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Steep gradient formwork challenge Oct 2011
Peter Kenyon, TunnelTalk
Ceresola has been commissioned by Redpath/FKCI Waneta Tunelers, consisting of Redpath and Frontier-Kemper, to overcome the tough challenge of supplying a full round formwork to cast the lining of a 17% gradient, 400m of hydro intake tunnel for the CAN$900 million Waneta hydro expansion project in British Columbia, Canada.

Formwork for the headrace alignment supplied by Ceresola is 7.5m long, 10.52m diameter, and weighs 135 tonne

The Swiss formwork supplier has designed a hydraulic solution to operate the 10.52m diameter full-round forms, each of which weighs 135 tonne. This is an unusually large diameter for formwork of this type, and, coupled with the near 1-in-5 steep gradient, demands special safety considerations.

Fig 1. Plan of the Waneta hydro expansion project

For this reason a conventional cable method of lowering the formwork into place could not be used. Ceresola has devised a step-by-step hydraulic solution instead.
Each of the steel segments is 7.5m long. They will be fitted into two 200m long intake tunnels, which are already under construction at the site.
Assembly of the 20m hydraulic traveller which is being used to move and position the formwork precisely is due to begin in November. A concrete placer is also included in the scope. The system was designed in Switzerland and produced and pre-assembled by Ceresola at its Northern Italian plant. The full-round formwork was accepted by the client in September following an intensive three day inspection.
At the start of 2012 the formwork is to be put into operation on the construction site in Canada.

Fig 2. Artist's concept of the finished project

The Waneta hyro expansion project is owned by a partnership of Crown Corporations the Columbia Power Corporation (CPC), and the Columbia Basin Trust (CBT), in partnership with Fortis. CPC is acting as Project Manager. Together they have formalized a design-build contract with SNC-Lavalin to act as the contractor.
The project began last year and when complete in 2014-15 will see the construction of a secondary 335 MW powerhouse immediately downstream of the existing Waneta Dam.

Aerial view of the existing layout

A major part of the project is the excavation of two new parallel 200m long tunnels that will supply two Francis turbines in the newly constructed powerhouse (Fig 1). Excavated rock is being quarried within 7km of the site and will be available for re-use in future highway and infrastructure projects in the area. Blasting operations in the tunnels, which continue six days a week, are expected to be complete by March next year (2012).
Also included in the scope is a 10km transmission line to be built parallel to the existing BC Hydro high voltage line from Waneta to the Selkirk Substation.

           

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