Creating a successful structure involves several stages. Each stage has some components without which the structure cannot be upstanding. To ensure a long-lasting and safe structure, engineers use one of the most crucial materials: geotextile sheets. These sheets act as a versatile protective shield and play various roles in creating a well-planned and well-designed structure. Before we get into it’s details, let’s first understand their definition and how they are used.
Definition of geotextile sheet
These are artificial, man-made geosynthetic sheets crafted from polypropylene or polyester. They are used conjointly with soil to provide proper support to the structure. These geosynthetic materials can be used as separators, filters, reinforcers and for drainage purposes. The history of geotextile sheets dates back to the 1950s when R.J. Barrett began utilising their advantages. Initially, these geosynthetic fibres were used as a substitute for coarse soil filters. Eventually, with time, Barrett started using them as precast concrete seawalls and other erosion control solutions. He explored these sheets in different kinds of fabric, defining key properties like Percent Open Area (the ratio of open space to the total area of the fabric, which affects filtration), often ranging between 6% and 30% in early designs. He also mentioned the required permeability and soil retention capabilities of geotextile sheets.
Types of geotextile sheets
It is true geotextile sheets are usually manufactured using materials like polypropylene or polyester. However, based on their application, they are of three types:
- Woven geotextile fibres: Woven geotextile fibres are manufactured by meshing together the fabric strips for more strength and stability. They are specially manufactured for handling heavy loads. Polypropylene is usually the material used for manufacturing woven geotextile fibres, as it can easily withstand heavy weights. Permeable woven geotextiles, typically made from polypropylene, are ideally used for separation and reinforcement applications where high tensile strength is required. The method for manufacturing woven geotextile sheets is weaving, using materials like slit-film tapes, monofilament, or multifilament yarns. Although these fabric sheets look like plastic, the woven texture is visible only at close inspection.
- Non-woven geotextile fibres: Non-woven geotextiles are usually manufactured using two materials: continuous filament yarn and short-staple fibres. Thermal, mechanical, or chemical techniques bond the fibres together to enhance their strength. If the sheets are manufactured using mechanical or thermal techniques, their thickness should be between 0.5 and 1mm. If the sheets are bonded using a chemical technique, the ideal thickness is up to 3mm. Non-woven sheets can be used in different ways, such as separation, filtration, and protection against seismic movements. For high-tensile, heavy-load reinforcement applications (like under railways and runways), high-strength woven geotextiles or geogrids are often preferred due to their lower elongation and higher strength. Non-woven geotextiles are essential in these projects for separation and filtration, but not typically as the primary reinforcement element for heavy loads. In applications like lining groundwater tanks, non-woven geotextiles are used as a robust protection layer to prevent the primary impermeable liner (geomembrane) from being punctured.
- Knitted geotextile fibres: Knitted geotextile materials are manufactured by intertwining a loop series of yarn. The knitting technique is used to make this geosynthetic material. The primary manufacturing technique for this geosynthetic material is knitting. The strength and durability of knitted geotextiles are tailored for specific applications, but it is not accurate to say they are universally stronger than all woven or non-woven types. High-strength woven geotextiles, for example, are specifically designed for maximum tensile strength in reinforcement. Knitted geotextiles are one category of geosynthetics. Other distinct categories include geogrids, geonets, geocells, and geocomposites, each with unique structures and functions.
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Usage of geotextile sheet
Geotextile sheets have several applications, as listed below:
- They play an excellent role as a separator. They can be installed between various soil materials. These sheets prevent the two different soil textures from getting mixed, allowing the soil to have the desired characteristics. This process is called separation.
- Geotextile sheets are also incredible filters. Engineers use these sheets to allow water to easily pass through the soil layers. This enhances the drainage process and prevents the coarse soil grains from passing through soil layers. These sheets can be installed horizontally and vertically, depending upon its applicability.
- These sheets are installed in geotechnical projects considering some factors that can contribute to soil improvement. These factors can include movement resistance, load support, and changes in bearing failure. Geotextile sheets reinforce the weak and moist subgrade and enhance the strength to support heavy-load infrastructure.
- While standard geotextiles are permeable, they can be used to create a moisture barrier when impregnated with a binder like asphalt. This composite system is used in applications like road paving to prevent water intrusion into the base layers. In applications like road paving, this composite system prevents surface water intrusion into the road’s base and subgrade layers, preserving their structural integrity.
Advantages of geotextile sheets
- Geotextile sheets are light in weight and, therefore, are easy to install.
- Since they weigh less, they cost less when it comes to transportation.
- They have higher tensile strength, more durability and less maintenance.
- They are permeable and act as excellent filters and drainage conduits, allowing water to pass through in a controlled manner while preventing soil particle migration. This helps manage water around foundations and prevent hydrostatic pressure buildup.
- It also enhances the soil characteristics such as strength, load-bearing capacity and friction resistance.
Disadvantages of not using geotextile sheets
- Soil erosion can occur more rapidly, leading to the loss of fertile topsoil and compromising the stability of structures built on or near the soil.
- Poor Drainage: Inadequate drainage can result in water pooling around foundations, leading to water damage, flooding, and potential structural issues over time.
- Soil may be more prone to settling, shifting, or sliding, which can affect the integrity of roads, embankments, and retaining walls.
- Structures may require more frequent maintenance and repair, leading to higher costs over the long term.
Geosynthetic sheets or materials are a new-age technology for building a durable and safe structure. These sheets play a vital role in providing a robust foundation that is water-resistant, has higher tensile strength, and is friction-resistant.