PREDICTING POWDER FACTOR IN MIXED-FACE CONDITION - DEVELOPMENT OF A CORRELATION-BASED ON INVESTIGATIONS IN A TUNNEL THROUGH BASALTIC FLOWS

Several approaches are available for estimating the powder factor in t unnel and bench blasting. These approaches consider those rock mass pr operties which are the most significant parameters in a rock-explosive interaction. However, they provide no information on the effects of m ixed or multiple geological formations (mixed face) on the powder fact or. Values for rock mass properties and the powder factor are collecte d along a length of 1075 m in the link tunnel of the Koyna Hydro-elect ric Project (Stage IV) in Maharashtra, India, which passes entirely th rough a mixed face and intersects more than one formation at a single location. A critical analysis of these data led to the development of a correlation for predicting the powder factor in the tunnel, consider ing uniaxial compressive strength, Barton's rock mass quality (Q), the thickness of each formation, and the effects of interformational cont act surfaces.