Wedge analysis of underground powerhouse

Failures of underground excavations are uncommon, but all underground excavations undergo localized overbreak as the desired dimensions of the opening readjust themselves to geological realities. Surface excavations are less stable than underground openings and experience failures more frequently. The sensitivity analyses of underground powerhouse caverns of widths 27.5 m and 23.0 m of a multipurpose project in the Himalayan region have been done using the commercially available software UNWEDGE which is designed to be quick, interactive and simple to use analysis tool for the design and stability of underground wedges defined by intersecting structural discontinuities in the rock mass surrounding an underground excavation. There are six joint sets which have been divided into two sets of three joints for analysis. The joints have been analysed with and without water pressure. The worst case of failure of wedge has been found out by varying joint sets and trend of excavation. In this paper, the methodology, details of software & analysis, results and important conclusions arrived at are presented.