Assessment of discontinuity related instability potential in a surge pool cavern: kinematic and distinct element approach

Safe and economical subsurface excavation requires a holistic assessment of the ground. Possibilities of stress-induced and structural failures need thorough consideration before excavation. Over-supporting an excavation is uneconomical while under-supporting can lead to disastrous results. Thus, in this research, an attempt has been made to devise the most efficient and reliable support system. An under-construction underground surge pool cavern to store and lift water at the Indian state of Telangana was taken up as the research site. The methodology involved in-depth geological and geotechnical investigations to identify possible adverse features. Rock mass rating and Q-index, were implemented for rockmass characterization. The surge pool was constructed using the Norwegian Method of Tunnelling (NMT) and validated with BIS codes. The stability analysis and support design were carried out with the help of distinct element simulation and wedge analysis for the surge pool heading portion. A right crown portion was found to be most susceptible to failure, which was also confirmed by the both the analysis. A thorough examination led to the most robust and economical support design for long-term stability.