Drilling (continued)

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6. Carefully select the points at which holes will be placed. Use natural points of weakness, and keep in mind your total breaking needs for the project. Evaluate the site and proceed accordingly. If you plan to remove a rock entirely, position the holes as perpendicular as possible to the largest face parallel to its strata (see A below). If the rock is to remain in place with only parts removed, a different technique is used (see B below).

A. Drilled holes are perpendicular to the surface being worked. If wedge and feathers are used in this instance they will be less likely to be unduly stressed, because the compression forces of the rock are more evenly distributed on them. This rock will probably be split into chunks that will allow its complete removal. Arrows indicate probable direction of splitting.

B. The drilled hole is not perpendicular to the surface being worked. Splitting will be both less predictable and less efficient in this situation. Be aware also that when you work the wedge into the hole it will be more prone to bending or breaking because the compression forces are distributed unevenly. You have already determined that only a section of the rock will be removed. That is what you can expect to happen here. Arrows indicate probable direction of splitting.

The same principles can be applied if a prospective trail tread crosses a rock face.

A. If the rock looks and feels solid, drill to remove it completely.

B. If the rock is weathered, seamy, or soft, perhaps you can chip it flat.