Key factors for geosynthetics in roadway construction
The applications of geosynthetics in construction of roadways and pavements offer advantages in stability, drainage, and long-life features. Selection, therefore, is a project-dependent task that will require thoughtful consideration of several factors. This blog explains the key considerations when making such decisions. The decision to choose a combination of products for pavement engineering boils down to seven areas that affect the end project itself. These include: Structural Design, Materials Science, Traffic and Loading, Drainage and Hydraulics, Environmental Factors, Construction and Maintenance, and finally, Design Standards and Methods defined by AASHTO, ASTM, NHAI or other governing bodies. With these components affecting the design, and outcomes comes the question of what is the right design to start with and then what materials are needed to achieve the end result.
One of the reasons geosynthetics score over traditional materials, which remain in wide use, are their longevity, and superior ability to improve the quality of the project and outcomes. With polymer based materials comes inherent longevity which means reduced maintenance cycles, and lesser hazards.
What are the distinctive properties of geosynthetic materials?
The use of these materials is because deploying them makes paved roads not just physically stronger, but chemically, functionally and environmentally superior, alongside cost advantages. Each of the below uses form key components of transportation infrastructure planning because of their ability to address soil stability, improve pavement performance, and reduce settlement, and improve the overall longevity of the road.
- Flexibility: The biggest advantage with Strata Geosystems’ geosynthetics –since they arrive in rolls of custom sizes —are that they’re lightweight and easy to handle; hence, the movement on the construction site is easy.
- Rapid installation: With rolls which can simply be rolled out onto the construction site, they can be installed rapidly and efficiently, without any customized machinery. This, again, dramatically reduces the time and cost of construction since you don’t need skilled labor to implement. With Strata Global’s detailed installation guides, we also ensure that the instructions are visual while providing onsite support.
- Lightweight: Geosynthetics weigh much less than conventional construction materials like in-fill materials. This feature lightens the soil compaction process, or the need for high volume of in-fill material, and reduces the load on underlying foundations, especially in regions with weak or unstable subgrades.
- Durability: Since they’re made from polymers, their life is considered to be long and without degradation. This is in stark contrast to typical in-fill or subgrade reinforcement materials that tend to be affected by water, heat, and cold. Since the material doesn’t lose its core properties, they work to prevent pavement failure that might result from erosion, frost heaving, or settlement.
- Environmental safety: Since geosynthetics are made from polymers, they’re also inherently resistant to biodegradation. Such durability has meant the material’s use in construction.
- Resource efficiency: In some construction projects, the utilization of geosynthetics saves natural resources. For instance, it enables minimisation of excavations and material transportation over huge volumes. This is particularly valuable in ecologically sensitive sites where quarrying from distances makes the project expensive, or excavation is not possible.
How do geosynthetics help in road construction?
Geosynthetics are chosen for four broad areas of application in roadway and pavement construction. Geosynthetic products are materials placed in or under pavement structures to improve service performance by reinforcing the soil and improving the soil’s physical characteristics. Their uniqueness makes them valuable, and preferred in modern-day construction. Apart from the structural enhancements that it provides, there are also other considerations that make it a favored choice today.
Roadway stabilization:
This process is of particular value in soft soils conditions, or unstable soils. By using products such as geogrids, or geocells, site engineers can prevent settlement and deformation, enhance load bearing capacity and reduce soil erosion. Each product renders improvements in soil mechanical properties, and while on a case to case basis the specifics will change, we can broadly look at the following reasons to choose geosynthetic materials for roadway stabilization. A core feature is the stiffness of soil-geosynthetic composite in roadway performance through the lateral restraint applied on the confined material.
- Lateral restraint: This is a primary mechanism, especially for base stabilization, where geosynthetics confine aggregate particles and reduce lateral displacement which leads to wider distribution of load-bearing capacity.
- Tensile strength: Through the above mechanism, the soil-interaction with the material leads to improved tensile properties by resisting horizontal stresses and prevents soil settlement.
- Shear strength: Enhances soil stability by transferring shear loads from base layer to tensile loads in geosynthetic layer by creating a mechanically stabilized composite layer.
- Friction angle: Improves soil-geosynthetic interaction, reducing settlement, and alleviates stress concentrations on the subgrade.
- Tensioned-membrane effect – provides vertical support to wheel loads, and controls the subgrade heave between wheel paths.
- Durability: Resists degradation from environmental factors.
Pavement rehabilitation:
Refers to the process of restoring or improving the condition of an existing paved road, which has degraded. This can take on many forms, depending on the technique of rehabilitation, such as Full Depth Reclamation ((FDR), Cold In-Place Recycling (CIR) or Hot In-Place Recycling (HIR). However, this is dependent on the condition of the pavement, and needs to be examined in the context of environmental factors, and an analysis of the type of rehabilitation needed (whether the road needs retexturing, surface treatment, repair etc.) In choosing geosynthetics for this use case, we look at specific improvements that these materials bring.
