This technical paper presents an in-depth exploration through advanced 3D numerical studies focused on the excavation and support systems for the Powerhouse and Transformer Hall Caverns in the challenging geological terrain of Himachal Pradesh. The preliminary design phase involved meticulous 2D modeling in PLAXIS software, establishing a fundamental understanding of ground behavior. Subsequently, the study progressed into a detailed 3D design phase using MIDAS GTS NX software, enabling a comprehensive analysis of rock mass behavior. A key highlight of this research is the incorporation of a sensitivity analysis on input parameters, providing valuable insights into the robustness and reliability of the numerical model. This analysis enhances our understanding of how variations in input parameters influence the outcomes of the excavation and support system, offering a nuanced perspective crucial for real-world applications. Furthermore, all interconnecting tunnels with the powerhouse and transformer hall were intricately modeled in 3D, capturing complex interactions within the entire underground network. Construction-staged analysis was conducted to simulate the evolving conditions during the construction process, allowing for a comprehensive assessment of the excavation and support systems’ performance over time. This study provides a methodical approach to model the entire 3D powerhouse area with emphasis on modeling the disturbed rock mass zone due to blasting and guidance in selection of suitable design parameters conservative enough to cover the limited no. of field measurements and uncertainties. The omission of specific project names ensures confidentiality, while the presented methodology remains universally applicable to similar projects, marking a substantial leap forward in advancing best practices for underground infrastructure development.