Geotextile & Geogrid Technical
Physical Properties, Case Studies and Installation Guides
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Geotextiles are a geosynthetic material used for civil applications including drainage, soil reinforcement, separation of gravel and soil, environmental applications including de-watering of contaminated liquids, geomembrane protection.
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Nonwoven polypropylene (PP) geotextiles are made from needle punched polypropylene staple fibre. These fibers are cut, opened, laid onto a web, needle punched, inspected, tested and rolled. The production technique produces a product described typically as “a nonwoven needle punched geotextile”.
Nonwoven polyester (PET) geotextiles are a strong 3 dimensional structure with excellent filtration. They also have a high melting point and UV resistance.
- Roadway Stabilisation/ separation. Roads and highways are built using geotextile to prevent aggregate from mixing with the subgrade and to strengthen the soil, reducing pot holes.
- Drainage. Nonwoven geotextiles are ideal for drainage applications. Unlike woven geotextiles (with the exception of monofilament drainage fabrics), polypropylene nonwovens resist clogging. Nonwovens are placed in direct contact with the earth where drainage stone, perforated drain coil, etc may be placed. The nonwoven filters soil and waste while allowing water and leachate to pass.
- Geomembrane Protection. Heavy weight nonwoven geotextiles will cushion and protect geomembranes from puncture caused by aggregate and basecourse. Gas Venting: Heavy weight nonwoven geotextiles are used for collection and lateral transmission of liquids and gases that may build up under a geomembrane used in a capping of waste facility.
- Hard Armour Underlay. Nonwoven geotextiles are recommended to help relieve hydrostatic pressure beneath hard armour and prevent soils from migrating to the surface providing an effective erosion control method.
Woven geotextiles are manufactured by extruding polypropylene film and then slitting the film into individual yarns which are then woven to form the geotextile.
These geotextiles perform several important functions. Where separation is required on firm soils (CBR ≥ 8 %) a woven geotextile provides a strong and economical solution. The grades of geotextiles used for this are typically 100 to 250 gsm. For applications where a weak subgrade needs to be reinforced (CBR ≤ 3 %) a high strength woven geotextile is used. These are classed by strength and are typically from 35 kN to 1000 kN.
- Unpaved Roads. Woven geotextiles provide a stable base for unpaved roads. The fabric prevents subsoil mixing with aggregate which, without geotextile, will quickly require repair. Not only will the soil migrate to the surface but also deep ruts will occur causing greater repair costs. Woven geotextiles also provide stabilisation over soft ground. Where access roads become boggy due to trucks and poor weather, a woven geotextile can provide the needed foundation by spreading the load across a wide area.
- Roadway Stabilisation/ Separation. Woven geotextile greatly strengthens paved roads. Roads were traditionally made by using extra aggregate which was designed to be absorbed by the soil. Over time the soil becomes weaker and potholes form. Syntex woven geotextile will provide a permanent separation barrier. Even with the constant flow of heavy truck traffic, a road with a Syntex woven geotextile will retain separation of aggregate and subgrade.
High Strength Woven Geotextile
High Strength woven geotextiles polypropylene (PP) are manufactured in grades from 35 kN to 105 kN and High Strength polyester (PET) from 150 kN to 1250kN. They have the advantage over conventional geotextiles in when they are subjected to load they can reach full tensile strength without undergoing the initial elongation associated with the straightening of the woven yarns. This allows immediate soil to geotextile load transfer.
These geotextiles provide excellent creep performance and high tensile modulus. They also provide maximum performance for weak subgrades and offer a combination of high filtration, high strength and separation. A high frictional surface between the basecourse and the road is created with a high strength at low strain resulting in low vertical deformation.
High strength woven geotextile has good filtration characteristics allowing for reductions in saturated fill and subgrades for soil reinforcement in applications including embankment stabilisation, steepened slopes, retaining walls, lagoon closures and landfill lining systems.
High strength geotextiles are also used for geotextile tubes which are used for the dewatering of contaminated materials, shoreline and coastal protection, artificial reefs, etc.
- Steepened Slopes. The geotextile is placed in layers between the soil to provide tensile strength to the slope and replace geogrids and earth anchors as a cost effective alternative by using existing fill, reducing the need to import rock.
- Retaining Walls. To maximise use of available land it is often necessary to build vertical retaining walls. The choice of materials can be a rigid cast-in-place concrete structure, pre-cast panels, modular blocks, etc. Syntex high strength geotextiles provide soil retention on face wrapped walls and slip resistance in backfill soils. They provide strength plus prevent erosion behind the wall.
