Canadian Consulting Engineer

Feature

Sea to Sky Highway Test Section

As part of its preparations for the 2010 Winter Olympics, the B.C. Ministry of Transportation is upgrading the Sea to Sky Highway between West Vancouver and Whistler. The corridor is not only a vital...




As part of its preparations for the 2010 Winter Olympics, the B.C. Ministry of Transportation is upgrading the Sea to Sky Highway between West Vancouver and Whistler. The corridor is not only a vital link between future Olympic venues, but it also serves a number of communities who will benefit in the long term from the upgrades. The existing road is primarily a two-lane, winding route that allows vehicles an average speed of about 55 kilometres per hour.

This is extreme terrain even in the context of the mountainous province of British Columbia and the project faces immense challenges. Steep, near-vertical cliffs overhang the highway in many spots and unstable rockfill slopes reach down to the CN Rail line and the ocean below.

The B.C. Ministry of Transportation initially retained Associated Engineering to complete the preliminary design of Section 2 of the Sea to Sky Highway, from Sunset Beach to Lions Bay. However, realizing the upgrades would require groundbreaking design and construction methods, the consultants worked with the Ministry to first identify a test section to confirm that the corridor could be upgraded safely and with minimal environmental impact. The construction also had to be done with minimal traffic closures. The identified test section, one kilometre long from Montizambert Creek to Strip Creek, incorporated all the toughest challenges to be solved in upgrading the highway.

To investigate, design and construct the test section, the Ministry retained Associated Engineering as prime consultant, Golder Associates as geotechnical subconsultant and Emil Anderson Construction as contractor under a “modified alliance” contract. All the parties worked interactively to optimize and update the design as construction progressed.

The test section was successfully completed on time and 30% below budget. The result is a constructible, economical, four-lane highway which passes around and over cliffs, and above a rail line and residential roads below. The project lays the foundation for the successful upgrade of the remainder of the Sea to Sky highway.

To complete the upgrade from two lanes to four, while keeping lane closures to a minimum, it was necessary to minimize blasting on the slopes above the highway. This meant placing the alignment as close as possible to the existing upslopes, while still maintaining four full lanes plus shoulders that would safely accommodate cyclists and disabled vehicles.

The team reduced the width of the roadway cross-section by designing a unique cast-in-place barrier system that narrowed the land requirements by one metre. Yet this was still not enough to accommodate the roadway within the tight confines of the site.

To address this shortfall, two concrete “half bridges,” called “downslope structures,” were designed for the cliff sections. The design and detailing of these structures were instrumental in allowing the four-lane highway to be constructed around the rock cliffs.

In areas on steep bedrock, the team designed an innovative hybrid retaining wall system. The wall uses precast concrete panels as the facing component of a mechanically stabilized earth (MSE) system, with strong polymer geogrid layers cast directly into the concrete panels. The concrete wall panels are in turn supported on cast-in-place concrete “starter” retaining walls, which are anchored into the bedrock. The hybrid system allows wall heights approaching 15 metres high, three times the height normally used for MSE walls in B.C. It is the first known application of such a wall system on such steep mountain terrain in North America. The hybrid wall approach with various MSE systems will be used along the whole 100 kilometre corridor.

In areas of unstable rockfill slopes, the team used wire-faced, “green” MSE retaining walls. The system features high-strength polymer straps fastened to a wire facing. It transforms the retained soil mass itself into a “gravity” retaining wall and allows vegetation to thrive, such that the walls will become green, natural features. The use of MSE walls on existing fill slopes is unique. A displacement-based, non-linear seismic analysis showed that the wall system design accommodates settlements in the existing fills and is therefore earthquake resistant.

Geotechnical input was a crucial component of the design. The foundations and rock anchors were designed according to the specific geotechnical conditions encountered as construction proceeded. The approach required careful mapping of the fault and joint zones. In many cases, unstable slopes required structural solutions to transfer the loads to sound rock below.

Protecting the natural environment was an important goal and overriding principle. The design minimized the use and movement of construction materials beyond the site limits, for example. As well, fly ash, a byproduct of thermal power generation, was used to replace cement powder in the concrete. Minimizing lane closures during construction reduced the greenhouse emissions of idling vehicles and reduced the impact on residents and the natural environment.

Name of project: Sea to Sky Highway Test Section, B.C.

Award-winning firm: Associated Engineering (prime consultant) with Golder Associates (geotechnical subconsultant), Burnaby, B.C. (Don Kennedy, P.Eng., Norm D’Andrea, P.Eng., David Harvey, P.Eng., Shaun Bidulka, P.Eng., Brian Mylleville, P.Eng., David Tyler, P.Eng., Paul Schlotfeldt, Ph.D., Tom Tasaka, P.Eng., Ed Gohl, Alfred Kao, P.Eng., Julien Henley, P.Eng., Mingyu Li, P.Eng.)

Owner: B.C. Ministry of Transportation

Contractor: Emil Anderson Construction

Other key players: SNC-Lavalin (owner’s engineer); CH2M Hill (owner’s construction coordinator)

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