September 30, 2011

WIKIMEDIA COMMONS and ONTARIO POWER GENERATION

The Otto Holden Station on the Ottawa River was built with 300,000 cubic metres of concrete poured over four years starting in 1949. An assessment in the late 1990s found concrete deterioration, triggering rehabilitation plans.

FEATURE | Concrete/Masonry

Ontario Power Generation refurbishes concrete at Otto Holden Station hydro plant near Mattawa

PETER KENTER

correspondent

Originally named LaCave, the Otto Holden Station is a 240 MW hydro generating station located on the Ottawa River near Mattawa.

Construction of the massive concrete dam and sluice gates was initiated by the Hydro-Electric Power Commission of Ontario in 1949, with 2.7 million tons of earth excavated and 300,000 cubic metres of concrete poured over four years. The station went online in 1952.

To ensure Otto Holden continues to be a reliable source of clean renewable energy, Ontario Power Generation (OPG) is refurbishing the concrete structure. Phase One of the rehabilitation, which began in 2000, includes concrete alkali aggregate reactivity (AAR) mitigation — replacing concrete decks on the gravity sections of the dam, sluiceway decks, stoplog decks, sluiceway and tailrace piers, and transformer beams. Total value of the project: approximately $80 million.

The dam was built during a massive period of hydro-electric system expansion in the province. It was one of three similar projects built in the area at the same time, as crews built one project after another, foundation crews moving from project to project as other construction trades followed.

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A condition assessment of the site in the late 1990s revealed concrete deterioration. The upper concrete portion of the plant was also moving relative to the stationary components fixed to the section below.

“Usually you would see simultaneous movement of the entire mechanical system,” says Ed McColm, P.Eng., project site manager with OPG Otto Holden.

The movement resulted in such problems as reduced sluice gate capacity, misaligned mechanical systems and reduced clearances for draft tubes.

The misalignment is caused by the effects of AAR, which causes concrete to expand over time. With the west side of the dam firmly anchored in the bedrock of the shoreline, the concrete is swelling and expanding eastward.

During Phase One remediation, engineers devised a way to move the lower mechanical components relative to the upper parts using a moveable pivot ring design.

“Some of the components were modified and can now be moved incrementally as the top section shifts,” says McColm. “They can keep doing that until they run out of room and a new solution is employed.”

The concrete work is taking place primarily at the water line and above, as the cold waters at the base of the dam provide a static environment for the concrete.

The primary roadway surfaces on the sluiceway decks had also deteriorated, resulting in loading and traffic restrictions on the deck and operational restrictions on log lifters, which provide discharge capacity at the site. The deteriorated top surfaces of the dam have been taken down to as much as 45 cm to sound concrete and then resurfaced.

Sluice gates are also being replaced. The project started with repairs to the pier nose followed by sandblasting and painting of the superstructure with installation of a new electrical system. The six individual gates are being replaced at a rate of one per year.

Service and product suppliers for the massive project have included ABB Inc., Acres International, Aecon Construction, Alstom Power Canada Inc., COH Cranes, Comstock, Cutler-Hammer, Johnston Pumps, KGS Engineering, Kinectrics, KST Hydroelectric Engineers, Larco Cranes, Orbit 3 Electric Projects, RSW Inc., Unifin International, VibroSystM, Walter Construction and Westinghouse.

The Phase One project is scheduled for completion in November 2012. Phase 2, expected to commence in 2014, will include both mechanical and concrete work, including remediation of additional sluice gates.

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