The following are edited excerpts from Glacier Skywalk (Figure 1 Publishing) by Clea Sturgess, Trevor Boddy, and Jeremy Sturgess, available April 2017.
Over the Sunwapta Valley, in the heart of the Rocky Mountains and at the apex of the Great Divide, a man-made structure balances from the edge of a cliff to give an unprecedented view of glacier, mountains, and valley.
Virtually invisible from the Icefields Parkway, Glacier Skywalk’s cantilevered glass-floored walkway inspires simultaneous terror and delight when visitors realize they are suspended over a precipice with no visible structural support. This is the climax of a journey that winds its way along the mountainside, with stops that interpret, hide, and reveal the astonishing natural surroundings.
The project began in the fall of 2010, when Brewster Travel Canada asked teams of engineers, architects, and contractors to compete to create a vision for a new attraction on a site in Jasper National Park. Parks Canada had precipitated the idea for this competition through a call to companies like Brewster to envision new attractions that would encourage tourists to get out of the car and embrace nature and the realities of climate change. The primary goals were to manifest the structure into a man-made extrusion of the landscape and to weave a series of macro experiences that would link the 300-metre distance from the bus stop to the Skywalk bridge as a journey in itself.
The competition process, the scale, the context, and the unprecedented type of building inspired innovation and cooperation from all members of the team. The site offered a rare combination of natural setting to capture visitors’ interest and imagination, rich cultural and ecological history to inform the design, and provide interesting learning opportunities, and previously developed land to minimize the impact of new construction.
The process that ensued was an extraordinary collaboration of client, Parks Canada and government personnel, consultants, contractors, and manufacturers, each one a champion for what had become the project of a lifetime.
From Proposal to Construction: Building Glacier Skywalk
The Glacier Skywalk construction process had to be carefully planned to be as efficient as possible on a fixed budget and to minimize the impact on the environment. Skywalk sits on land previously disturbed during the construction of the Icefields Parkway, and Parks Canada had already designated the land for outdoor recreation to promote understanding, appreciation, and enjoyment of the park’s heritage. But projects like this, involving cliffside excavation, wilderness conditions and steel cantilevers, are rarely undertaken, and the construction team had to consider many things it had never seen before.
The first plan was to build the whole thing in one season, which turned out not to be feasible for two reasons. First, the harsh winters limited the construction season to just six or seven months. Second, a wildlife impact study found that the kidding season for the mountain goats and bighorn sheep that live in the area takes place from May to July and that having people and equipment around at certain times would interfere with that natural cycle. Fifteen cameras were set up around the site to monitor the animals’ movements, and ultimately it was decided that Glacier Skywalk would have to be built between July and October only, over two alpine summers, and only outside of the morning and evening hours during which the goats use the area. The monitoring continued through the construction phase and is still ongoing. An environmental assessment study also reviewed the concept of Glacier Skywalk and its construction, ongoing operations, traffic management procedures and impact on wildlife and ecosystems, as well as the cultural history of the area and future requirements associated with the project.
Setting the Foundation
The construction crew began by building the major structural components—the platform foundation—including the steel girders that would support the structure of the Skywalk bridge. Initially, core samples of the rock were taken at four locations of the Skywalk site and visually inspected to review the rock quality. In the lab, the samples were tested for load (their ability to hold the weight of the structure), compressive strength (their ability to resist breaking when squeezed under load) and direct shear (their ability to resist breaking when squeezed in two opposing directions).
Once the rock had been tested, construction began. Erosion-control equipment was installed on site to protect the existing rock bed, and an anchor chain-link fence was placed on the side of the cliff to prevent rocks from falling into the valley below. Crews blasted rock out of the cliffside and drilled rock anchors into the ground. Once the foundation anchor rods—threaded bolts with a nut and washer at one end—were in place, foundation footings were formed to support the load and reinforcing steel was installed to strengthen the concrete. Stress plates were then installed onto anchor rods to mitigate the stress of minor movements, and structural steel bearing plates were added. Concrete was then placed, finished, and cured in one continuous operation.
While the foundation for Skywalk was being set, a demolition contractor drilled blasting holes three metres deep to form the pathways along the cliff, and the fractured and blasted rock was excavated from the foundation using a hydraulic excavator.
Crafting the Components
Assembling a structure like Skywalk in such a small space required the design and engineering teams to work closely together before and throughout construction. This involved thinking through what could be built off site beforehand and how best to assemble the pieces at the site. The metal structure that underlies the glass walkway was prefabricated in six pieces in Edmonton, trucked into the future bus pull-off/parking lot at the top of the site and welded together. All the welds were x-rayed and analyzed to ensure their integrity. Crews used a 318-tonne crawler crane and a Superlift lattice boom crawler crane to lift the massive pieces into place.
Building the Structures
The load-bearing structure of the bridge was transported as one unit on a low loader trailer from the pre-assembly area to the installation site 500 metres away and lifted into position in one piece. After the bridge was bolted to its anchors and all bolt and screw connections had been closed, the bridge was lifted into the proper position so that the steel tension cables, located in the two large circular tubes behind the glass, could be inserted and tightened. After the pre-tension in all ropes was uniformly adjusted, the bridge became self-supporting. And since the Skywalk bridge is extremely sensitive to vibrations due to the combination of the support structure’s flexible joints, the pre-tensioned cables, the light construction and the exposed site in the high mountains, four mass vibration dampers were installed and blocked to the steel construction below the walkway to prevent the bridge from moving too much when people walk over it. After the glass floors and balustrades were installed the vibration dampers were calibrated by means of sensors attached at various points along the bridge.
With the bridge installed, crews began bolting the Cor-ten steel cladding to each of the underlying steel components. For example, adjacent to the rock wall, a structural steel framework was bolted to the structural steel trapezoidal girders. Once that framing was installed, Cor-ten was attached to the framework. As the cladding reached the rock wall, it was periodically adjusted to obtain an adequate fit.
The kiosk and pathway, including the nodes, and the architectural features of the Skywalk bridge were built last. After the complicated process of excavating, blasting and assembling the bridge, the rest of the project came together very quickly.