Geocomposite Material for Civil Engineering Applications
Geocomposites are combinations of different geosynthetic materials for civil engineering applications that perform multiple functions including separation, reinforcement, filtration, drainage, and containment. They offer enhanced performance and improved construction outcomes compared with traditional construction materials.
Drainage
Reinforcement
Geocomposites combine a nonwoven with a geogrid to add separation, drainage, and reinforcement functions. They provide high tensile strength with good in-plane permeability for cohesive soils. This combination of function allows for the maximum use of space within a design while providing adequate stability and retaining capacity.
Mechanical damage induced by repeated loading or abrasion is one of the most important agents that may induce undesirable changes in the behaviour of geosynthetics. The present work complemented previous research by submitting a geocomposite (a polypropylene nonwoven geotextile reinforced with Geocomposite materia polyethylene terephthalate filaments) to degradation tests in which it was subjected to both repeated load and abrasion. The impact of these degradation tests was measured by monitoring changes in the tensile and tearing behaviour of the geocomposite.
The results shown in Figure 1 indicate that, for the abrasion test, changing the side of the geocomposite facing the load application mechanism had no marked influence on the degradation suffered by the specimens. However, for the tensile test, there was a clear difference between the samples tested in the MD and those tested in the CMD. This was because the MD filaments were arranged in thicker sets and therefore more resistant to damage than those in the CMD.
This result suggests that, for geocomposites with different structures on both sides and directions, the standard abrasion test must be modified in order to take into account the fact that the differences in structure on the two test surfaces are likely to have an impact on the resulting degradation.
Filtration
Geocomposites have filtration and separation properties to prevent mixing of different soil layers, and they can help control soil erosion. They can also improve soil drainage and provide stability. Environmental protection is another important use for Geocomposite materials, and they are often used in landfill liners and caps.
Drainage
A major benefit of using a Geocomposite is its ability to act as a leachate drainage medium, replacing conventional aggregate. The permeability of the composite allows the waste material to flow through it, rather than accumulating around the drain pipes. The composite can also be designed to reduce the number of drain pipes required, which can save on installation and maintenance costs.
The filtration properties of the composite are achieved by the geotextile filter fabric and the polymer core. The polymer core is typically fluted for ease of water conductivity, and fashioned into a 4 in. (100 mm) wide stocking. The geotextile layer is then bonded to the base of the core to create a robust, permeable drainage blanket. Traditional sand drains have all but disappeared as a method for fast consolidation of fine-grained saturated soils since the development of this technology.
The geocomposite was tested for compliance with the required design and installation parameters prior to its gabion wire mesh suppliers incorporation into the site works. Detailed analysis of the results showed that the geocomposite was capable of handling the volume of leachate expected to be disposed from the landfill cell, and could be installed with minimal pumping.
Drainage
Drainage is essential to the stability of most geotechnical constructions. Geocomposite drainage products provide pathways for water to flow, preventing the buildup of excess moisture and maintaining the integrity of the construction.
Geocomposite drainage is usually formed by a plastic drainage core that provides a high flow path for liquids (typically water in civil engineering applications) bonded to one or both sides of nonwoven geotextiles which filter out soil particles and prevent soil intrusion (Figure 8.8). This allows the drainage system to be placed directly adjacent to a pavement section for lateral drainage out of and away from the roadway surface, eliminating the need for an additional underlying perforated drain pipe.
These systems are also commonly used as value engineered alternatives to sand drains for geoconsolidation and preconsolidation of soft soils where the drainage function is required during the consolidation process (see Chapter 9) and are very effective at reducing groundwater levels in road pavements. They are a very cost-effective solution to traditional granular drainage layers which must be laid at a greater depth and have the added advantage of requiring no aggregate backfill.
These drainage systems are also very useful in intercepting and conveying leachate and running vapor from landfills or for running vapor below pond liners of various types. Field trials were undertaken to establish the performance of these drainage geocomposites in their intended application. They were found to be a robust drainage system, with good capacity for filtration, biological clogging and long term hydraulic flow.
Containment
The containment function of Geocomposite materials serves to prevent liquids, gases and even soil particles from moving around a site. This is achieved by offering high levels of impermeability. This function is typically performed by geomembranes, although Geotextiles and liners can also be used.
Geocomposites with the containment function are often made with a biplanar geonet core which has two layers of ribs oriented at an angle to improve drainage. A non-woven needle-punched geotextile layer is then laminated on either one or both sides to prevent soil particles from clogging the drainage core. This is an innovative solution that has been successfully trialled at a landfill near Bury in the UK by Viridor Waste Management, Wardell Armstrong and Layfield.
Erosion Control
Geocomposites with the erosion control function are designed to stabilise slopes and riverbanks by preventing soil movement and allowing vegetation to establish. They are often prefabricated and factory assembled to save on installation costs and ensure the desired engineering outcomes are achieved.