Abstract: Unfavorable geological structures and weak strata play a decisive role in regulating the stability of surrounding rock in underground caverns at the Kala hydropower station. In light of this, a 3D fine jointed rock mass model with different levels of discontinuities and weak strata is constructed by using the discrete element method. Utilizing this jointed rock mass model, the stability of the underground caverns and optimal spacing between the main powerhouses and the main transformer room are analyzed. The numerical findings indicate favorable overall stability of the underground caverns, affirming their feasibility for construction. However, some engineering geologic concerns emerge, including significant deformation of the surrounding rock mass in the T₃z^2-5 weak stratum zone and block sliding triggered by joint cutting. Addressing these issues necessitates tailored support treatments. The spacing between the main powerhouses and the main transformer room is optimized via a qualitative and quantitative assessment accounting for variations in the surrounding rock field following cavern excavation as well as economic and mechanical indicators. The optimum spacing between the main and auxiliary powerhouses and the main transformer room is determined as 50 meters. Comprehensive analysis enables the identification of an optimized spacing that enhances economic efficiency and operational performance. The research findings carry substantial implications for both the optimization of cavern design and the safe construction of Kala hydropower station.

Key words: underground caverns, stability of surrounding rock, discontinuities, 3DEC, optimization of cavern spacing, Kala hydropower station