Auto transport home >> Transport articles >> Bridges Win

Bridges Win

The Ontario Ministry of Transportation (MTO) prides itself on employing consummate professionals in the fields of structural engineering, environmental planning, and individuals who enhance construction projects through innovative and creative design. For several years Road Talk has published a series of articles detailing the progress and completion of a challenging contract that demanded the skill, creativity, and innovation from a team of MTO professionals: the construction of twin bridge structures carrying Highway 417 across the Mississippi River in Ottawa Valley. It is with great pride that we announce the 417 team's recent acceptance of a 2002 Amethyst Award for outstanding achievement in the service of the Ontario public.

Ontario Premier Dalton McGuinty presented the award to members of the 417 team at the Amethyst Award ceremony on April 21, 2004. The ceremony took place at Toronto's Winter Garden Theatre and was attended by recipients from various government ministries. Amethyst Awards are granted annually by the Ontario Ministry of Citizenship and Immigration in recognition of exceptional work by members of the Ontario Public Service. "In constructing this significant bridge across the Mississippi River, the project team overcame a number of environmental, seismic and structural challenges, addressing each one in a way that set a standard for engineering undertakings within and beyond Ontario's borders," commented Carl Hennum, MTO Assistant Deputy Minister of Operations.

The Highway 417 bridge project was launched in the fall of 2001, in response to increasing traffic volumes and collisions on Highway 17, a segment of the TransCanada Highway running westerly through the Ottawa Valley, near Arnprior. The project team faced a difficult task, as the Mississippi River wetland, a location defined by a number of environmental and geological obstacles, was determined to be the only viable construction site. The wetland featured a diverse fish and reptile habitat; therefore, the team needed to devise a structure that would minimize disturbance to this sensitive ecosystem. Furthermore, construction was complicated by the site's weak, compressible clay soils and a problematic floodplain on the river's east bank. The crossing site was also identified as having the highest seismic zone classification in Ontario. This challenged the design team to develop a structure able to withstand severe seismic forces.

Through preliminary and detail design phases, the team developed effective solutions to the various challenges. The initial research and planning stages involved cooperation from a number of organizations.

"Our clients included the Federal Government, many provincial agencies, the Friends of the Mississippi River Wetlands, and the general public," explained Phil Pawliuk, Area Engineer. "Public Involvement Centers were held at key stages to allow the local farming community, general public and other agencies to participate in both the planning and design phases of this project."

Several design innovations allowed the twin bridges to co-exist with the wetland ecosystem. Bridge piers, minimized both in number and size, and were constructed outside of the river to allow for an undisturbed fish habitat. Several construction measures were taken to compensate for habitat loss and enhance the existing diversity of the wetland (see Road Talk, August 2000). These measures included an aesthetic thin deck design which allowed for a lighter structure and improved shading effects on wetland vegetation; a structural design which preserved water quality by diverting deck drainage to a water management facility; and a deck height facilitating both wildlife movement and recreational trail use below the bridge construction was aided by the creation of a unique temporary access road, composed of rock layers and plastic mesh, which effectively "floated" across the organic layer of wetland with minimal environmental disturbance. The final bridge incorporated an innovative design that left no significant footprint on the Mississippi River wetland. Construction of key bridge elements was scheduled for the fall and winter to minimize effects on aquatic wildlife and migratory birds.

The project team compensated for soil deficiencies by increasing the planned bridge length, and by making use of lightweight fill materials and wick drains (plastic cores that draw water from the soil) in construction. These methods controlled the settlement of bridge approach embankments and reduced the pressure applied to layers of surface clay (see Road Talk, November 2001).

Lastly, the team's creative efforts compensated for the seismic site conditions by incorporating dynamic isolation bearings technology (see Road Talk, May 2001). This design method distributes seismic pressures to multiple substructure units, making the bridge resistant to strong earthquake forces. The team developed a unique hybrid of available systems in order to meet the specific requirements of the Mississippi River site.

"With the cooperation of all parties involved we were able to construct a safe and economic structure while minimizing environmental impacts," said Nicolas Theodor, Senior Structural Design Engineer.