Drainage Geonet
Drainage geonet is produced in a controlled factory setting, with strict manufacturing quality assurance to deliver a consistent drainage layer for erosion control, landfill leachate management, slope stabilization and gas venting applications.
The drainage core is often heat-bonded to a nonwoven needle-punched geotextile on one or both sides to prevent soil particles from clogging the geonet. These combined products are referred to as geocomposites.
High Load Capacity
The three-dimensional biplanar structure of the drainage geonet allows it to withstand large amounts of load without damaging or losing its shape. It can also be subjected to significant pressure without compromising its structural integrity or becoming damaged by vibrations or the impact of heavy vehicles and equipment.
Because of their high compression resistance, geonets can be used in a variety of applications. They are suitable for landfill cells and cover, roads and railway construction, slope stabilization and drainage systems.
Since the drainage geonets are prone to UV and heat exposure, it is recommended that they be covered in a protective layer or placed over a geomembrane or geotextile. The geonet should be adequately bonded to the covering material to prevent clogging. This bonding can be achieved by thermal fusing or with a nonwoven needle-punched geotextile. If a filter fabric is laminated on either one or both sides of the drainage geonet, it can retain soil and sand particles while still allowing filtered water to pass through to the drainage core. The resulting drainage geocomposite offers a cost effective and environmentally friendly solution for long term drainage design.
Flow Capacity
Drainage geocomposites consist of a three-dimensional bi-planar geonet with a non-woven needle-punched geotextile laminated to one or both sides. The geotextile acts to filter out soil particles that could clog the drainage Drainage geonet core. These are used to replace a granular drainage layer in landfill cells, road construction and other applications that require efficient lateral drainage of liquids or gases.
The long-term flow capacity of Drainage geocomposites has been tested under a variety of bedding conditions using a standard BAM test. This is done to ensure that the drainage geocomposites will remain functional over time and can sustain the loads they are under.
During installation, it is best to place the geonet rolls with their machine direction oriented up-and-down slope. This minimizes seams along the flow direction and allows for a continuous unbroken flow of drainage material. When seaming or connecting to other drainage components, plastic electrical ties or polymer braid are preferred. Any holes or tears in the geonet should be patched to extend a minimum distance beyond the edge and tied at minimum intervals.
Flow Rate
The in-plane transmissivity of a Drainage geocomposite, as measured by the flow rate of water flowing through it under a specified load, is a very important factor when selecting a drainage solution for landfill or containment applications. In contrast to gravel aggregates which are very bulky and difficult to transport, XPro geocomposites are light and easily moved around the jobsite in rolls, ready for installation with minimal labour and equipment.
Laboratory tests on multilinear drainage geocomposites show that their long-term transmissivity is not load sensitive. This is due to the ribbed structure of the geonet core which offers channelized flow and sustains compressive stresses. The geonet core also resists intrusion of soil in contact with it, minimizing the effect of backfill on transmissivity (Blond, Steinhauser and Fourmont 2017).
A simple to use online calculator can be used by engineers to provide an accurate transmissivity value for a specific project. The tool uses the GRI-GC8 methodology and requires reliable inputs to generate a good result. This enables site-specific requirements to be met while avoiding over-design.
Compression Resistance
Drainage geonets are crush proof and are designed to maintain their structural integrity under high loads, maintaining fluid and gas transmission. This characteristic makes them ideal for waste containment applications that require a heavy load bearing material such as landfill cells.
They are extruded in a multi-stage process that melts, mixes, filters and feeds the molten polymer directly into a counter-rotating die that imparts parallel sets of ribs into the preform. After the die, the ribs are bonded together through heat and pressure to form the finished geonet. The geonet is then water quenched, longitudinally cut in the machine direction and rolled onto a handling core.
Geonets can also be produced with a nonwoven needle-punched geotextile laminated to one or both sides of the drainage core to prevent soil particles from clogging the flow path. These are commonly PP plastic two-way geogrid referred to as drainage geocomposites and are manufactured with bi-planar or boxlike geonets. These products are usually placed with their roll direction oriented up the slope rather than across them because of their superior flow rate in the machine direction.
Durability
A Drainage geonet must be durable to withstand high loading conditions. This includes resistance to in-plane hydraulic flow rate (transmissivity), mechanical properties, endurance and environmental issues. These properties are typically tested via ASTM, ISO or GRI Standards.
In-plane hydraulic flow rate performance, including clogging, is an extremely important aspect of a geonet’s durability. In-plane hydraulic transmissivity is measured by a standard test procedure, and should be the primary criteria used to select a geonet for a particular application.
The manufacturing process of a Drainage geonet typically involves extruding polyethylene from a continuous melt line to form a three dimensional bi-planar core, then laminating one or both sides of the geonet with nonwoven geotextiles. These products, which are often called “geocomposites” by the manufacturers, provide a light weight, factory controlled, low maintenance and environmentally friendly alternative to traditional drainage materials such as granular stones, gravel or sand.
Rolls of a Drainage geonet are typically shipped to the project site in protective wraps. The wrapping should be strong enough to protect the geonet from damage during handling and storage, but not so strong as to interfere with the shear strength of the interface between the geotextile and the geonet.