Flexural rigidity:
Supports pavement layers and reduces deflection. This is typically an issue or challenge that needs resolving in roads where there’s high traffic, areas with soft soils, or if undertaking FDR techniques. Geogrids and geotextiles can often be used in such cases.
Tensile stiffness:
Helps distribute traffic loads and reduces cracking, which is important for Cold In-Place Recycling (CIR) and Hot In-Place Recycling (HIR) techniques. By using a geosynthetic product, in these contexts, we work to improve the load bearing capacity, and minimize reflective cracking. Geogrids, or geocomposites are often used to thin or weak pavements, or conditions with extreme temperatures. Geogrids offer a 100-1000 kN/m tensile stiffness to improve pavement conditions.
Interlayer friction:
Geosynthetics (geotextiles, geogrids, geocomposites) are used to enhance interlayer friction, improving pavement stability and durability. This process enhances bonding between pavement layers without which paved roads undergo delamination, or separation of the layers, leading to unstable roads. Through CIR, HIR or overlay and repair techniques, new interfaces are developed, thus reducing interface shear failure.
Water permeability:
In many geotechnical situations, water permeability within the subgrade, and base grade is an important consideration. Take for example, coastal highways, or roads within ports, mines or abutments under bridges. In such contexts, with heavy moisture saturation, drainage is an important part of the design stage itself. Here, geotextiles which allow for planar flow and minimize pore pressure, and thus minimizing settlement are often chosen for their ability to reinforce, separate and drain –altogether.
Fatigue resistance:
With pavement rehab, the need to improve fatigue resistance of the surface road, becomes a core goal. Roads such as truck routes, industrial parks, inter-state highways, or the kind which sees heavy vehicular traffic or those with high speed requirements are among common sites where fatigue resistance is affected over a period of time. Roads that also have cracking (longitudinal, transverse, or alligator) also become ideal use cases for rehabilitation using geosynthetics as they improve the tensile strength of the structure and a host of other features that make them optimal materials for this purpose.
Base course reinforcement:
Base course reinforcement refers to the technique used in pavement construction to improve the structural integrity and performance of the base layer, which lies directly beneath the surface course of a road or pavement structure. The objective of this reinforcement is to provide improved load bearing capacity, especially in soft soils, reduce rutting and deformation, improve stress distribution and to extend the service life of the pavement itself. When used in conjunction with geosynthetic materials, typically geogrids, the higher tensile strength and other factors mean reduced material costs, resistance to fatigue cracking, and better performance under heavier loads. By using geogrids, we can confer the following advantages through confinement of soil, and tensioned membrane effect.
- High tensile strength: Resists base course deformation and settlement.
- Low creep: Maintains long-term stability under sustained loads.
- High modulus: Provides stiffness, reducing deformation and settlement.
- Frictional properties: Enhances interaction with surrounding soil.
- Drainage characteristics: Prevents water accumulation and erosion which in turn reduces the chances of deformation.
Subgrade reinforcement:
A stable subgrade forms the basis of a strong foundation for a pavement structure (all of the pun intended). Without a stable subgrade, the entire pavement structure can be compromised easily, and there arises a likelihood of localized failures in the pavement. When stabilized well, and correctly, we can even design thinner pavements, and reduce the overall cost of construction. By using geogrids here, there is a lateral confinement of the soil, which allows for load spreading over a wider area. Since it’s also indifferent to moisture levels, it helps manage the effect of moisture on the subgrade performance.
- High tensile strength: Resists soil settlement and deformation over a larger area by distributing the loads efficiently owing to its own junction strength.
- Interlocking mechanism: Prevents lateral movement and thus creates an interlocking mechanism with aggregate particles.
- Friction angle: Improves soil-geosynthetic interaction.
- Tensile modulus: Contributes to the overall stiffness of the reinforced soil layer, reducing deformation under load.
- Creep resistance: Maintains long-term performance under sustained loading conditions
Why are geosynthetics used in road and pavement construction?
For the longest time, road construction has meant using traditional methods of pavement design –which includes excavation of the subgrade, reinforcement through chemical or mechanical means, and applying reinforcement. The downside of this standard approach is that roads are susceptible to environmental forces such as torrential rain, and don’t withstand repetitive loading of traffic –especially under high vehicular traffic conditions.
Layer |
Geosynthetic Type |
Effects on Soil Properties |
|---|---|---|
Subgrade |
Geogrid or Geotextiles |
Lateral Restraint (increases bearing capacity), Tensioned membrane effect (vertical support under deformation), sepration (prevents mixing of layers), Does not significantly alter inherent soil properties |
Base / Subbase |
Usually Geogrids |
Increased stiffness (mechanically stabilized layer), Improved load distribution (reduced stress on subgrade), Enhanced shear strength (due to increased mean stresses) |
Asphalt |
Various (less common) |
Increased tensile strength (migrates reflective cracking), Improved fatigue resistance (extends pavement life) |
Structural enhancements:
The physical improvement to the soil’s mechanical behavior makes geosynthetics valuable in roadway and pavement design applications. Principally, the use of products like geogrids, and geocells means that the soil is confined and its mechanical properties are affected. Their impact varies depending on the layer in which they are used and the specific type of geosynthetic.
