Boulders and Rock Drill Patterns

Aiming cracks:
Drill sets of two or three holes on a close spacing of 1 ft or less c/c. Aim the lines of these holes to create smaller pieces. Keep the holes no closer than 2-3 feet from the edges of the boulder. Drill about ⅔^rds of the height, unless the boulder is imbedded in the ground. If breaking the entire boulder drill through, and then back off about 1 ft on rest of holes. If you are sheering the boulder off it may be best to drill angled holes under the boulder to sheer it to an elevation.

This type pattern may break a boulder into a lot of pieces, a lot depends on the type of rock. It is is like Granite that has a grain, it may be hard to break across the grain and this pattern may only get long pieces. It is hard to predict on a boulder how it will break. However, if the burden is a good bit in from the face the rock may stress in more direction that one and cracks may go in more than one direction out of a hole.

Smaller Boulder breaking up in to smaller pieces. Many times in this instance the best hole is the smallest diameter that can be drilled. Drill about 2/3rds of depth.

Drill angled holes under and sheer off below desired grade, if desired then add vertical holes to break down more.



Note example drilling with a jack leg.

This rock may need the toe drilled to get the face started, the grid on top would be staggered if possible at 8 to 15 times hole diameter depending on type of rock. Drill at least 1 ft below desired grade.