Grand Falls Dam and Spillway Rehabilitation
Constructible dam design enhancing safety and reducing environmental impacts
Pennecon Heavy Construction (client), Nalcor (owner)
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Grand Falls, Newfoundland, Canada
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2017 - 2019
Recipient of Award of Excellence at the 2020 Canadian Consulting Engineering Awards.
Zero lost-time safety incidents.
Project completed a year ahead of the original construction schedule.
Challenges
- Grand Falls Dam's design concept presented serious constructability and safety issues. Faced with a narrow window of time prior to the commencement of the construction season, a constructible alternative was required.
- The bedrock foundation, as exposed, was found to be composed of high-quality granitic rock but it was highly irregular.
- Seepage through the dam was much greater than expected, with exceptionally high concentrated flows occurring through eroded construction and lift joins that threatened effective concrete placement.
Solutions
- Provided EPC services including design engineering, construction supervision, and on-site quality control.
- Application of advanced hydrotechnical principles demonstrating that the 10 inflatable gates originally thought to be required were replaced with a simple overflow weir constructed immediately downstream of the existing spillway.
- The original cofferdam concept was replaced by a first-of-its-kind “flash board” cofferdam solution that further reduced costs, enhanced constructability and safety, and eliminated environmental concerns associated with the original solution.
- Advanced CFD analyses were performed to verify the ogee weir capacity, the suitability of the solution to the fishery, and to develop step heights tailored to better suit the contractor’s preference for formwork, reducing costs, and enhancing schedule.
- Installation of a “plumbing” system within the body of the dam to collect seepage water at the source, control it during the concrete placement activities, and discharge the seepage flow at the toe of the dam.
Highlights
- New dam design eliminated the need of annual installation of flashboards, enhancing safety, eliminating environmental concerns, and reducinf cost.
- The new design met all current dam safety requirements, was significantly less expensive, had virtually no environmental impacts, could be completed in one construction season, and eliminated future operations and maintenance costs.
- During construction, a team approach involving Nalcor (the owner), Pennecon (the contactor), and Hatch was adopted, which enhanced communications and allowed changes to be implemented seamlessly.
- The Grand Falls spillway was completed in one season, a year ahead of the original envisioned construction schedule and below the original design costs.
- Winner of Award of Excellence in the 2020 Canadian Consulting Engineering Awards.
"Hatch’s innovative engineering solutions for challenging tasks led to cost savings, schedule improvement and successful delivery of this challenging project. This project is an example of engineering innovation that befits recognition."