Blasting and Excavation in Sensitive Rock

ABSTRACT: There is a fairly common belief that any rock excavation task can be accomplished with explosives if standard cautious blasting formulas are used appropriately, especially when accompanied by vibration limits Unfortunately, that conclusion is often not true. In some cases, that approach will not give satisfactory results, and vibration restrictions may serve no purpose but to shut down the job. At times, the sequence of the work is at least as important as the blast designs. Sometimes, success may depend on the method of excavation. And in some cases, the rock excavation task could not be accomplished by any means whatever, without some extra mechanical stabilization. Successful work in sensitive rock requires a careful study of the geological and physical characteristics of the site and a determination of the potential failure mechanisms involved. This paper describes several case histories to illustrate some of these important issues.