Challenge

Mining the Athabasca oil sands involves removing the overburden by shovel-and-truck operations using the largest power shovels and haul trucks in the world. The overburden is comprised of water-laden muskeg (peat bog) on top of clay and barren sand with a CBR of <1%. The oil sands are typically 40-60 meters deep, on top of limestone rock, which are excavated and hauled to a central processing facility.

When the frozen ground thaws in the spring, the saturated water of the muskeg peat causes severe swelling and heaving of road structures. With the return of winter, the freezing of the high water tables buckle and distort road surfaces.

Suncor needed to reinforce the access and haul roads used by the huge CAT haul trucks (600+ ton GMW – Gross Machine Operating Weight) to the processing facility. The solution had to provide durable performance for extreme loading in the softest subgrade. In addition the solution had to maintain dimensional stability in -40°C temperatures as well as through cold-hot thermal cycling.

Conventional Approach

Construction in muskeg-laden areas often requires the complete removal of the soil and replacement with gravel. If the muskeg is not completely cleared to bedrock, its high water content will cause buckling and distortion from winter freezing, much like permafrost. Log (corduroy) roads and tree mulch waste infill are typically used for haul roads by forestry and other resource extraction industries. However, they cannot support heavy loads and /or sustained use. Temporary wooden or steel mats are used to create mattresses across the soft terrain; however these are best for small areas – they are expensive, logistics are complicated and time-consuming to install.

Neoloy Geocell Solution

Neoloy Geocell-356-150 was implemented in the base layer to reinforce the subgrade and increase the oil sands’ bearing capacity. The reclaimed sand from the bitumen processing was used for cell infill (15 cm + 3 cm overfill), with a 15 cm stone wearing course on top.

The high tensile stiffness and strength of the Neoloy enhanced the engineering value of reclaimed sand under heavy loading soil. Neoloy Geocell performs well even over fully saturated conditions. In addition Neoloy’s very low coefficient of thermal expansion (CTE) – particularly when compared to HDPE geocells – provides long-term dimensional stability even under the subarctic freeze-thaw cycles.

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