Full Scale Direct Embed Steel Pole Load Test

Historically, direct embed H-frame foundations were installed using the "rule of thumb" 10 percent plus 2 feet. This rule does not address changes in soil conditions, backfill type, or different loading conditions. The embedded portion of the pole behaves similarly to a drilled concrete foundation because the backfill material resists lateral and axial forces and overturning moments. Due to the presence of a backfill material and surrounding soil, multiple failure modes may exist for a direct embed foundation. The interaction between the pole and the backfill, and the interaction between the backfill and the surrounding soil may not be easily predicted and can vary depending on the line location and contractor installation. Little consideration has been given to accurately predict the foundation capacity of direct embed structures. Prior to our research, several projects were planned on the Ameren Transmission system using tubular steel H-frame structure with direct embed foundations. Full scale load tests were conducted to determine an effective direct embed foundation design. Multiple structure heights and configurations were tested, and the results were compared to common structural and foundation software. The results showed that the combination of quality backfill material, proper backfill installation, and proper structure bracing can reduce structure overturning and improve foundation resistance. These results also provided a cost-effective design for all future projects using direct embed structures.