Canada’s northern forested landscapes feature numerous wetlands, such as fens, bogs, and swamps that present environmental and operational challenges for resource roads. The effects of these roads on the many ecological functions of wetlands are of increasing concern to Canada’s resource industries, governments, northern communities, and conservation organizations.
Among the difficulties in the planning and construction of resource roads which cross wetlands are the low bearing capacity of the subgrade material and the placement and installation of adequate drainage and water-crossing structures. However, both wetlands and resource roads should be able to function with careful planning, knowledge of the various wetlands and their ecological functions, and the development and use of best management practices.
FPInnovations, in partnership with EACOM Timber Corporation, undertook a study to assess a method for improving culvert foundations (Partington 2014, 2015). At the study site, the poor bearing capacity of the deep organic soils is a particular challenge that required improved culvert foundation techniques. It was known that in other areas of Canada biaxial geogrids have been used in an attempt to reinforce the culvert foundation. The forest company and contractor decided that at this site, since the geogrid was going to be used as subgrade reinforcement in the road, it would also be installed directly under two of the culverts while the remaining culverts would be installed on the forest floor with no provision for an improved foundation (see Figure 1). On soft, compressive soils like this, the entire road embankment is expected to settle; the amount will depend on the fill thickness (i.e., total mass of the fill) and on the bearing capacity of the native soils. Geosynthetics are often used to help minimize differential settlement by bridging weaker sections along the road. It was believed that the geogrid could act as a type of hammock by supporting the culvert and preventing any significant settlement due to the dead load of the road fill material. In addition, a woven geotextile was placed under the geogrid, a practice that was standard for the operations at this site.