CIM Vancouver 2002
Jody K. Todd,
Abstract Double benching has been utilized as an excavation technique in open pit mines for many years. This process involves drilling, blasting, and excavating the material for the design bench height. A second bench is then excavated without the creation of a catch bench, i.e. only minimal offset from the first bench face is allowed when drilling off the second bench. The result is a double high bench face or double bench.

The offset of the drill from the bench face, when drilling off the second bench, projects the lower bench face into the pit somewhat. This reduces the maximum attainable bench angle and enhances the probability of rock escaping the catch bench. The generally utilized process of trim blasting also can impact on the final bench profile by contributing to blast damage of the face.

BHP Diamonds, Ekati Mine, has pioneered the usage of a technique that eliminates this offset. Double benching is conducted by drilling off a single, 30m pre-shear (two 15m benches) to define and protect the final bench profile.

This article provides a comparison of the attained face angles obtained in the field utilizing both of the above methods, as well as a comparison with the analytically predicted angles prior to excavation.
Keywords: bench design, pre-shear, double bench, statistical bench design, rock fabric, face control, drill offset, large hole pre-shear, bench scaling, catch bench reliability
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