Abstract:
Standard practice for CHANCE® helical anchors is to use center-to-center spacing five times the diameter of the largest helix plate. For helical anchors with closer spacing, conventional wisdom recommends the anchor allowable load be reduced due to group effects. The magnitude and extent of the capacity reduction is left to the design professional to determine. This study investigates whether or not a group effect reduction in capacity is justified for single-helix anchors loaded in tension. Load tests from several sites with a variety of soil conditions were conducted. Anchors with identical 10†helix plate diameter were installed side-by-side and pull tested simultaneously. The spacing between the anchors varied from 5D down to 1D, where “D†is the diameter of the helix plate. The results are discussed in the conclusion and are used to justify how close single-helix anchors can be spaced without any group reduction effect.