Hard Rock Drilling

Drilling high quality granites and other igneous rocks with strengths in the range of 20,000 to 60,000 psi cannot be done with conventional tools. For this Tri-State uses a pneumatic Cluster Drill from Ingersol Rand. The picture opposite shows the water cascading out of the casing. The cluster Drill is driven by air powered by 3-1300 cfm compressors linked to the hammer.

This Cluster Drill which cuts a 48 inch diameter hole has 4 perimeter hammers and 3 interior hammers strategically placed in the shell. They work together spalling off chunks of rock as the drilling machine rotates the tool slowly in the hole. Production rates of 1 to 2 feet per hour were recorded for this bridge job in Wausau for the Wisconsin DOT.

Bridge piers must be drilled exactly where they are designed to go. Sometimes the river bottom doesn't cooperate. This was the case with two of the piers on the Wisconsin River in Wausau. The rock surface sloped sharply downward across the 4-foot area where the hole was intended to go. this prevented the hammers from hitting it directly and caused the tool to slide.