Roads & Highways

Geosynthetics in highways and related applications Geosynthetics have been used in civil engineering since the 1970’s. One of the earliest applications was in the construction of highways where simple geotextile filters were placed between the sub-base and the subgrade to maintain the integrity of the stone layer. The ability of a geotextile filter to allow the passage of water yet still prevent intermixing of stone and soil has meant these filter/separators are being used every day around the globe. At one end of the scale it could be a remote unpaved haul road or, at the other, a major highway...

Improving granular layer performance TERRAM Standard Geotextiles prevent intermixing of sub-base and subgrade layers. This intermixing causes a loss in bearing strength, as the stone layer becomes progressively contaminated, resulting in failure in the form of deformation. This can be remedied if it’s an unpaved area/road by filling the ruts but even this can be uneconomic or unacceptable if stone has to be imported over long distances at a later date. Without TERRAM Geotextiles With TERRAM Geotextiles If it’s a paved road then the intermixing could manifest itself as deformation at the pavement...

Radial load requires isotropic properties The loading from a wheel at the sub-base/ subgrade interface is radial and this means that the geotextile should have isotropic strength to deal with it. It is not sufficient for the textile to have high strength in one or two directions as with woven geotextiles. Sustained filtration The geotextile must provide sustained filtration whilst also separating the two layers i.e. the textile must allow the free passage of ground water yet limit the passage of soil particles. This involves matching the pore size with the sub-grade’s smallest particle size....

The thickness of a sub-base and/or capping layer should be determined using appropriate national design criteria. Other more simplified procedures may be adopted if these do not exist or are inappropriate. For example, the nomogram shown is for the design of unpaved roads and may be used to check initial layer thicknesses for a paved road, Where information is scarce, the following may prove useful for the selection and installation of the most appropriate TERRAM grade. These guidelines should not be used to replace more rigorous design and the experience of contractors familiar with the Subgrade...

Vehicles and plant must not run directly on exposed textile. Construction traffic should be restricted to areas of textile which have been covered with sub-base and preferably compacted to the minimum required depth. With a soft subgrade it is prudent to place at least 300mm of lightly-compacted sub-base in one lift (500mm on an exceptionally soft subgrade) before overlaying this with a thinner layer of better-compacted material. A very low-CBR subgrade, heavier traffic loadings, or a poorly-graded sub-base may require differing techniques. For example, heavy compaction with a very soft clay...

TERRAM Geocomposite Drains are manufactured by bonding a compression-resistant net core between two geotextile filters or between a geotextile and a geomembrane. The grade of net dictates the composite’s flow capacity. The filter/net/filter composites are used for general area drainage and are easy-to-install, factory-assured replacements for tradition stone installations. The filter/net/membrane composites are used to drain from one side only and provide a barrier to the other – a cut-off drain. Both types can be deployed vertically or horizontally. TERRAM Geocomposite Drains are preferred to...

Sustainable Urban Drainage Systems (SUDS) Paved areas and roof gardens require a light and versatile drainage system capable of a high in-plane flow. TERRAM Geocomposite Drains offer high flow rates, high compressive strength and good resistance to creep. Their use reduces manpower and minimizes the need for heavy materials making them ideal solutions for these applications. Traditional drainage applications TERRAM Standard Geotextiles and TERRAM Geocomposite Drains are used in traditional drainage methods including Fin, Lateral, French and SuDS drains. Quick, easy to handle, efficient and cost...

Preventing frost heave Frost heave is perhaps the most common cause of failure for pavements in cold climates. Preventing frost heave beneath highways Frost-susceptible soils typically have a significant silt/fine sand content which allows the capillary rise of water. This water can turn to ice lenses in winter and further water is drawn up from the water table to balance the capillary forces. This cycle ultimately leads to heave at the surface which causes pavement cracking and uplifting. This is further complicated as the upper ice thaws in winter. The volume of water held as ice is many times...

Preventing the capillary rise of salt water TERRAM Salt Barrier has been specially developed to replace the granular layer and reduce environmental impact. Preventing the capillary rise of salt water TERRAM Salt Barrier is similarly effective in preventing the capillary rise of salt water that would otherwise contaminate sweet soil layers capable of sustaining vegetation. This geocomposite can be used instead of the traditional 300mm thick stone layer which would have been used in the past. A much more environmental-friendly alternative, particular if stone is not locally available. TERRAM Salt...

Earth Reinforcement TERRAM Geocell provides a cost-effective alternative to conventional earth retention structures due to its flexibility and suitability for use with a wide range of infill materials and foundation soils. The system eliminates the potential for cracking, spalling, splintering or corrosion that can affect concrete, steel and timber based systems. It can be installed almost vertically to form an effective, economical earth retention structure. TERRAM Geocell is used in horizontal layers to form a wall structure. This can either be the panels themselves to form a gravity structure...