Geotechnical Challenges and Solutions in the Construction of Underground Powerhouse with Shallow Basalt Rock Cover: A Review of Sardar Sarovar Narmada Project Case Study

Abstract

The Sardar Sarovar Narmada Project in Gujarat, India, provides a critical case study of underground powerhouse construction, completed in 2003, under challenging geological conditions, specifically with a shallow basalt rock cover. This paper begins by detailing the assessment of the geotechnical challenges encountered during the excavation of a 58-meter-high powerhouse chamber, including the evaluation of rock mass properties and in-situ stress using flat jack and hydro-fracture tests. These assessments identified significant stress redistribution and distress in the rock mass, leading to cracks aligned parallel to the cavern’s longer axis, which impacted critical structures such as pressure shafts and bus galleries. To address these challenges, a comprehensive engineering geological analysis was conducted, employing modern instruments like DEMAC gauges to monitor shear zones and crack development. Advanced analytical methods, including the 3-D Finite Element Method (FEM) and the 3-D Distinct Element Code (DEC), were utilized to assess the cavern's behavior under the identified stresses. This study underscores the critical importance of detailed geotechnical analysis and the careful selection of support systems for ensuring the stability of excavations in challenging environments like shallow basalt cover. The findings highlight the value of adaptive support systems and comprehensive geotechnical assessments in managing stress relief and deformation in similar geological conditions. Although the results are based on the specific case of the Sardar Sarovar Narmada Project, they provide valuable insights for the design and construction of underground powerhouses in jointed rock masses with shallow cover. These insights contribute to the broader geotechnical literature by offering practical guidance for similar underground construction projects. Future research should apply these lessons across a range of geological settings and rock types, refining and generalizing design practices to enhance construction strategies for underground caverns in various geotechnical contexts.