TERRAM Geosynthetics are used extensively in the construction of highways in civil engineering applications  - from preventing intermixing of sub-base and subgrade layers, control erosion on cut slopes, for roadside drainage, as part of SUDS projects for infrastructure access and in the construction of retaining walls, bridge abutments and steep slopes.

Improving granular layer performance

TERRAM Standard geotextiles is used to prevent the intermixing of sub-base and sub-grade layers. 

Without the use of geotextiles, 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 by filling the ruts but even this can be uneconomic or unacceptable if stone has to imported over long distances at a later date.

However, in paved road situations the intermixing can manifest itself as deformation at the pavement surface e.g. cracking and/or rutting, by which time the damage at the sub-base/subgrade interface cannot be repaired without re-construction and any repairs are cosmetic rather than structural. 

Site-damage resistance

A geotextile is most susceptible to damage during installation, as opposed to during service life, therefore it must be capable of withstanding the rigours during this period.

If a geotextile is of insufficient quality, and is liable to tearing or being punctured, then the product is incapable of performing its intended design function. 

The filaments of many low-cost, woven textiles can easily be teased apart, even during physical examination. With little integrity it is easy to imagine how these products might perform when angular stone is placed on them and compacted. A textile filter/separator must have an apparent pore size which remains unaffected by loading. Any openings which are created or widened, or are caused by tearing/puncture, will allow subgrade particles to be pumped through to the sub-base.

Radial load requires isotropic properties

Wheel loading at the sub-base/subgrade interface is radial. This means that the geotextile requires isotropic strength to deal with this action. It is not sufficient for the textile to have high strength in one or two directions, as is evident with woven products.

Sustained filtration

Geotextiles must provide sustained filtration, to allow the free passage of ground water, whilst also separating the two layers to limit the passage of soil particles, which involves matching the geotextile pore size with the sub-grade’s smallest particle size. 

This does not mean that the geotextile should have a pore size smaller than the smallest soil particle. It has been established that a geotextile acts as filter by virtue of a natural filter that is formed against the surface of the textile.

The ultimate objective is to maintain the integrity of the granular layer and thus gain the maximum life from the structure. This can be achieved by allowing its maximum bearing strength to be mobilised throughout the road’s width and depth, and throughout its life.

Typical applications where geotextiles are used in paved and unpaved areas beneath granular layers include:

• Highways
• Car parks
• Hardstandings
• Access and haul roads
• Cycle ways and footpaths

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TERRAM geotextile filter / separators prevent intermixing of granular layers
TERRAM standard geotextiles are used in highway projects
TERRAM geotextiles prevent sub-base and subgrade deformation


TERRAM Highways & Roads
TERRAM Railways
TERRAM geocomposites
B1 Drainage Geocomposite
1BZ Drainage Geocomposite
GEOCELL Slope stabilisation (M25 Widening)
GEOCELL & T1000 Erosion control for canal slope (Monmouth and Brecon Canal)
BODPAVE 85 Gravel-filled paver access / cycle route (Blackpool)
RG7 - Landfill Basal-cell-liner & side-slope protection/drainage (Beacon Hill LFS)
RG4, RG11 RG-SD19 Protection to Landfill basal & capping liners (Lean Quarry LFS)
RG25 & RG31 Liner protection for a deep landfill cell (Clifton Marsh LFS)
RG3 Landfill capping liner protection (Erin LFS)
RG4 & RG-SD19 Landfill cell side-wall drainage (Bryn Pica LFS)
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