During feasibility and design stage, for large underground rock caverns, through an integrated investigation approach an interpretative geological model is developed with geologically critical areas predicted as geological hotspots for special interventions during construction. The initial geological model developed - which is essentially a structural model evidencing major faults, fractured zones and dykes - is updated continuously during construction of water curtain system and main cavern with focus on geological hot spots through an active design process. This active design process involves additional investigations during construction for hot spots, 3D geometrical analysis, geotechnical assessment of the cavern and verification of rock supports by detailed geotechnical back analysis using actual excavated data from water curtain and cavern heading. The geological model is improved and updated further after cavern heading and at every stage of benches for prediction of likely adverse conditions, if any, in the next benches. The predictive assessment is corroborated by observed geotechnical monitoring results; and for segments with abnormal deflections, FEM analysis is performed. The present article outlines the review and updation process of predictive structural analysis and geological models for large underground rock cavern excavations being practised in execution of one such storage project in India with an objective to reduce exposure to underground risks and ensure preparedness to address adverse scenarios.

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