Geotextiles & Geocomposites
Traditionally, trackbed renovation has involved the use of granular materials to improve bearing capacity, protect a moisture sensitive subgrade and separate ballast from underlying fine grained soils. While granular treatments were very effective, installing them required long possessions which were expensive and typically only relatively short in length.
Since the early 90’s, geosynthetic engineering has evolved to replace almost all of the functions of the granular material below the ballast. This has greatly reduced the time and cost involved in completing a track renewal by speeding up installation times and increasing productivity.
Aqua’s full range of products incorporate the four Network Rail specific product groupings, ‘Separator’, ‘Robust Separator’, ‘Anti-pumping Geocomposite’ and ‘Geogrid and Geocells’ as well as providing hybrid solutions, combining multiple products for increased benefits versus a traditional multi-layered approach.
Formation Treatment Definitions
As defined by Network Rail Standard NR/L2/TRK/4239 the following terminology is used to describe the various types of Geotextile & Geocomposite products that are available:
Geotextile Separators
Aqua Terratex® geotextile separator is a non-woven needle punched product designed to separate the sand or soil layer from the ballast.
Terratex 4050 and Terratex 70 offer enhanced abrasion and puncture resistance properties when compared to a heat-bonded separator.
“Permeable geosynthetic used to prevent intermixing between blanket materials and the ballast.”
Robust Separators
TED 2® has been the standard robust separator for rail applications since 2003. TED 10® is a more recent addition to this particular type of geosynthetic. These should be used when the particle size of the
formation contains a significant amount which is greater than 14mm.
“Heavy duty geotextile/ geocomposite used to separate ballast and a course grained formation materials.”
Anti-Pumping Geocomposite
This type of geocomposite was developed to replace the need to install a sand blanket on “wet bed’s” and sites where there is a high proportion of clay soils and water present.
When train’s pass over such areas the clay can be pumped into the ballast under hydrostatic pressure causing ballast slippage and deterioration to the track quality. Tracktex® allows the water in the formation to pass through its unique micro-porous core whilst preventing small clay fines from passing.
This product can be used as a standard solution no.3.
“Geosynthetic material which can be used as an alternative to a sand blanket dependent on existing drainage and formation/ sub-grade condition.”
Formation Reinforcement
Used to help stiffen the track especially in areas of soft ground. This stiffness increases the life span of the rail and train components whilst also reducing the maintenance time regime. These can also be used with geotextiles to further enhance the formation.
“Plastic mesh with high tensile stiffness and used as reinforcement at the base of a ballast layer or, within the ballast layer itself.”
“Expandable honeycomb structure which is filled with granular material to create a more resilient formation layer that can better distribute the stresses, generated by traffic, on the subgrade.”
Aqua Geoweb is the only system that meets the Network Rail standard for joint strength due to the patented method of connecting adjoining panels.
Combination Geocomposites
These materials provide a versatile solution to problematic areas. In the case of TED 4, by combining a separator with a grid the product provides filtration and separation combined with ballast reinforcement, therefore helping to stiffen the trackbed.
Another advantage, over separate rolls, is their ease of installation due to the lengths of the products involved. Being 25m long it is much easier to align the product to the track than separate 50m long rolls.
Contaminated Ground Impermeable Membrane
Designed specifically to prevent contamination mixing with ground or surface water, these type of product is not typically suitable for use under the track except in exceptional, specific circumstances.
Track Access Systems
For quickly and easily gaining access to the track or dig site, this range of products represent a revolutionary, lightweight yet durable range of access products.