- Improved lateral restraint and confinement: when used in the subgrade layer, it prevents lateral spreading of subgrade soil under load, effectively increasing its bearing capacity.
- Tensioned membrane effect: Under significant deformation, geosynthetics provide vertical support to wheel loads acting like a horizontal surface absorbing vertical pressure.
Functional Improvements:
- Separation: Geosynthetics prevent mixing of subgrade and base course materials, maintaining the integrity and thickness of each layer.
- Enhanced drainage: Certain geosynthetic materials facilitate water removal, helping maintain subgrade strength and reduce moisture-related damage.
- Mitigation of reflective cracking: In asphalt overlays, geosynthetics help prevent cracks from propagating upwards, extending pavement life.
- Erosion control: Geosynthetics such as geocells, or geotextiles help prevent soil erosion, particularly important in coastal areas or near waterways. Depending on the application type, each product allows for a wide set of uses.
Mitigation of degradation:
- Durability: Geosynthetics resist degradation from environmental factors, leading to longer-lasting road structures.
- Versatility: Their adaptability allows use in various applications including unpaved roads, highways, landfills, and coastal areas, addressing different degradation concerns.
Cost effectiveness:
Economic efficiency: Geosynthetics are often more economical than traditional methods which rely on thicker pavements or extensive drainage systems. By reducing the need for materials, site logistics, and inexpensive labour costs, Strata Geosystems can impact construction costs by as much as 35%.
Faster construction: Easy installation of geosynthetics reduces construction time and traffic disruptions, leading to cost savings since it arrives in customizable sizes of rolls, for length and width both.
Factors for geosynthetics in roadways
Pavement design is an important aspect of construction –whether it’s national highways, state roads, or for borders. There are conditions to consider –which affect how thick the road should be, temperature profiles, freeze-thaw cycles, and a lot more affect the design itself. While the list below is not exhaustive, it provides an indicative guide into the factors. Other aspects that should influence decision making would include stress analysis, moisture content of the materials, traffic and loading, drainage and hydraulics among a wider list of details.
- Subgrade conditions: The nature of the subgrade, that is, the layer below the pavement, is the first aspect considered in determining the applicability of geosynthetics.
- Soil type: The soil classification, such as clay, sand, or gravel, dictates the class of geosynthetic to be employed and its placement within the pavement structure, among other factors. Soils have a wide range of mechanical properties; some require very specific solutions to work effectively with geosynthetics. For example, clayey soil typically means more cohesion, while sandy soils need more binding and thus need a different quality of reinforcement.
- Subgrade strength: The strength of the subgrade will be used to judge the level of reinforcement required by the geosynthetic. A stronger geosynthetic may be required to prevent settlement and ensure pavement stability where the subgrade is weak.
- Drainage characteristic: Poor subgrade drainage will influence the requirement for drainage geosynthetics. A good drainage characteristic geosynthetic may avoid moisture-related problems if the subgrade has poor drainage.
- Structure of pavement: The pavement structure design will also influence the selection and placement of the geosynthetics.
- Layer thicknesses: The thickness of the respective layers in the pavement structure will determine the amount of reinforcement the geosynthetic applies. Thicker layers may require stronger geosynthetics to prevent settlement.
- Traffic loads: The type of geosynthetic and where the placement will be in the pavement structure is determined by the predicted traffic loads. In areas of high traffic, heavier-duty geosynthetics should be utilised to ensure pavement performance lives are satisfied.
- Environmental conditions: Climate and environmental site conditions, out-of-plane stressors on the geosynthetic, moisture content, and freeze-thaw cycles, among others, are critical since they directly affect the persistence or durability of the geosynthetic. For example, those geosynthetics proposed for cold areas need sufficient resistance to frost.
Any successful application of geosynthetics in roadway and pavement construction must consider the various factors presented. Engineers and contractors need to know the project objective, subgrade conditions, pavement structure, type, properties of geosynthetics, ways of installation, and long-term performance aspects to make proper decisions that enhance the performance and durability of their projects.
The many benefits of geosynthetics include enhanced stability, drainage, erosion control, and reinforcement. These can be attained by selecting appropriate geosynthetics and proper installation techniques.
It cannot be generalized that the application of geosynthetics is single, as one size suits all. Requirements regarding the kind of geosynthetic and its placement are completely dependent on particular projects. All factors considered, engineers and contractors could ensure that geosynthetics are undertaken successfully for each roadway and pavement construction project.