First piece of equipment goes in at the Red Rock Hydroelectric Project
Dec 29, 2016
For almost a year and a half, construction work at the Red Rock Hydroelectric Project (RRHP) consisted of “deconstruction” or site preparation work. Temporary coffer dams and a dike were installed to allow work on dry ground, concrete retaining walls were poured, and more than 200,000 cubic yards of dirt and bedrock were excavated; all to prepare for the construction of a power house and water intake structure.
In early 2016, the foundations of the power house on the downstream side of the dam finally began to take shape. Throughout the year, construction crews have been installing rebar, which is assembled on the site, for strength and reinforcement of the power house structure. Then concrete is poured in “lifts” or sections, some of which contain more than 1,000 cubic yards, or 100 truckloads of concrete. As of November 30, more than 1,360 tons of rebar and 22,880 cubic yards of concrete had been installed for the power house.
These concrete pours are complicated and intricate. Each lift is precisely engineered to incorporate the elements of the power house that will be contained in that section of concrete. Wooden forms or “block-outs” are set in place to create voids in the concrete where equipment, passageways, piping, valves, and electrical components will reside when the power house is completed. As an example of the precision needed in these concrete pours, the circular steel frame around the turbine blades must be only 1/16 of an inch from the blades.
On December 1, a milestone was achieved as the first piece of turbine equipment, the steel draft tube liner for Unit 1, was set inside the power house at the RRHP. The steel liner for Unit 1 was prefabricated in York, Penn., and shipped to the site in two halves, which were welded together at the site. The steel draft tube liner will direct water from the turbine to the concrete draft tube and back to the Des Moines River. RRHP will include two units, and the draft tube liner for Unit 2 was set on December 16.
Preparation for equipment placement will start from the bottom. That means equipment that will be near the end of the process of producing hydroelectricity will be installed first. Once the power plant is operating, the flow of water from the Des Moines River will enter the intake structure on the upstream side of the dam, flow through penstocks (large steel tubes) through perforations in the dam, into a spiral case, through the turbine, out through draft tubes, into the tailrace, and finally back into the river.
The next element in the construction process is building the concrete portion of the draft tubes. Following placement of structural concrete for the power house foundation, custom made wooden forms, which resemble large wooden shoes, were shipped to the site in sections and assembled in place. Once the wooden forms were fully assembled and embedments such as rebar and electrical conduits were installed, concrete was placed around the forms in lifts. Once the concrete has been poured and reached its engineered strength, wooden forms are removed and the steel draft tube liner is set in place. When completed, the draft tube liner must be perfectly round and it must be set within 4/1000ths of an inch of being level -- that is approximately the thickness of two sheets of paper. Next, the draft tube liner is secured with turn-buckles to lock it in place and then buried in concrete to further solidify the installation.
Once the draft tube liners are concreted into place, workers will continue to make their way up toward the turbine and generator installation, spiral case and penstock completion, and the intake structure on the upstream side of the dam. Completion of work on the entire project is anticipated in late 2018.