Project Location: Holly Street Power Plant & Pleasant Valley Rd, Austin, Texas
Client: Client: Duke Engineering & Services - Austin Energy, Austin, Texas
Dates: January 2002 to May 2002

Two transmission towers for 138-kV lines help to deliver energy from the Holly Street Power Plant accross Town Lake in the City of Austin. These towers were evaluated for an increased number of transmission lines thus requiring a review of their structural integrity and foundation response.

These towers were built in the late 1950's and their foundation consisted of large concrete caps on top of irregular combinations of straight and raked steel piles made of H sections. The penetration of those piles was not clear from the original plans and a site investigation with non-destructive sonic methods was performed by LCR&A. The tests were based on the use of sonic waves to investigate the length of the existing piles under the concrete caps. Dynamic loads were generated with small blows of hammer impacts on the pile cap and electronic transducers of high sensitivities recorded the signals. Pile lengths were computed based on traveling time and speed of compressive waves on each test pile. Capacities of the existing foundations were evaluated using 3D models of the cap and piles and using non-linear soil properties. Two designs were made for strengthening alternatives, one based on screw anchors and one solution based on drilled shafts.