This paper documents the construction and settlement monitoring of an 18 m high roadway embankment that was constructed over two gravel quarry wash ponds for James Walker Trail located in Cochrane, Alberta.
The primary objective of the work was to ensure that embankment settlement would not adversely affect the performance of the future roadway/pavement structure. In addition, the project focused on reducing the amount of imported backfill and reusing available on-site soils.
The key challenge of the project was determining how to reuse the existing wash pond sediment to safely construct the embankment without adversely impacting the future roadway performance. The existing pond sediment consisted of wet, fully saturated, soft, sandy silt, varying between 2 m and 5 m thick with an estimated volume of up to 50,000 m3.
The optimized simple design approach and proposed construction plan consisted of using a combination of geotextiles for soil stabilization and installing a drainage blanket connected to multiple drain outlets to drain the excess porewater out of the pond sediments during and after construction. The existing wash pond sediment material was able to be left in place and was reused as part of the embankment structure, thereby reducing the need to remove the pond sediment and import new fill.
The roadway embankment fill was subsequently placed in a staged approach to allow construction to continue safely while monitoring porewater pressure and settlement using a series of vibrating wire piezometers, vibrating wire settlement gauges, and settlement monuments. The embankment fills also reused reclaimed cobbles/boulders and on-site available soils including clay, silt, and sand to reduce the amount of import fill required.
The project was successful in reusing the estimated 40,000 m3 of pond sediment, reusing available on-site soils, and minimizing the amount of import fill required. In addition to the cost savings related to these activities, several environmental benefits were also indirectly realized. Energy use and carbon emissions decreased due to reduced construction equipment operation and hauling activities associated with the pond sediments (i.e., up to 80,000 m3 for the exporting of pond sediments and importing of new fill). Reusing on-site soil materials also reduced the environmental footprint of the project by minimizing the need to extract more fill from other sites, disposal of pond sediments, and reduced hauling activities along with any associated traffic congestion.