7 Steps to Install Expanding Rock Anchors
Written by Tim Staelens on February 13, 2019
7 key steps to install expanding rock anchors.
- Choose anchor site carefully. Rock anchors will only perform effectively in solid competent rock (Class 0 Soil).
- Drill the hole into the competent rock a minimum depth of
12 inches along the drill steel. 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 an 1/8th inch larger than the diameter of the unexpanded anchor. For example, the hole drilled for a R315 is 1-7/8 inch 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 dia. 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 facilitate the wedge expansion.
- Rock anchors set in holes drilled 12 inches deep in competent Class 0 Soil (hard rock) will develop the full strength of the anchor rod. This can be either 3/4 inch rod - Minimum Ultimate Strength of 23,000 lbs. - or 1 inch rod - Minimum Ultimate Strength of 36,000 lbs.
- It is good practice to grout the rock anchor after it is installed as 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), .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 strand(s) may be attached to the anchor eye and fully loaded. The optional grouting may be done before or after the guy strands are attached.
