Case Studies

Wismer Commons Triple-Cell Con/Span Culvert

Markham, Ontario

Con/Span culverts and bridges are identified as proven systems for road crossings of significant wetlands, fisheries, and environmentally sensitive areas. The three-sided precast concrete arches, that characterize Con/Span installations, are included often in servicing reports and environmental studies as possible solutions to servicing issues. Many contractors, consulting engineers and owners of projects favour the systems to facilitate permitting from federal, provincial, and local environmental authorities. The arched system can be installed very quickly with limited disturbance to riverbeds and floodplains.

The 386-hectare (955-acre) Wismer Commons Planning District in Markham, Ontario is a development project where Con/Span systems were identified as possible culvert structures very early in the design stage. When fully developed, the planning district will comprise residential subdivisions, schools, parks, commercial sites, and open space systems to accommodate a population of 21,000.

Most of the land in the planning district drains to the west and east branches of Robinson Creek, a tributary of the Rouge River that flows south to the City of Toronto and Lake Ontario. The west branch drains a large external area of 660 hectares, characterized by a moderately to gently sloping topography. Since the West Robinson Creek is a defined valley system, the current channel alignment and configuration was maintained in the stormwater management design, except for a section near the confluence with the east branch where a stormwater management pond is sited. The well-defined valley provided opportunity for the phased servicing of arterial connections with existing and future communities.

Bur Oak Drive is a major east-west mid-block connector. It will establish additional transit service, linking the communities of Berczy Village and Wismer Commons to developments east of the Wismer Commons Planning District. The road also will provide a high degree of internal connections and local access, as well as linkage with primary roads north and south to maximize transit coverage. The Town of Markham placed a priority on the construction of Bur Oak Drive, and this required a crossing of the West Robinson Creek valley in the early development phase.

Policy statements in the Official Plan for Wismer Commons established guidelines for creek crossings to minimize intrusions and alterations to existing valley landform and function. The siting and crossing of Bur Oak Drive had to address the following requirements:

- Pedestrian and wildlife access in the valley corridor;
- Watercourse dynamics such that channelization and armouring, and the need for future remedial works are minimized;
- Aquatic habitat including the retention and/or establishment of appropriate riparian habitat; and,
- The safe passage of Regulatory Flood flows such that existing Regulatory Flood elevations are maintained to within acceptable limits as determined by the Town and the Toronto and Region Conservation Authority.

All road crossings in the planning district are located in areas where the valley is narrow to minimize loss of riparian storage. The 45.5 metre long (6100 mm x 2130 mm) triple cell Con/Span culvert for the Bur Oak Drive crossing was designed so that no backwater effect would occur under the Regional Storm event. The existing Regional flood elevation would be matched in the post development condition, and the open culvert would provide better fish passage. In addition, the open bottom culvert would protect existing fish habitat and maintain the integrity of the low flow channel and instream cover. The triple-cell culvert would meet the Official Plan guidelines fully, and provide localized wildlife habitat and corridor opportunities, as well as recreational linkages for people.

Construction of the culvert would take place on soils that are associated with the Robinson Creek Swamp headwater area, with parent soil material consisting of sandy outwash over calcareous clay till at depths of three feet or less, and bottom land consisting of irregularly stratified alluvial deposits. Footings had to be engineered to take the weight of the structure, and design loads of the anticipated vehicular traffic.

Balke Engineering Inc., of Mississauga, Ontario worked with Schaeffers, the consulting engineers, Con-Drain the contractor, and the producer of the Con/Span units, Con Cast Pipe, to design a support system for the culvert. The design called for the installation of two hundred 324 mm diameter piles consisting of 12.7-gauge steel and 25 MPa concrete. Four sets of footings were placed over the piles. In addition to supporting the Con/Span units, the footings were designed to lock the units in place and tie into the wingwalls. Once the piles and footings were ready to receive the culvert units, Con Cast Pipe started shipping the product, two pieces per load.

Each of the three cells of the culvert required two (2770 mm x 6600 mm) units, 16 (2380 mm x 6600 mm) standard units, two (2770 mm x 6600 mm) units with headwalls and one (2380 mm x 6600 mm) short unit. In addition, Con Cast Pipe supplied eight precast concrete wingwall units. In all, 57 Con/Span units were supplied to the Bur Oaks Drive crossing. The mass of each of the standard units is 15,860 kg. The units were offloaded from the trucks as they arrived, and installed at a rate of about one every 20 minutes.

A new feature for the culvert was the use of precast concrete coping units that were placed at both ends of the culvert on each side of the centre cell, one on top of the other. Eight coping units were required, four at each end of the culvert. The coping units provide a more pleasing architectural finish to the triple-cell structure.

Con-Drain installed the 57 units over a three-day period during mid January winter conditions using a 400 tonne crane. Within a week of completing the installation, the construction crew had prepared the roadbed, making it ready for pavement in the late spring or early summer of 2001. The speedy installation, with little disruption to the valley land and aquatic habitat assures the municipality that Bur Oak Drive will be ready for public transit as soon as the area is opened for service.

Installation of the triple cell culvert demonstrates the versatility of using precast concrete structures, like Con/Span systems, when construction schedules are tight, weather conditions are severe, and when environmental issues are of great importance. The installation is designed to service the planning district well into the next century. With little maintenance required to the structure, it will be easily assimilated into the natural features of the West Robinson Creek watershed and habitat of aquatic and terrestrial wildlife. It is likely that residents of the area will enjoy the open space system, and give little notice to the function of the structure, appreciating its architectural attributes and safe passage through the town.

The general contractor for the project was Con-Drain of Concord, Ontario. The consulting engineer was Schaeffer & Associates Ltd., Concord, Ontario and Balke Engineering designed the footings. Con Cast Pipe of Guelph, Ontario produced the precast Con/Span units. The construction cost of the triple cell culvert was $950,000.