Taum Sauk Upper Reservoir Rebuild

Client: Ameren Missouri | Location: Lesterville, Missouri | Year Completed: 2010

 

Taum Sauk Upper Reservoir Rebuild

 

On December 14, 2005 at approximately 5:20 AM CST the northwest corner of the Taum Sauk Pumped Storage FERC Project No. 2277 upper reservoir rim dike failed resulting in a release of the upper reservoir. Paul C. Rizzo Associates, Inc. (RIZZO) was retained to complete a detailed forensic engineering study to determine the causes of the failure. Analysis included stability and seepage, dam breach (to determine time of failure), complete review of instrument control systems, sediment transport, detailed mapping of breach zone, and drilling and sampling of remaining portions of the dike. RIZZO then analyzed and developed various options to re-build the project. Construction costs and schedule, as well as potential regulatory challenges with each option, were fully evaluated.

In order to obtain regulatory approval for the project, RIZZO conducted a complete Environmental Impact Report for both the Rebuild and the potential consequences of an engineered Overflow Release Structure which was designed to shunt a catastrophic release down Proffit Mountain to Taum Sauk Creek in a preferential direction so as to minimize human and environmental impact. The Environmental Report was subject to public meetings and significant coordination with the regulatory agencies. RIZZO also developed the required environmental permits for protection of water and control of air emissions.

RIZZO was retained by Ameren Missouri to design and prepare construction documents to re-build the upper reservoir. Various conceptual level alternatives were investigated including both repair and replacement alternatives.

Based on 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's scope of work is detailed as follows:

FORENSIC ANALYSIS: RIZZO conducted a detailed forensic engineering analysis to determine the causes of the failure. Analysis included stability and seepage, dam breach (to determine time and to evaluate mode of failure), complete review of instrument control systems, sediment transport, detailed mapping of breach zone, drilling and sampling of remaining portions of the dike, and a subsurface investigation to analyze both the existing dike and its foundation and the potential foundation of a new Dam.

DESIGN ENGINEERING: RIZZO prepared both conceptual and a detailed designs of the Rebuild, including analyzing and developing various options to rebuild the Project. Construction costs and schedule, as well as potential regulatory challenges with each option, were fully evaluated. RIZZO evaluated several alternates for a re-build and selected a symmetrical (0.6H to 1.0 V upstream and downstream) RCC dam. 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.

ENVIRONMENTAL REPORT: In order to obtain regulatory approval for the Project, RIZZO conducted a complete Environmental Impact Report for both the Rebuild and the potential consequences of an engineered Overflow Release Structure, which was designed to prevent a catastrophic release down Proffit Mountain to Taum Sauk Creek in a preferential direction so as to minimize human and environmental impact. The Environmental Report was subject to public meetings and significant coordination with the regulatory agencies. RIZZO also developed the required environmental permits for protection of water and control of air emissions.

TUNNEL LINER REPLACEMENT: The outlet works for the Taum Sauk pumped storage facility includes an 1,807 ft. long, 18.5 ft. diameter steel lined tunnel and penstock. A section of the steel lined tunnel has buckled and cracked several times during dewatering of the outlet works. RIZZO has developed a design for relining the section of the steel lined tunnel that has undergone buckling. A new 18.5 ft. diameter section with a greater thickness will be installed. The design also includes transition sections and a new drainage system to relieve external pressure. The Project also involved preparation of a bid package and assistance in evaluation of bids.

PENSTOCK INSPECTION: RIZZO performed the inspection of the outlet works for the Taum Sauk pumped storage facility and prepared the associated inspection report. The outlet works consists of a 450 ft. long, 26 ft. diameter vertical shaft, a 4,765 ft. long, 25 ft. diameter horizontal rock tunnel, and a 1,807 ft. long, 18.5 ft. diameter steel lined tunnel and penstock. Inspection activities included a scan of the vertical shaft using a video camera and Ground Penetrating Radar and a visual inspection and geologic mapping in the rock tunnel. The steel lined tunnel and penstock were visually inspected, thickness readings were taken using an Ultrasonic Thickness meter, and ovality checks were performed by a surveyor.

CONSTRUCTION MANAGEMENT: As Construction Manager (CM), RIZZO retained a full staff of on-site personnel, including: engineers, construction supervisors, AutoCAD personnel, surveyors, environmental compliance and safety personnel. RIZZO was the single point of contact for the Project and was the Owner's Representative on-site. Additional duties included coordinating and managing the work of the Contractor. RIZZO's responsibilities included: scheduling, budget and cost control, inspection of the Contractor's work, approval of Pay Applications, contract administration, preparation of contract documents and technical specifications, health and safety programs, Request for Information and approval of Project Submittals. RIZZO provided on-site supervision and coordination of all construction activities. These activities included schedule, budget and cost control, approval of submittals, responses to RFIs, Cost Estimates, preparation of Bid Documents, Contract Administration, Document Control, Construction Monitoring, Cash Flow Projections, review of Value Engineering proposals, Claim Analysis and Negotiation, Dispute Resolution, Performance Analysis, and Pay Application Approvals.

The Taum Sauk project highlights RIZZO experience with the following deliverables:

  • Structural and Dynamic Stability Analysis

  • Equipment Qualification and Testing

  • Embankment Soil Stability Analysis

  • Deformation Analysis

  • Seepage Analysis

  • Seismic Analysis

  • Stress Analysis

  • Dam Break Analysis

  • Breach Analysis

  • Potential Failure Mode Analysis

  • Comprehensive Geological and Geotechnical Investigations

  • Design Plans and Specifications for modifications

  • Instrumentation

  • Design Guides

  • Surveys

  • Drafting Services

  • Train employees in dam safety and emergency preparedness programs and activities

  • Formal, Intermediate, Emergency, and Special Dam Safety Inspections

  • Construction Oversight and Support

  • Project Management

 

 

© 2014 Paul C. Rizzo Associates Inc.
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