Causeway Design with PRS Neoloy Geocells, Proc. of Design and Practice of Geosynthetic-Reinforced Soil Structures, Pokharel, et al. (2013)

The paper discusses the design, construction and performance of a PRS-Neoloy reinforced causeway in Alberta, Canada for oversized trucks over very weak Muskeg.

Summary

Oversized load-carrying trucks (260 tons) in Alberta, Canada had to traverse a section of very weak and saturated subgrade, with the water table at the surface, with good quality road construction materials typically hard to find or very costly. Therefore a 200m x 6.5m causeway was constructed utilizing dual layers of NPA Geocell Reinforcement. The design was based on the Han and Giroud method, calibrated by tests at the University of Kansas and Kansas State University. Over a three-month period, heavy construction and drilling equipment, plus construction materials were hauled over the causeway, which remained in excellent condition. By comparison, unreinforced sections either side of the causeway failed during the same period.

Challenge – Weak subgrade, heavy vehicles

The oil sand region of Alberta is rich in hydrocarbons, but lies on very weak muskeg soil. This is especially problematic during the Spring thaw. Constructing sustainable roads for drilling projects in Alberta, which can withstand heavy vehicles usually requires hard to find and expensive materials.

Situated in the Algar Lake area, additional challenges included the water table sitting close to the existing ground level, threatening seeping into the causeway. Also, the road surface required lowering, due to a 144kV power line infringing on the required 10m clearance above.

Solution – Two layers of NPA Geocells

Following excavation, a geomembrane was inserted on top of the muskeg soil, followed by thick clay liner. Two layers of Neoloy Geocells were placed on top. The lower layer, compacted to 95%, was used as a construction layer for heavy construction equipment. The upper layer was compacted to 98%. The Neoloy Geocells had a creep reduction factor of 2.7kN/m over 50 years and long-term resistance to plastic deformation of 8.0kN/m over 50 years.

The design method was based on the method proposed by Han and Giroud, which was calibrated for Neoloy Geocells using static and cyclic plate-loading tests, plus full-scale moving wheel load tests at laboratories of the University of Kansas and Kansas State University.

Results – Excellent performance

The new causeway was monitored visually over a period of 3 months following construction. This period included the Spring thaw, which had previously proven particularly problematic. By May 2012 at the end of this period, rut depth was measured as less than 25mm and the causeway exhibited no signs of surficial failure. Having withstood 3 months of traffic including heavy construction equipment, drilling equipment and construction materials, the causeway was assessed to be in excellent condition.

By comparison, the roads connecting to each end of the causeway, which were unreinforced, were assessed to have failed by the end of May 2012.

Benefits – Stronger pavement, longer life cycle, less maintenance

Neoloy Geocells proved to be a reliable and practical solution for pavement construction on particularly weak soil in Alberta, Canada, bringing the following benefits:

  • Stronger pavement with a longer life cycle
  • Less maintenance required, reduced maintenance costs
  • More efficient transport of heavy vehicles

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