February 20, 2012

Wind farm requires 40,000 tonnes of crushed rock

JESSICA KRIPPENDORF

correspondent

NANAIMO

Construction on what could be Vancouver Island’s first wind power generation project is scheduled to begin in June with 30 kilometres of access roads, which will require almost 40,000 tonnes of crushed rock pulled from the site and adjacent quarries.

The $280 million project will spread out over 1890 hectares and will include up to 50 wind turbine generators (WTGs), access roads and transmission lines, located 11 km north of Holberg and 45 km northwest of Port Hardy.

The WTGs will produce up to 100 megawatts of wind energy—enough to power 30,000 homes.

The development will use crushed rock from quarries, and additional road base materials will come from cut and fill activities related to the project.

This will simultaneously create a flat construction lay down area. 

About 3.75 cubic meters of crushed rock will be required for every meter of new five-meter-wide road, said Mark Grant, government relations and public affairs for Rupert Peace Power Holdings.

The project’s developer, Nomis Power Corporation, is under the management and direction of Rupert Peace Power Holdings, a privately held company.

At the site of each turbine, the access road width will increase to allow a foundation to be constructed alongside the road.

“A significant portion of the proposed new access route is located within wet and boggy ground,” said Grant. “Although additional rock may be needed in these sections, the average gravel depth of 0.75 m is expected to be a realistic average as the road construction on solid, rocky ground requires approximately 0.15 m of rock.”

The scope of the construction also includes two 9,200 L portable concrete batching plants to supply concrete materials for the WTG foundations, quarry sites and spoil areas, including a quarry off-site along the Nahwitti forestry road that will supply sand and gravel for the turbine foundations.

All quarry materials will be processed on site for the batching operations.

Nomis will pour a catchment area, where the batching will occur to guard against any seepage or flow of cementitious debris into nearby watersheds or bogs.

This area will be about one acre total.

It will need to be staged at different elevations for easy access of trucks and the washing that occurs between ready-mix loads.

The environmental assessment certificate awarded in December identified a moderate seismic risk for the region, requiring specific shape and reinforcement considerations for the WTG foundations.

“The level of shaking associated with this area could potentially dislodge loosened or detached rocks, leading to a landslide, rock fall or avalanche,” said Grant.

Each WTG will have automatic seismic sensors designed to detect ground vibration located in the steel tower.

The sensors will stop turbine operation past a predetermined set point.

Designs will incorporate structure weights, uplift and horizontal forces potentially caused by an earthquake to prevent structure failure of the WTGs and substation facilities. 

The tower foundations will either be anchored to bedrock or will be reinforced using concrete spread footings in square, octagonal, or cross-shaped configurations.

Depending on geotechnical conditions, the square type foundation may be up to 10 m x 10 m and 3 m in thickness.

A cross-shaped foundation would require four strong ribs to increase the stability against overturning.

“In this case, heavily reinforced ribs of approximately 12 m x 1 m x 3 m in thickness are joined at the top by a reinforced concrete pad of 1 m to 2 m in thickness,” said Grant.

The exact location for the foundations will be determined by site-specific geotechnical site constraints.

“The potential hazards for these types of events are low for most areas on the Nahwitti plateau due to the subtle relief – all of the project infrastructure will be constructed in areas of low relief,” he said.

The WTGs will be laid out in clusters, each with a generator.

Construction and staging requires an area with up to a 60-metre radius for each generator.

Work on the foundations will begin June or July with the WTGs erected between August and October.

Commercial operation is scheduled for the end of the year.

The scope of work also includes a cluster substation and 18 km of underground collector system cables to direct power from the transformers to the substation, then to a shared high voltage transmission line.

Construction will employ 120 workers at the peak, including crane operators, electricians, iron workers, heavy equipment operators, health and safety personnel, and engineers over 18 months.

The construction and erection of the WTGs on site will employ about 20 people for a year.

The remaining 160 person years of work will be related to roadbuilding and site preparation.

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