- Earth Embankment. Construction over soft foundation soil (with a CBR of less than 1) the choices become restrictive due to excavation costs and time factors. Syntex high strength geotextiles were designed with this in mind. They provide a firm and permeable platform to strengthen the ground. This is a considerable cost saving solution to a common problem in construction. Syntex high strength vastly increases the tensile strengths of the soils, thus increasing the factor of safety to acceptable levels against sliding, lateral spreading, ground stability and bearing capacity failures.
The geotextile provides high strength and maintains separation from the granular fill above while allowing drainage.o maximise use of available land it is often necessary to build vertical retaining walls. Choice of materials can be a rigid cast-in-place concrete structure, pre-cast panels, modular blocks, etc. Syntex high strength geotextiles provide soil retention on face wrapped walls and slip resistance in backfill soils. They provide strength plus prevent erosion behind the wall.
- Landfills and Lagoon Closures. Due to difficulty in building new landfills the current practice is to construct new cells on top or next to existing closed landfills. High strength geotextiles allows the landfill capacity to be expanded by preserving the integrity of the new lining system. They reduce the differential settlement caused by biodegradation under the weight of the new waste. High strength wovens offer greater savings over double layers of uni-axial geogrids. Lagoons containing industrial wastes often close before settlement which require the installation of an impermeable cap over the thick wastes. High strength geotextile covers over the lagoon provides several advantages including separation, stabilisation and reinforcement, both of which aren’t adequately performed by geogrids alone.
High Strength geotextiles are manufactured into tubes for a range of applications including de-watering, artificial reefs, wetland reclamation and shoreline protection.
For de-watering applications geotextile tubes are filled with various materials including dredged wastes, contaminated soils, fine sludge and other hazardous wastes. The tube then acts as a huge filter and begins the process of de-watering. Woven yarns in the material slowly drain and retain contaminants. The final stage is consolidation of the waste which can be removed for disposal. Often the filtered water is of a high enough quality as to be returned to the source without further treatment.
A successful project will retain the contaminants and allow a high filtration rate with maximum consolidation. Our engineers can assist you in determining the type of contaminants and whether additives are needed to coagulate the waste. The whole process, once the tubes are setup and de-watering begins, is very straight forward with minimal costs. For very fine grain sludge further filtration can be achieved using both an inner and outer tube. The inner tube is a heavy grade nonwoven geotextile which is designed for retention of fines and the outer tube is a high strength woven polypropylene or polyester for strength.
- De-watering of Industrial Waste. Industrial waste from industries such as timber, mining, chemical, etc. geotextile tubes are a cost effective and environmentally friendly solution when compared to traditional methods of de-watering and disposing of solid waste. Contaminated sediments from collection ponds and creeks which have been polluted by industry, sewage overflow and storm water runoff can be successfully de-watered using geotextile tubes. Where a flocculating agent is used tests have indicated reduction of such contaminants as dioxin, lead, arsenic, etc. with a containment efficiency of over 99.8%.
- De-watering of Marine Sediments. A typical de-watering operation for a municipal sludge pond or lagoon allows for the continual filling of tubes with each tube taking approximately one hour to completely fill. The tube will typically rest in the de-watering trough and allow to solidify for a period from 1 to 3 months depending upon the type of material. Generally a reduction of more than 60% is achieved during this phase. The water which flows out is often suitable to be returned to the pond without further treatment with significant reductions in bacteria.
- De-watering of Agricultural Wastes. Geotextile tubes have proven to be a practical and cost effective solution to providing a method of de-watering and separating agricultural wastes. When left untreated or stored in ponds these wastes can create pollution to our rivers and lakes. The geotextile tube will effectively remove nutrients and separate solids from agricultural wastes. Once de-watered the solidified solids, including dried nutrients, can be used as fertiliser.
- Marine Structures and Coastal. Geotextile tubes are designed and manufactured to be fully submerged in a marine environment. This includes their use as breakwaters and artificial reefs. For these extremely demanding environments, survivability of the material is essential. The tube needs to be fully UV resistant with a high resistance to abrasion and tear. For these applications we can provide a series of tubes in layers which can be filled with dredged materials underwater with care taken during filling to ensure the structure does not move due to wave action. Geotextile tube containers are made to protect coastline and help prevent beach erosion. These tubes can be made in small units built as a wall against the impending forces of erosion. Ranging in size from 1 m to over 5 m high these high strength geotextiles offer maximum resistance to tear, abrasion and UV. Also available but less resistant to mechanical damage are economical heavy grade nonwovens. These nonwovens can provide a means for fast marine growth due to the porous nature of the material.
Geogrid is a geosynthetic material used to strengthen soil including subbase for roads and to reinforce retaining walls. The main feature of geogrids is their ability to allow soil to anchor to structures through the geogrids apertures and ribs.
- Roads, railways, ports and other paved areas
- Airport runways
- Temporary roads and other unpaved areas
- Slopes Reinforcement
- Environmental protection of slopes
- Landfill Sites