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Based on our substantial investigation and design, RIZZO determined that a repair of the existing Dike was not technically feasible due to flaws in the original construction. Substantial areas of the existing dike were founded on residual soil. Additionally, few construction controls were utilized to control the gradation and character of the rock fill. Due to this and other factors, a complete re-build of the upper reservoir was required.
RIZZO evaluated several alternates for a re-build and selected a symmetrical (0.6H to 1.0 V upstream and downstream) roller compacted concrete (RCC) dam. The symmetrical slopes reduce the demand on the rock foundation and allow for inclusion of less than ideal aggregate to create the RCC mix. This allowed the use of recycled aggregate for the RCC. The existing rockfill dike material (rhyolite) will be processed and utilized to create aggregate for the RCC.
Fly ash was a primary cementious component of the RCC Mix, which contained 100 pounds of both cement and fly ash per cubic yard. RIZZO successfully investigated the use of a landfilled fly ash. The fly ash was excavated from an existing AmerenUE facility, processed, and utilized in the RCC Mix. In addition to cost savings by not having to purchase commercial fly ash, this created additional landfill space for use by Ameren. Additionally, the use of fly ash reduced the heat of hydration of the overall RCC Mix.
RIZZO developed an appropriate seismic design basis for the site and completed a series of finite element analyses to predict seismic stresses during a design basis earthquake event. All calculations, design reports and construction documents were reviewed by the Federal Energy Regulatory Commission (FERC) and an Independent Board of Consultants (BOC). RIZZO formally presented various design alternatives to both the FERC and the BOC for review and approval.
During the life of the project, the following tasks have been completed with regard to reconstruction of the Upper Reservoir.
Develop conceptual level repair alternatives including technical, cost and schedule;
Completion of subsurface investigation to analyze both the existing dike and its foundation and the potential foundation of a new Dam;
Develop design basis for complete re-build of the upper reservoir;
Develop Construction Drawings and specifications for re-build;
Site Specific Mix Design Program for RCC;
Evaluate use of landfilled fly ash including processing;
Develop formal Environmental Report and support Ameren with environmental permitting;
Design of Instrumentation and control system for dam safety and plant operation; and
Construction Management and Resident Engineering during Safety Stabilization and Rebuild of Upper Reservoir Dam.
The design and construction of the new Taum Sauk Upper Reservoir Dam is in compliance with United States Federal Regulations as implemented and monitored by the United States Federal Energy Regulatory Commission (FERC) and by the State of Missouri Department of Dam Safety. The design and construction was reviewed by the Owners Department of Dam Safety, the staff at the FERC Headquarters as well as FERC regional offices in Chicago and Atlanta. In addition, the design and construction was reviewed and approved by an Independent Panel of Outside Consultants (IPOC) retainded by FERC and a Independent Board of Consultants retained by the owner for the design and throughout the construction and startup.
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IWPD&C Magazine 1/2009 Article on Taum Sauk Rebuild
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