Cavity Encountered--Head Race Tunnel (HRT) & Resolved – A Case Study

During the excavation at Adit-4/Face-7 in the HRT, Dia 9.50 M Shape-House Shoe, we have encountered a cavity in the crown where boulders and muck were rapidly rolling down. This situation raised significant concerns regarding how to manage the issue, prompting us to consult our client, SJVN/SAPDC, for guidance on addressing this cavity in a specialized manner while adhering to technical specifications. Given the site conditions, immediately we opted for conventional supports, such as the installation of steel ribs and Shotcrete etc; however, this approach proved ineffective in containing the loose rock mass.