Road & Highways Solutions - Terram

1 & Highways Solutions3 Geosynthetics have been used in civil engineering since the 1970 of the earliest applications was in the construction of highwayswhere simple geotextile separators were placed between the sub-baseand the subgrade to maintain the integrity of the stone in Highwaysand Related ApplicationsTERRAM has been themost-frequently-specifiedgeotextile in the UK for over40 products and manufacturing capabilityPart of the Berry Global Inc, Terram manufactures geotextiles, geocells and geocomposites along with other related materials such geonets, porous pavers and grass protection meshes that are proven and trusted throughout the UK and Terram team provides a unique range of value engineered Solutions for the construction of Highways , railways, landfills,pipelines, coastal/ waterways defences and in unrivalled expertise and experience in geosynthetics,accumulated over a 40 year period since the first Terram products were launched, Terram remains committedto the development of innovative and cost-effectivegeosynthetic - The Product The ability of a geotextile to allow the passage of water yet stillprevent intermixing of stone and soil has meant these filter/separators are being used every day around the globe.

2 At one end of the scale it could be a remote unpaved haul road or, at the other, a major highway connecting international business uses and products have expanded over the years astechnologists and engineers have innovated and exploited theunique properties of the products that have been developed are now being used to control erosion on cut slopesas a result of road widening schemes, for roadside drainage, aspart of SUDS projects for infrastructure access and housing/retail/commercial developments, and in the construction of retainingwalls, bridge abutments and steep geotextile filter/ seperatorSubgradeGranular sub-baseA natural filter is established adjacent to the geotextile s of the sub-base and subgrade prevents the full load- bearing capacity of the stone layer being mobilised and leads to failure.

3 A suitable geotextile acts as a filter separator throughout the highway s life and acts to preserve the stone layer s Terram GeotextilesWith Terram GeotextilesTERRAM GeotextileTERRAM Standard Geotextiles prevent intermixing of sub-base and subgrade intermixing causes a loss in bearing strength, as the stone layer becomesprogressively contaminated, resulting in failure in the form of deformation. Thiscan be remedied if it s an unpaved area/road by filling the ruts but even this can beuneconomic or unacceptable if stone has to be imported over long distances at alater Granular Layer PerformanceIf it s a paved road then the intermixing could manifest itself asdeformation at the pavement surface cracking and/or rutting,by which time the damage at the sub-base/subgrade interfacecannot be repaired without re-construction and any repairs arecosmetic rather than structural.

4 It is therefore better to pre-emptthe problem by including a suitable ResistanceThe geotextile must first be capable of withstanding the rigours ofinstallation as this is when the textile is most susceptible todamage. If it is not sufficiently robust, and is capable of tearing orbeing punctured, then the product may be incapable of performingits design function. For example, the filaments of many low-cost,woven textiles can be easily teased apart, even during physicalexamination. They have little integrity and it is easy to imagine howthey will perform when angular stone is placed on them andcompacted. A textile filter/separator must have an apparent poresize which remains unaffected by loading. Any openings which arecreated or widened, or are caused by tearing/puncture, will allowsubgrade particles to be pumped through to the Load Requires Isotropic PropertiesThe loading from a wheel at the sub-base/subgrade interface is radialand this means that the geotextile should have isotropic strength todeal with it.

5 It is not sufficient for the textile to have high strength inone or two directions as with woven FiltrationThe geotextile must provide sustained filtration whilst also separatingthe two layers the textile must allow the free passage of groundwater yet limit the passage of soil particles. This involves matching thepore size with the sub-grade s smallest particle size. This does notmean that the geotextile should have a pore size smaller than thesmallest soil particle. It has been established that a geotextile helpscreate filtration by virtue of a natural filter that is formed against thesurface of the ultimate objective is to maintain the integrity of the granular layerand thus gain the maximum life from the structure. This can beachieved by allowing its maximum bearing strength to be mobilisedthroughout the road s width and depth, and throughout its paved and unpaved applications where geotextiles are usedbeneath granular layers include: Highways Car parks Hardstandings Access and haul roads Cycle ways and footpathsTERRAM Standard Geotextiles see page 175 Terram Data Sheets, Installation & Design Guidances andCase Studies can be downloaded from Data Sheets, Installation & Design Guidances andCase Studies can be downloaded from thickness (mm)Axle load (tonnes)302015155 Fig.

