ETT/CREZ Direct Embedded Pole Foundation Load Tests

The Electric Transmission Texas/Competitive Renewable Energy Zone (ETT/CREZ) project consists of seven 345kV transmission line segments with a total length of over 400 miles. The project is located in North Central Texas. The transmission line consists of tubular steel poles supported by two types of foundations. The poles will be either direct embedded with a concrete backfill for the more lightly loaded tangent pole structures; or drilled shafts with full length anchor bolts for the more heavily loaded tangent, running angle and dead end structures. Over 2,400 or about 90% of the total number of structures will be direct embedded with concrete backfill. In the past, AEP Foundation Design Engineers, as well as most of the utility industry, traditionally assumed that a direct embedded pole behaves the same as a reinforced concrete drilled pier, however no full-scale foundation load tests have ever been performed to confirm this assumption. Due to the large number of direct embedded foundations to be installed, a tremendous opportunity for construction savings existed, even if only one foot of embedment were saved on average for each installation. To seize this opportunity, the engineering team decided to conduct two fullscale direct embedded pole tests. The primary goal was to reduce foundation construction costs, while maintaining reliability. This was accomplished by performing preliminary direct embedment depth calculations using MFAD and test site-specific soil data, installing the test poles to the calculated embedment depths, and subsequently conducting the load testing. The resulting field-measured load displacement responses were then analyzed and compared with the original design assumptions and methodology. Adjustments were made to the design approach as appropriate, and used in the final designs for all direct embedded foundations. As a result of the testing program, the engineering team was able to realize a reduction in embedment depths ranging from one to four feet, which will have a beneficial impact on foundations costs. Furthermore, the knowledge obtained from the tests allowed the team to confirm the design approach and thus improve the reliability of future, direct embedded pole designs.