Dissette Street Widening and Reconstruction
The Dissette Street Widening and Reconstruction Project, started in mid 2010 in Bradford Ontario. It had several unique features that set it apart from other projects of its kind. Chief among those unique design considerations was the need for the structure to be a vegetated green wall system since the project was to be so closely located on the north side to sensitive conservation lands. Because of this need, the engineering firm of RJ Burnside out of Newmarket, Ontario designed the 264 meter long wall, which ranged in height from 3.5 to 8.6 meters , with Maccaferri’s Green Terramesh product. This product is a prefabricated modular system made from hexagonal double twisted wire mesh and used to reinforce the 60 degree slope. This final design was stamped by the firm of Chung and Vander Doelen. North Rock Group was chosen as the GC and Rocky River Construction did the installation.
Issues arose over the course of the project requiring close attention to detail pertaining to the wall footings due to the weak soils on the site. This required careful consideration for the design and engineering of the foundation for the wall. Once these issues were successfully resolved the Green Terramesh was installed and backfilled with a granular b material.
Biotic Earth Black, a Biotic Soil Amendment, was applied to the exterior of the Green Terramesh system at an application rate of 3,500 lbs/ ac to account for the minimal amount of fine soil particles in the soil layer on the near vertical system. Biotic Earth Black is ideal for situations where topsoil quantity or quality is marginal due to the product’s water and nutrient storing capacity. It is also a good addition for situations where vegetation is needed but a topsoil layer is lacking entirely. Another feature the Biotic Earth provided for this project was the promotion of the much needed soil “life”: the mycorrhizae and bacteria needed to create a sustainable stand of vegetation. Biotic Earth Black allowed for a perpetually lush stand of vegetation on the site and continues to support it in successive years.
Fibramulch hydromulch was chosen for the final layer in this system and applied on top of the Biotic Earth Black by Dol Hydroseeding. This product was chosen for this site due to it’s ability to be used on severe slopes and it’s lower than average water needs for application; allowing for a 25% faster installation time. “The Biotic Earth sprayed nicely into the crevices, and then the Flex Guard really trapped it in place to the surface.” Said Peter Etherington of Fibramulch.
Flexibility is excellent in green wall systems such as the one used on this project. Unlike block walls or other hard armor systems where seams or joints must match up exactly to be visually successful, green armor systems are more forgiving while maintaining the aesthetic integrity of the project. This was especially important on the Dissette Street Widening where care needed to be taken with the wall foundation. Using a green wall in this instance allowed for flexibility due to specific site conditions while maintaining excellent visual integrity.
“Not only do you get the site specific structure you need, you also get the vegetation you want- it’s the best of both worlds” said Santino Tersigni of Maccaferri Canada, Ltd.
While maintenance costs are often assumed to be higher on green wall systems; the opposite can actually be true. Consider the cost and difficulty of replacing individual cracked or damaged segmental blocks from a standard wall structure- these ongoing maintenance costs are often overlooked when hard armor systems are used. Also overlooked entirely, is the benefit that green wall systems have no graffiti or similar vandalism concerns; a good design option for areas with those perpetual issues arise within a municipality.
The green wall that was installed on the Dissette Street Widening Project successfully combined all of the particular needs beautifully for this site. It provided the vegetated system needed due to the adjacent sensitive lands, the structural integrity required for the design, the flexibility needed due to the discovered weak soils on site, and the aesthetics required in the finished product. Green walls truly do fulfill a needed niche in our construction industry, and with technological advances in the products used in their implementation over the past few years they are becoming an increasingly viable option in our industry.
By Rene Barrientos