Whether for use in a new road or highway section, drainage ditch, railwaybed, retaining wall, or beautiful landscape, the structure depends to a large degree on proper separation of the soils. When at different times and in various places the unmistakable layers mix, that structure often collapses and all manner of bumpy ruts, settlements, poor drainage, and expensive upkeep ensues.
The answer often lies in Geotextile Fabric, which provides a stable, and still-permeable barrier between soil types, allowing the base materials to perform that duty longer.
This modern “magic curtain” is today employed by engineers when needed (and it’s needed often) as Non-woven Geotextile, Woven Geotextile, Needle-punched Geotextile and Heat-bonded Geotextile on infrastructure and civil engineering projects worldwide. The technology separates, filters, and drains soils, reinforces weak ground, and does so within reasonable additional construction cost.
This article explains separation, why it matters in construction and how to choose the right geotextile fabric for application in general terms.
What Is Soil Separation in Civil Engineering?
Soil separation is preventing gentle pressure from forcing different types of soil into a slurry, as if peanut butter were smeared between two slices of bread.
In many applications, a strong aggregate is placed over a weak subgrade soil. Without protection, tiny particles of the sub-grade pass between the aggregate particles over time, the aggregate squeezing them between. Correspondingly, aggregate particles in turn are forced into the weak sub-grade below.
The soil is forced together, so it cannot distribute load properly. Eventually the structure collapses.
Geotextile Fabric is the meat in the sandwich, keeping the bread apart while allowing water to move.Common separation uses include:
Road construction
Driveway stabilization
Railway subgrades
Landfills
Drainage systems
Embankments
Parking lots
Foundation for retaining walls
What happens when separation is not provided? The service life of the road much shorter!
How does geotextile fabric perform its task of Separation Layer? In a nutshell, by maintaining the integrity of each soil layer.
When geotextile is inserted between soft soil and aggregate subbase, it performs the following:
Namely, looking a barrier between the fine soil migrating upward.
This assists in maintaining aggregate base thickness and performance and consequently load bearing serviceability.
Aggregate sinks into low bearing flow weak subgrade soils and an appropriately selected Geotextile Woven or Non-woven Geotexticle distributes the stress more evenly stopping upward flow and reducing the degree of rutting.
Water is a quick destroyer of soil structures. Geotextile materials permit controlled flow of water from suited base thru the fabric back into the earth. Water can pass round but never through the soil particles themselves which together provide for separation and drainage.
Roads and driveways built without geotextile materials require much maintenance, and benefits from additional loads entered upon them. By preventing the contamination of body fabric, the service life is increased, and long term maintenance costs are reduced.
Types of Geotextile Fabrics Preferred—to comply with different site requirements “which” depend on soil conditions, anticipated traffic loads, drainage requirements and filtering agent in a host of applications. Usually produced by the processes of needle punching or heat bonding. Random fibres create a fabric with tremendous permeability and filtering characteristics. Benefits are:
- Great flow of water
- Good filtering characteristics
- Flexible to apply
- Very good puncture resistance
- Good subgrade support
Woven Geotextiles
Produced from woven polypropylene-propylene or polyester yarns. Compared to non-woven products, woven materials tend to have greater tensile strength at a much lower degree of elongation. The are suited to: - Road stabilisation
- Heavy load
- Soft soil reinforcement
- Driveway construction
- Embankment support
The separation is very good, and readily combined with a reinforcement action.
Needle-punched Geotextile
An undesirable manufacturing process, whereby thru’ the use of mechanical needles, form a hook and loop interlock of fibres together. This in turn creates a thicker, hardwearing laminate with great permeability. The benefits being: - Very strong filtering ability
- CBR Puncture Strength
- Conformable to rough surfaces
- Excellent Drainage
Heat bonded Geotextiles
Heat bonded geotextiles are manufactured by the process of thermal bonding. Fabrics are generally smoother, and having an accurately controlled opening size. More likely to be used for; their ecological properties and their general good UV resistance in an exposed outdoor environment - Fine filtering
- Lightweight separation
- Drainage protection
- Landscaping projects
Why Soil Separation Is Important in The Construction of Roads
One of the largescale applications of geotextile fabrics. Left to its own devices, over time, the aggregate base loses its efficiency. reduce drainage and weaken the structural layer.
Improving Load Distribution
Geotextiles help to spread the traffic loads over a wider area, reducing the pressure on weaker subgrade soils. The Roads become inherently more stable under repeated movement.
