Abstract A large underground hydroelectric power project (6 x 250 MW) is under construction on the left bank of Satluj River in Himachal Pradesh by Nathpa Jhakri Power Corporation. As a part of this project, four large (525 m long, 16 m wide, 27 m high) underground desilting chambers are being excavated by drilling and blasting. This paper describes the sequence of excavation of the desilting chambers, the geotechnical conditions, blast designs for central top heading, side slashings and horizontal benching. The performance of blast designs is evaluated in terms of pull, overbreak and powder factor and the results achieved are presented. Based on the data generated, the applicability of Rock Mass Quality (Barton et al. 1974) for blasting at various stages of the excavation of the chambers is discussed.
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