AWARD OF EXCELLENCE / TRANSPORTATION Squamish Pedestrian Overpass
October 1, 2013
By Hatch Mott McDonald
“A delightful small project, this bridge demonstrates tremendous sensitivity to its context and gives expression to the history, art and culture of the Squamish Nation.”
Hatch Mott MacDonald (HMM
) was retained by the British Columbia Ministry of Transportation and Infrastructure to design an overpass to span the Sea-to-Sky Highway and a CN Rail track near Squamish, B.C., about 50 kilometres north of Vancouver. HMM was responsible for project management, concept development, detailed design, and construction support.
The overpass connects one side of Squamish Nation land to the other, and the key goal of the project was to provide safe passage across the busy highway and track. Before the bridge, pedestrians had to cross at grade. The bridge also had to be a unique and meaningful structure that honours the native community and blends with the natural environment.
The overpass had to concurrently address the needs of the local community, meet BCMOTI standards, contend with technical site challenges, and maintain a strict budget.
HMM consulted and collaborated with many stakeholders during the design, including the Squamish Nation, the Squamish Lil’wat Cultural Centre, BCMOTI, CN Rail, and BC Hydro.
Slaying the Serpent
Squamish cultural features created by Squamish Nation artist Xwalacktun grace the overpass. The aesthetic components were integrated seamlessly into the structure, adding visual impact without adding significant cost.
The overpass’ “thrust walls,” for example, capture the Squamish Nation tale of “Slaying the Serpent.” The spear-shaped bridge hangers and struts reinforce this theme, and mask the bolted connections from view. The 16 hangers and struts represent the 16 hereditary chiefs of the Squamish Nation.
On the reverse of the thrust walls the symbolic Thunderbird is represented. And a pair of upturned paddles greets travellers from the west, symbolizing peace and respect. The blue-grey colour of the arch represents the story of the “Great Flood” in Squamish folklore.
and a flattened arch
The bridge structural design was governed by difficult soil conditions, overhead clearances to high-voltage power lines, and other property and site constraints.
The overpass’ arch profile was flattened to maintain sufficient clearance from the overhead power lines. This flattened profile necessitated the use of thrust walls at the east side of the highway to support the arch at height. These thrust walls in turn became a giant canvas for Xwalacktun to cast his relief patterns into the sides. The steel main arch was fabricated ahead of time to speed placement during construction.
A trail connects the east end of the overpass to the Stawamus Elementary School. Stacked walls support the trail as it drops down a moderate elevation from the main arch. The terrain proved to be difficult, and the alignment had to be iterated multiple times to keep the maximum grades below 1:12 while minimizing the amount of excavation and fill.
The overpass incorporates an observation deck, which provides a rest area for pedestrians to pause and enjoy expansive views of the surrounding mountains.
The project illustrates how engineering efforts must satisfy disparate requirements. Its successful completion exemplifies how engineers not only build infrastructure to serve our communities, but also help to build pride in those communities. cce
Award-winning firm/prime consultant:
Hatch Mott MacDonald, Vancouver
(Schaun Valdovinos, P.Eng.; Tony Martin, P.Eng.; Jamie McIntyre, P.Eng.;
Thomas Chiu, E.I.T.)
BC Ministry of Transportation
Other key players:
(construction); DMD (lighting and
electrical); Xwalacktun (artist);
Squamish Lil’wat Cultural Centre ; Xwalacktun (artist); CN Rail, BC Hydro.