Geoweb Slope Protection for Stormwater Pond

LOCATION: Conklin, AB

TIMEFRAME: Project start /end - Feb. 4, 2011 to March, 2011

SCOPE OF WORK: Provide slope protection for a 21,000 cubic metre capacity Stormwater Pond with clay liner and 3H:1V slopes

PROJECT PARTNERS Owner: FCCL Oil Sands Partnership (Cenovus Energy and Conoco Phillips) Client: Browns Bobcat Service Installation: Browns Bobcat Service Material supplier: Layfield / Presto Geosystems

Challenge

The original slope protection for the Stormwater Pond slopes at 3:1 was designed as an emulsified asphalt layer over 300 mm of 50 mm minus sandy gravel over Tensar BX 1100 geogrid. This design was considered technically questionable and expensive by the client, so Cenovus and their Engineer - Vista - IMV Joint Venture requested Layfield to provide a Geoweb alternate. Construction was to be in winter 2011.

Solution

The Engineer Vista-IMV Joint Venture provided Layfield with a completed project evaluation form and a full set of drawings of the pond showing the existing design. Assumptions and additional data were added by Layfield and based on this a preliminary design drawing was provided by Presto Geosystems (key portion shown below). Also, the SPECMakerR tool was utilized to produce a full materials and construction specification.

The design called for 150 mm thick GW30V6 Geoweb secured in place by 600 mm long Atra Anchors at the spacing noted above. The Geoweb cells were specified to be filled with a nominal 50 mm (clear) stone. The Geoweb was placed on a Layfield LP10 nonwoven geotextile underlay.

Based on the drawings, Layfield estimated quantities for supply of 481 Geoweb sections 2.6 mX 6m and 241 sections 2.6m X 7.2 m, for a total supplied Geoweb area of 12,015 m2. The supplied materials also included 10,584 GFRP (or Glass Fiber Reinforced Polymer) Atra Anchors with Atra Clips (supplied as one piece), 22,950 Atra Keys and 35 rolls of LP10 nonwoven geotextile (14,651 m2).
The quoted and secured price for this package including delivery was $ 199,169 (excluding tax) which works out to $ 16.58 per square metre of slope protection supplied.

Results

The Geoweb was delivered in January, 2011 and installed by Browns Bobcat Service.
Installation began in early February, 2011 with temperatures ranging well under -20 degrees Celsius. The LP10 geotextile was placed first and anchored at the top in an anchor trench. The Geoweb was placed and connected together with Atra Keys. Due to the frozen ground the holes for the Atra Anchors were predrilled using long steel drills. Then the GFRP Atra Anchors were hammered in and the Geoweb was filled with granular backfill. Considering the unfavourable weather, the installation went fairly well.

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