PRODUCT APPLICATION: Erosion Protection: Cellular system shores oil sands tailings pond

Near Fort McMurray, northern Alberta, Syncrude produces nearly 225,000 barrels of crude oil a day. Three years ago, an external sump area was designed to contain the tailing byproducts in an emergency. The dimensions of the external sump area are approximately 38 m x 38 m x 2.6 m deep, with 3h:1v side slopes.

A large amount of water is required for the containment, so a geosynthetic protection system was required to protect the slopes and floor from the water and prevent it contaminating the surrounding area. The requirements for the containment pond’s erosion protection system were complicated by it having to withstand heavy equipment — a 65,000-lb. wheel loader has to periodically come and clean up the sump area. Another challenge was that temperatures range between –10* C to –15*C. Project designer was Kevin Davis, P.Eng. of CoSyn Technology, Edmonton.

The design uses a Geoweb cellular confinement system with concrete infill. The system was developed by Presto Products and the U.S. Army Corps of Engineers. High-density polyethylene strips, ultra-sonically welded at specific intervals, form a structure of three-dimensional honeycomb cells. Installed in expanded form, these flexible panels are then filled with a variety of infill materials. They are used standardly in gravity and geogrid-reinforced retaining walls, for erosion protection in channel linings and slope protection. Depending on the project, variations in hydrologic and hydraulic conditions and aesthetic requirements, the infill material may be a vegetated topsoil, aggregate structural fill, or concrete.

In the Syncrude project a 30-mil hydrocarbon-resistant geomembrane was specified to contain the processed tailings and prevent the material from entering the environment. A non-woven geotextile was first placed over the prepared foundation — a base comprised of oil sand with a CBR value of *6. The impervious geomembrane was placed over the geotextile and the field seams were completed using a solvent weld. A second layer of geotextile was then placed to minimize potential damage to the liner prior to placing the Geoweb system and infilling with concrete. A third layer of non-woven geotextile completed the design.

Approximately 1,800 square metres of 100 mm (4″) deep perforated Geoweb sections were installed on the external sump’s side slopes and floor. Because the underlying geomembrane had to remain impermeable, it was necessary to employ high-strength polymeric tendons to secure the system without stakes.

The tendons were tied around a 75 mm diameter PVC pipe placed in a trench at the slope’s crest and run downslope through pre-drilled holes in the cell walls. ATRA Clip restraining clips were attached to the tendons every four cells to provide the proper load transfer. The secured Geoweb sections were expanded down the side slopes and over the base of the floor, and adjacent sections were connected with a pneumatic stapler.

Article supplied by Presto Products, distributed by Armtec Construction Products, Edmonton.