First and foremost, when installing expanding rock anchors for foundations, it’s important to choose your anchor site carefully.
Being mindful of expanding rock anchors for foundations
- Rock anchors will only perform effectively in solid competent rock (class 0 soil).
- Drill the hole into the competent rock a minimum depth of 1 foot. Be sure to drill so that the anchor rod will be in line with the guy.
- Holes should be drilled so the diameter is optimally 1/8 inch larger than the diameter of the unexpanded anchor. (For example, the hole drilled for a R315 is 1-7/8 inches in diameter. However, drill bits are usually available in 1/4-inch increments. In practice, a 2-inch diameter hole is drilled for the R3 series anchors and a 2-1/2-inch diameter hole is drilled for the R1 series anchors.) Be sure to thoroughly clean the drilled hole of rock dust and debris.
- Slide the anchor down in the hole. Use a bar through the eye to turn the rod until the anchor is fully expanded against the sides of the hole. Removing the wedge tie will occasionally help facilitate wedge expansion.
- Rock anchors set in holes that are drilled 1-foot deep in competent class 0 soil (hard rock) will develop the full strength of the anchor rod. This can be either a 3/4-inch rod (a minimum ultimate strength of 23,000 pounds) or a 1-inch rod (a minimum ultimate strength of 36,000 pounds).
- It’s good practice to grout the rock anchor after it’s installed. This is an added measure to help protect the rock from degrading. Grouting may be performed using a funnel and PVC grout tube, which extends down the hole to the top of the wedges. A flowable, neat cement grout (no aggregate) with a .4 to .45 water-to-cement ratio is suitable for grouting rock anchors. The grout will cover the drilled rock and prevent it from weathering over time.
- The guy strands can then be attached to the anchor eye and fully loaded. The optional grouting may be done before or after the guy strands are attached.