6 1 Example: Subgrade CBR = 2%, Axle load = 10 tonnes, Stone thickness required = CBR (%)Soil type Plastic index % >600mm <600mmHeavy clay 70 2 1 60 2 50 2 40 3 2 Silty clay 30 5 3 Sandy clay 20 6 4 10 7 5 Silt 2 1 Sand

7 (poorly-graded) non-plastic 20 10 Sand (well-graded) non-plastic 40 15 Sandy gravel (well-graded) non-plastic 60 20 CBR% Depth of water table below formation levelFig. 2 Some approximate CBR values for soils at their natural moisture contentSubgrade CBR value (%)T4000T3000 Maximum stone size (mm) 3 Geotextile Selection7 The thickness of a sub-base and/or capping layer should be determined usingappropriate national design criteria. Other more simplified procedures may beadopted if these do not exist or are example, the nomogram shown is for the design of unpavedroads and may be used to check initial layer thicknesses for apaved road, see Fig. information is scarce, the following may prove useful for theselection and installation of the most appropriate Terram guidelines should not be used to replace more rigorous designand the experience of contractors familiar with the installation Strength and Moisture ContentThe selection of the most appropriate Terram grade is largelydependent on the strength and moisture content of the should be used to assess these parameters.

8 Fig. 2 may be used for guidance in the absence of field SelectionThe Terram grade must be sufficiently robust to resist installationdamage. The lower the subgrade strength and the larger the stone,the more robust the grade needs to area should be cleared of any large objects, such as stonesand tree stumps, before geotextile placement. Ruts and sharpundulations in excess of 100mm should be filled and perennial weeds, such as thistles, should be treated withweed killer. Other vegetation can be left undisturbed, if this isallowable and not detrimental to the structure. The presence ofsurface vegetation can actually aid construction with very soft CBR <l% and un-drained shear strengths <10 geotextiles can be unrolled directly onto a subgrade withadjacent and subsequent rolls overlapped between 300mm and1000mm - the softer the subgrade, the greater the combination of overlapping and sewing may be more economicalwhere the subgrade strength is particularly low, or in other and plant must not run directly on exposed traffic should be restricted to areas of textile whichhave been covered with sub-base and preferably compacted tothe minimum required Selection and PlacementThe sub-base must be well-graded, compactable and forpermanent works, capable of transporting rising water andresistant to long-term degradation.

9 Recommended grading bandsfor compactable granular materials are shown in Fig. sub-base thickness will depend on loading and on the strengthof the subgrade. The thickness should take into account themaximum anticipated axle load, both during construction and inservice, and should be increased by 10-20% on bends or where aslightly inferior sub-base is should be bladed forward over the textile and gradeddown to the required un-compacted depth. Typical practice with afirm subgrade is to place the sub-base in layers which arecompacted to 150mm using a a soft subgrade it is prudent to place at least 300mm oflightly-compacted sub-base in one lift (500mm on an exceptionallysoft subgrade) before overlaying this with a thinner layer ofbetter-compacted very low-CBR subgrade, heavier traffic loadings, or a poorly-gradedsub-base may require differing techniques.

10 For example, heavycompaction with a very soft clay subgrade can lead to rutting andheave, and it may be necessary to increase the initial layer thicknessand allow time for consolidation of the subgrade before theplacement of thinner layers and applying more intense Standard Geotextiles see page 17 Terram Data Sheets, Installation & Design Guidances andCase Studies can be downloaded from and embankments. The drainage function is a critical element in the design of soil slopes and in slip , easy to handle, efficient and cost effective drainage systems are necessary in areas of construction such as basements, culverts, car parks, reservoirs and many other structural and subsurface edge drains running parallel to a roadway are necessary to intercept the lateral flow of groundwater.