Reducing Rutting and Settlement
The softer the soil, the worse the rutting. When aggregates mix with soft, subgrade soils a properly installed PP Geotextile or PET Geotextile fabric will prevent aggregates disturbing the subgrade, helping to maintain the correct thickness of surfacing material and a smoother surface.
Longer Life for the Pavement
Most road failures start below the surface. By providing a proper base with the help of geotextile fabric the life of the pavement is extended and the need for reconstruction into the bargain. This is of particular value on highways and industrial yards subjected to heavy traffic.
Driveway Fabric Applications
Driveway stabilization is another application for geotextile separation systems. Soft soil conditions often cause gravel driveways to sink, deform, or even to develop potholes. Driveway Fabric provides a more solid base under the aggregate.
Preventing Gravel Loss When gravel is not separated from the more unstable earth, it too readily sinks into the soil and may soon become viciously loose. Geotextile fabric enables the gravel to separate more effectively and maintains a sharper line of demarcation that assists in keeping the surface quiet for longer.
Improving Drainage As in the case of pavement, if water collects, performance is impaired. Permeable geotextile allows water to straddle the material and flow (without causing failure of the earth) so that roads perform better in wet weather. - Lowering Aggregate Requirements
Because the aggregate layer remains cleaner and more stable, frequent replenishment is typically not needed.
This reduces both material and maintenance costs. - Importance of Permeability and Flow Rate
Permeability / Flow Rate is one of the most vital geotextile performance indicators.
A good separation fabric must permit the movement of water without sacrificing its ability to retain soil.
Permeability too low, water pressure builds beneath the structure that could eventually weaken and erode the soil.
Permeability too high, excessive soil migration may occur.
This is why so much care is taken in the balancing of filtration and drainage properties in product selection.
Compromising factors are:
Fiber structure
Fabric thickness
Apparent opening size
Method of manufacture
Soil particle size
Continuous Filament Geotextile products offer stable hydraulic performance due to the uniformity of the filament arrangement. - The Role of Tensile Strength and CBR Puncture Strength
Mechanical strength is another sine qua non.
Tensile Strength
Tensile Strength is each fabric’s resistance to pulling apart.
More resistance is a better thing for applications involving:
Heavy traffic loads
Weak subgrades
Coarse aggregate materials
Stress from construction
Woven geotextiles facilitate the best tensile performance. - CBR Puncture Strength
The CBR Puncture Strength is an indicator of the fabric’s resistance to puncture by concentrated loads.
This property is especially critical during installation. Typical separation aggregates contain sharp particles that could damage the material. Having a higher material puncture resistance helps keep an effective separation over the long term. - PP Geotextiles vs. PET Geotextiles
Both types of geotextiles are prevalent in construction and civil engineering projects but have their own respective advantages.
PP. (Polypropylene) geotextile fabrics provide almost a non-existent moisture absorption, great chemical resistance, fairly good flexibility and strong wet strength durability. Dealing with drainage projects and roadways, this is not a surprising material to find used.
PET. (Polyester).
When compared to PP materials, these offer a higher modulus of tensile strength. In addition to this they have good creep resistance, are quite strong with regard to dimensional stability and have impressive long-term reinforcement properties.
UV Resistant Geotextile Fabrics for Outdoor Related Projects
We often see geotextiles exposed to sunlight as a result of either installation or extended use. Manufacturing ‘UV Resistant Geotextile’ products is one way to help lessen the degrading effects of ultraviolet light. UV stabilization is a consideration in the erosion control sphere but also for:
Coastal protection and land stabilisation work;
Landscaping;
Temporary exposure during construction;
Agricultural use;
and more.
High-quality UV-resistant fabrics maintain at strength and filtration longer compared to low-grade UV fabrics.
Common Sectors or Industries that use Geotextile Separation Systems
Where do we find geotextile technology used?
Highway construction;
Railway engineering;
Mining;
Landfill;
Coastal protection;
Agriculture;
Drainage;
Retaining walls;
Sports fields; and similar;
Industrial yards.
How to Choose the Proper Geotextile Fabric
Numerous conditions require assessment before fabric geomaterials can be deemed suitable. These include:
Soil Types;
The requirements of fine earth differ from coarser materials in respect to filtration performance capability. The use of particle size distribution tables is critical;
Load Conditions;
With heavy loads and traffic come some very stringent tensile and puncture requirements, and here a woven geotextile is often more in demand;
Drainage;
Where a considerable volume of water must flow, and stable filtration is desired, then high-permeability and stable filtration products are required. Project specifications often seem to favour non-woven, needle-punched products;
Installation Environment;
Where exposure to chemicals, sunlight, extreme weather, and other site conditions come into play; and, all of this relates to:
Project Lifespan.