Scope of Work
Cianbro installed a temporary debris/access platform and steel cofferdam to dewater Sections 2 and 3 of the Holtwood Dam to facilitate the demolition of the existing Bridgestone rubber dam, concrete, and embedded utilities on the crest of the spillway.
- Installed approximately 710 linear feet of steel sheet pile cofferdam fastened to the upstream face of the dam supported by a bent-plate ledger, as well as a downstream steel-supported access/debris platform with timber decking
- Performed tremie seal to sheet pile flutes and cofferdam closure walls
- Demolished/removed approximately 1000 linear feet of Bridgestone rubber dam, as well as exiting concrete and embedded items in spillway Sections 2 and 3
- Installed pier junction boxes, as well as approximately 2850 linear feet of 1 inch embedded conduit, wiring, and control cable
- Installed approximately 1800 linear feet of 4 inch embedded galvanized Victaulic air piping, including 36ea risers for the new Obermeyer air bladders
- Placed approximately 1000 cubic yards of concrete via slick line and concrete buckets, including resurfacing of a portion of the upstream crest
- Installed 700 linear feet new Obermeyer inflatable flashboard system, including 36 rubber bladder/steel gate sections, 4 embedded abutment plates, main anchor assembly, and associated restraining components
Lean, Innovative, and Unique Project Solutions
Talen Energy’s permit for construction was set to expire in December of 2015, which significantly constrained the required project completion date. However, early in the project, the addition of the upstream crest resurfacing scope, paired with difficult river conditions early in the project, prompted Talen Energy to request an accelerated schedule. Cianbro was able to compress the project duration by two months. Early coordination, collaboration, and planning between Cianbro, HDR, and Talen Energy enabled the team to develop a cofferdam design that would meet permit requirements, facilitate open access for the upstream crest work, and eliminate pile driving for risk of disturbing a submarine cable running along the face of the dam.
Cianbro procured and placed new concrete, steel reinforcement, electrical conduit, and embedded air piping over 710-feet before installing a new Obermeyer inflatable flashboard system, resulting in one of the longest Obermeyer spans ever constructed.