Download PDF version (403.5k) Log In or Register to view the full article as a PDF document.

Threaded Dowels

With the outside form completed, the next step was to drill holes for the dowels that would anchor the foundation to the ledge (Figure 3, page 24).

ledge3a-2.jpg (9021 bytes)

ledge3b-2.jpg (7961 bytes)

ledge3c-2.jpg (8299 bytes)

ledge3d-2.jpg (7809 bytes)

Figure 3. The author’s crew used a Bosch rotary hammer to drill over 300 holes in the rock outcroppings (top left). After blowing the dust out of a hole (top right), they injected epoxy (bottom left). To ensure good coverage, they also coated the rod and worked it up and down in the hole (bottom right). Our engineer specified 3/4x12-inch-diameter dowels set 7 inches deep in 7/8-inch-diameter holes. Although we could have used 3/4-inch rebar for the dowels, we chose 3/4-inch galvanized threaded rod instead, because the epoxy used to anchor the dowels would bond better to the sharp thread profile (we were careful to use rod that was free from any oil coatings). At a spacing of 2 feet on-center, we needed 132 dowels. Considering all the dowel and form stake holes to be drilled, we needed the right tool. As a rock climber, I know firsthand how long it takes to drill dependable rock anchors, so I decided to use a 11/2-inch Bosch SDS rotary hammer (S-B Power Tools, 4300 W. Peterson Ave., Chicago, IL 60646; 773/286-7330). It took approximately 90 seconds to drill each 7-inch-deep hole. The drill bit lasted for about 22 holes, but it could be retooled instead of discarded.