Helical Anchor Piles Under Lateral Loading

Anchors are used in civil engineering practice to provide resistance against uplift and overturning forces for structures such as transmission line towers, aircraft mooring, pipelines, offshore structures, mobile homes, and so forth. Although there are a wide variety of anchor types available, helical screw anchors, consisting of a steel shaft to which one or more helices are attached by welding, are finding wider usage particularly for the support of transmission line towers. Because these anchors are installed by truck mounted power augurs they can be used immediately after installation.

Although there exists in the geotechnical engineering literature a variety of techniques for evaluating lateral-load capacity of piles, there are no published methods for analyzing helical anchor lateral stability when used as piling. The present study was undertaken to develop suitable mathematical models based upon the current state of the art for determination of lateral-load capacity of helical-type anchor piles. The model selected was patterned after Matlock and Reese's elastic theory model. The model was modified to take into account the influence of the method of installation and other unique characteristics of this type of foundation. Based on the results of this study it was found that helical anchor piles can develop significant resistance to lateral loads, and this resistance is almost exclusively controlled by the extension shaft diameter.