Industry Sector & Application:
Soil Reinforcement & Stabilization
In this application, the Canadian National Railway (CN Rail) wanted to build an additional 6-track extension at the Transcona Yard in Winnipeg, Manitoba. Heavy rail cars were expected to pass over this extension area and CN Rail was looking for an economical, efficient, environmentally friendly, and technically sound solution for their track extension. Soil conditions and properties were important considerations in the design of this project, as the site had swampy conditions with wet and soft clay soils.
Titan proposed a geosynthetics solution which incorporated a bi-axial geogrid composite using the Swamp Grid™. This created a stable formation on the weak subgrades to serve as a satisfactory foundation for the rail tracks trafficked by heavy rail cars. CN Rail was able to avoid costly conventional alternative methods by utilizing superior product supply and technical guidance from Titan.
Addressing Poor Site Conditions
Wet, saturated site conditions were the main challenge CN Rail faced during this project. When standing on the ground one would easily sink a minimum of 6 inches due to the low shear strength of the subgrade soils. Since it was not possible to place a capping layer on these soils, CN Rail was forced to delay construction of the track extension, which was further complicated by continuous heavy rainfall.
Further, a railway track constructed over soft and plastic subgrade soils may experience progressive shear failure and excessive plastic deformation. This would require frequent maintenance while disrupting operations, reducing efficiency, and increasing cost. The challenge was to design and construct a stable formation on the weak subgrades which could serve as a satisfactory foundation for the rail tracks trafficked by heavy rail cars.
Comparing Stabilization Methods for a Rail Track Extension
The Conventional Solution
Conventional solutions for soft soil stabilization include techniques such as:
- Excavation and replacement
- Lime or lime cement stabilization
- Vertical drains
- Sand or sand-lime piles
- Stone columns
These are cumbersome and expensive. In some cases, a working platform may be needed to allow the construction plant and equipment to move around. Due to these constraints and the cost involved, these solutions were not considered appropriate for this site.
Titan’s Geogrid Solution
Titan Environmental proposed a geosynthetics solution as the most suitable for this project. Based on the nature of the subgrade soils and the type of loading, the geosynthetic needed to do three things:
Titan’s Swamp Grid™ biaxial composite was accepted as the optimal solution for the site and was approved by the project’s design engineer. The installation was executed successfully, and the product performed very well.
What is Swamp Grid™?
The Swamp Grid™ biaxial composite consists of Pyramid Grid™ bonded to a 6oz continuous filament, needle-punched nonwoven geotextile. In this application, it was placed directly over the weak and saturated sub-grade and a 600 mm thick granular (< 50 mm limestone) capping/sub-ballast layer was placed and compacted above it.
How did Swamp Grid™ perform in this rail track extension?
- The apertures provided a high degree of interlock with the granular material.
- The positive mechanical interlock of the geogrid component with the fill particles created a laterally and flexural stiff platform.
- The product layer with the first lift of fill acted as a firm working platform facilitating speedy construction.
- The non-woven component acted as a separator, preventing loss of granular material into the soft subgrade during placement and compaction of the fill.
- The confinement provided allowed the capping layer to be compacted to high density.
- The reinforced granular foundation distributed heavy dynamic loads evenly/widely and provided a high degree of lateral restraint.
- This enabled the weak subgrade to resist the repeated loads of the rail cars without experiencing progressive shear failure and undergoing excessive plastic strains.
- The non-woven geotextile functioned as a filter to minimize the pumping of fines from the subgrade into the granular layer and prevented build-up of excess pore-pressures in the subgrade from repeated traffic loads.
Swamp Grid™ Specifications
Swamp Grid™ is an advanced combination product consisting of our EARTH GRID™ heat-bonded to a long-fiber PET nonwoven geotextile.
It is made of virgin polypropylene through a unique punching and drawing process, resulting in a bi-directional oriented monolithic and an isotropic bi-axial geogrid possessing integral nodes, high tensile and flexural stiffness, high torsional rigidity, and junction efficiency.
Designed as an all-in-one solution, Swamp Grid™ offers soil reinforcement with added soil filtration, soil separation, and sub-base drainage performance. This geogrid is extremely effective for stabilizing saturated soils that are susceptible to piping and preventing loss of imported granular material into the soft subgrade.
For more information on Swamp Grid™, CLICK HERE.
As we saw in this case study, site conditions can present unique design challenges. We know time is not always on your side and you could use help with a design solution. Titan works closely with project owners and consultants to evaluate site specific problems and help you choose the best geosynthetics solution for your project.
Our FREE pre-design service for geogrid applications provide first-class customized design support helping to save you time on infrastructure, site development and geotechnical projects.
Explore what Swamp Grid™ or any of our other geogrid soil reinforcement and stabilization products can do for you. Request a consultation using the form below.
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