The Holtwood Hydroelectric Plant has been generating electricity since 1910, using the power of the water held back by a 55-foot-high dam across the Susquehanna River. But after more than 100 years, the plant needed a major, $438 million upgrade to continue to meet the region’s demand for power. When finished, the project added 125-megawatts to the facility’s existing 109-megawatts of generating capacity.
Froehling & Robertson, Inc.’s main role on the project was inspection of state-of-the-art concrete formwork, and the verification, measurement, and inspection of embedded concrete items including: reinforcing steel, rebar couplers, electrical conduits, embedded precast panel anchor plates, embedded structural steel anchor bolts, embedded mezzanine anchor welding plates, water pipelines, air pipelines, weep holes, various forms of waterstop, and electrical grounding cables.
Each individual pour location carried with it unique concrete placement challenges. In some cases, design modifications had to be made because practical placement of the pour was impossible to achieve as shown in the drawings with all of the embedded items occupying the same space. F&R frequently assisted and offered modification suggestions, allowing construction to proceed in a time-effective manner while ensuring work was done correctly. Measurements such as the circularity, geometric and magnetic center, axial height, and radial verticality of turbine parts, also had to be monitored and verified daily.
F&R’s inspections took place over years, some within the machine, crawling between parts and accessing difficult to reach areas. F&R inspectors often had to be accurate to a thousandth of an inch, with some individual measurements and verifications taking days to complete.