Lateral Resistance of Helical Pile Groups-Case Study

Helical piles are used frequently in western Canada to support transmission line towers due to their high tensile capacities and their ease of installation in difficult soil conditions such as soft clays or organic materials. There are several studies documenting their performance under lateral loads. However, most of the available studies are for single piles. The use of group of piles to support the foundations of transmission line towers is very common. Depending on the type of tower (i. e., tangent, light angle, heavy angle, or dead end) and loading conditions, groups of two to five piles are frequently used. In the present study, two pile groups, each of them with two piles, were presented. The paper documents the pile configuration and installation details of pile groups. The pile groups were installed into very stiff clay till so that one pile was vertical and the trailing pile was inclined at batter angle of either 20 or 30 degrees. Soil stratifications and groundwater conditions were also summarized. Lateral load tests were performed using ASTM standard ASTM D3966 (ASTM 2013) for lateral load tests and the results were summarized in the paper. The results of the load tests were compared to a theoretical model using nonlinear p-y curves for lateral loading and t-z curves for axial loading. Based on the results of this study, it was found that a group of two helical piles can develop considerable resistance to lateral loads and that the lateral resistances of the pile group are highly dependent on the batter angle.