In the design and execution of the vast majority of modern civil engineering and infrastructure projects, geogrids are key to the stabilisation of soil and ground. From highways to railways, from retaining walls to embankments, from the treatment of soft soils, to the choice of the right geogrid, the choice has an impact on both long term performance and the cost of construction.
Of the many choice on the market, two products are woven geogrid and warp knitted geogrid which will many clients, contractors and project engineers will need to compare prior to purchase. Whilst both ride to provide soil stabilisation and assist with load distribution, in manufacture, structure and materials and application, they’re very different! Knowing the contrast experience is beneficial to engineers when specifying the correct reinforcement solution for specific ground conditions and design spec, and to the purchaser in avoiding overspecifying or choosing a product not suited to the project in hand.
Here, in our words, are the key differences between woven geogrid and warp knitted geogrid.
What is a Woven Geogrid?
Woven geogrids are formed of high tenacity synthetic fibres which are woven, similarly to textiles weaving, together to form a grid of mutually perpendicular components. Polyester or polypropylene yarn or yarns within industrial yarn duties are typically used and are often subsequently coated with PVC, bitumen or similar material. The woven interlocking nature of the longitudinal and transverse of the two types of yarn means that woven geogrids are used on projects with a high load-bearing demand.Main Features of Woven Geogrid
- High tensile strength
- Low extension
- Low creep characteristics
- Good dimensional stability
- High strength interaction with soil and aggregates
- Suitable for long term reinforcement use
These geogrids find use for reinforcing retaining walls, stabilising embankments and improving soft ground.
What Is Warp Knitted Geogrid?
Warp knitted geogrid differs from the woven variety as it is manufactured using warp knitting instead of weaving. High-strength polyester yarns, or in some cases, fibreglass fibres, are stitched together. A protective coating of PVC or bitumen is then applied which also serves to increase durability.
Warp knitted geogrids have a more flexible structure. The process allows the fibres to maintain a high tensile strength and good adaptability to uneven ground surfaces. The grid is more adaptable to irregular surfaces. They are used for such applications as pavement and pavement overlays, slope stabilisation, road building etc.
Main Features of Warp Knitted Geogrid Flexible - High tensile strength and little, if any, fatigue
- Good to excellent asphalting bonding performance
- Good to excellent in reducing reflective cracks in roads
- Easy to install during construction
- Environmentally friendly
Due the above benefits they are widely used for this type of project work.
Manufacturing Process Difference
Woven Geogrid Production
With a woven geogrid the production uses the textile process of weaving. The high-strength yarn is interlaced, both ‘horizontally’ and ‘vertically’.After weaving the roll to the desired width and other properties, it is treated with a coating etc. This treatment reinforces UV resistance, chemical resistance, and adds durability in harsh environments.
Utilizing interwoven fibers gives the woven geogrid a significant mechanical interlock with soil particles. For this reason, woven geogrids tend to perform better under heavy load.
Warp Knitted Geogrid Production
Warp knitted geogrids are produced using knitting machinery. Rather than interlacing the yarns together, the fibers are stitched to each other in parallel directions.
This allows a more flexible reinforcement material. It also decreases the concentration of stresses inside the grid.
The product is simply coated after it has been knitted to give it more protection and a measure of dimensional stability.
This difference in how the two geogrids are produced partly accounts for the difference of behaviour of woven geogrid and warp knitted geogrids in engineering projects.
Structural Difference Between the Two
Woven geogrid Structure
Where a woven geogrid is a bit rigid, or at least, a more stable structure. Because the yarns are tightly inter woven together, the junctions are a strong constituent.
The potential strength of the tensile performance is excellent within a given amount of deformation from loading, which is also an advantage in reinforcing the base through confining the aggregates.Warp knitted geogrid structure
Warp knitted geogrids are not tightly woven together since the yarns are being stitched. The flexibility that geogrids offer are of great use in the handling and the installation on site.
In the reinforcement of asphalt, a flexible structure allows stress relief and prevention of the propagation of the cracks.
Material choice and coating
Woven geogrids are manufactured from:
Polyester (PET)
Polypropylene (PP)
High tenacity industrial yarns
and generally coated in:
PVC coating
Bitumen coating
Protective polymer type coating that helps extend the resistance to moisture, chemicals and the sun.
Warp knitted geogrids are usually produced from:
Polyester yarn
Fiberglass fibres
Basalt fibres
Fibre glass warp knitted geogrids are usually produced for asphalt pavement reinforcement as they need to be stable in heat and not elongate or stretch under use. Bitumen coated warp knitted geogrids are used in road overlay where dimensional stability is critical.
Although stiffness, has a use for use in retaining wall and embankment reinforcement.
Elongation
Woven geogrids tend to have lower elongation (deformed state while being subjected to tensile load).
Low elongation is critical in areas where long term stability of reinforced soil structures are important.
In warp knitted geogrid, they may bemore flexible, but still offer excellent properties.
Durability
Both their products in with proper coating offer good durability.Woven geogrid that’s also coated with PVC is an ideal candidate for earth reinforcements in long term projects; could be anywhere from fibreglass warp knitted being a great plus on its side on hot and cold temperature variations, etc. and durability against ageing from asphalt etc. Application Difference We look rounds at geogrids usage; Woven geogrid: All sorts soil reinforcement (soft soil etc.) and Reinforced Soil Structure (RSS) type of construction. Mainly opting for tougher retaining wall structures and embankment etc. that makes projects last long and so. Whereas on tougher workings and if we want it long lasting projects, we look to the woven geogrids. Warp Knitted geogrid: If we want it for asphalt pavements and overlay systems, crack prevention project types and quite prefer them, in airport pavements too actually, etc. Application and Construction Considerations Woven geogrid application must be strictly properly tensioned. Must be kept “flat”; during placement and aggregate-compression etc. Because that’s stiff and so demands real care in handling too. Warp knitted geogrid type, is also more convenient with carrying baselayers asphalt; that’s actually used for tacking coat (bond with a tack coat), appropriately. By structure it is somewhat flexible and that’s why usually quite easy to handle/ install. Cost Considerations It foreboils having to do with costs. Woven geogrid is sometimes more expensive (overtly at purchase) but for projects with cost savings on maintenance prone aspects, can be more reliable actually. Work is reduced regards. Inwardly, the WarpGeogrid is cheaper mostly and cost effective for most external workings. How do you Choose the Right? It boils down to applications if you’re to choose between one or the other; Ask your engineer for best result, compliance and precise working—say about load, soil, design life, and then the quite cost. There are other slightening differences if you look carefully, yet work with experts now. Conclusion, Though the similarity looks quite pronounced, but both woven geogrid and warp knitted geogrid are two materials worth accurately knowing well in this geotechnical domain.