is evaluated by directly comparing them with closed-form solutions by frequency domain analysis such as SHAKE91.

The underground silo was constructed as a facility for the disposal of low- and intermediate-level radioactive waste. It is divided into three parts: the upper-dome core, the lower-dome core, and the cylindrical-space core. Numerical parametric studies on the stress distribution occurring in the surrounding rocks around the underground silo are presented in this paper. It is assumed that the soil layer was distributed to a depth of −4.3 m from the ground level, the weathered rocks were distributed to a depth of −9.5 m from the bottom of the soil layer, and the rocks were distributed in the lower part of the weathered rocks. A 2D axial symmetric finite element model was considered for the numerical analysis of the underground silo. A 3D finite element model was used to verify the reliability of the 2D axial symmetric model. Finite element analysis was carried out under various ratios of in situ horizontal stress to vertical stress (Ko). The numerical results obtained through these analyses include detailed stress states in the p–q and octahedral planes at key locations of finite element models around an underground silo. Contours of safety factor distributions are also presented to evaluate the overall structural safety of the surrounding rock mass, which is the main supporting body of the underground silo.