Project Name: Christina Lake
Project Location: Conklin, Alberta, Canada
Site contractor overcomes construction and weather challenges to install cost-effective 3D GEOWEB slope cover over a 21,000 cubic meter capacity process pond.
PROJECT BACKGROUND:
An original slope protection system planned for 3H:1V process pond slopes was designed as an emulsified asphalt layer over 300 mm (12 in) of 50 mm (2 in) minus sandy gravel over Tensar BX 1100 geogrid. However, the design was considered technically questionable and expensive by the client, so Cenovus and their Engineer – Vista – IMV JV Corporation sought alternatives.
Consequently, Canadian geosynthetics supplier Layfield Group, Edmonton, Alberta was contacted to assess the feasibility of utilizing the 3D GEOWEB Geocell System manufactured by Presto Geosystems as an alternate cover solution. Construction was targeted for the Winter in 2011 which posed some material and construction challenges. The temperatures during this timeframe typically range from -20 C to -30 degrees C.
GEOWEB 3D COVER SYSTEM:
The project engineer for Vista-IMV provided Layfield with a completed evaluation and full set of drawings for the original geogrid design. Assumptions and additional data were added by Layfield’s technical team to account for the GEOWEB solution—and subsequently turned over to Presto Geosystems’ technical team to perform their own preliminary evaluation and cross-section details.
The new evaluation specified the 150 mm (6 in) deep GEOWEB sections secured in place by 600 mm (24 in) long
ATRA® Glass Fiber-Reinforced Polymer (GFRP) anchors placed in GEOWEB cells 1, 5, and 8 and every fourth row down the slope. The corrosion-resistant anchors provided anchorage and resistance to sliding or uplift forces and resist degradation from exposure to acidic soil environments and water. Weather and corrosion-resistant connection ATRA® keys were used to connect GEOWEB sections side-to-side and end-to-end.
The original infill specified for the GEOWEB system was a nominal 50 mm (2 in) clear stone placed over a nonwoven geotextile separation underlayment—later modified to allow a wider range from 25 mm (1 in) to 75 mm (3 in). However, the available on-site fill, an aggregate sand mixture, was allowed as acceptable infill.
PROJECT RESULTS:
The GEOWEB material was delivered to the site in January 2011 and installed by Browns Bobcat Service. Installation began in early February 2011 with temperatures ranging well under -20 degrees C. A non-woven geotextile was placed over the slope surface and anchored at the top in an anchor trench.
GEOWEB sections were placed over the geotextile and connected end to end and side to side with ATRA® Keys. Frozen ground made the driving of the anchors nearly impossible, so holes for anchor placement were predrilled using long steel drills.
After all anchors were secured, the GEOWEB sections were filled with granular backfill. Considering the construction challenges caused by unfavorable weather, the installation went well. Over 12,000 m2 of GEOWEB material was installed for this slope cover project.
Background: Cenovus Energy’s Christina Lake Oil Sands Project
Source: www.cenovus.com websiteThe oil at Christina Lake is about 375 meters underground. It’s so deep that Cenovus Energy has to use specialized technology to drill and pump it to the surface. The technology is called steam-assisted gravity drainage (SAGD). Construction of the pilot project at Christina Lake began in 2000 and first production occurred two years later. The project is expected to operate for more than 30 years.
In 2017, ConocoPhillips sold its 50% interest in the FCCL oils sands partnership to Cenovus.
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