Key factors for geosynthetics in roadway construction
One of the reasons geosynthetics are preferred over traditional materials, which remain in wide use, is their inherent longevity and superior ability to improve project quality and outcomes. Polymer-based materials offer inherent longevity, leading to reduced maintenance cycles and fewer hazards. This blog explains how selecting the right combination of products for pavement engineering involves seven key areas that influence the final project outcome: Structural Design, Materials Science, Traffic and Loading, Drainage and Hydraulics, Environmental Factors, Construction and Maintenance, and Design Standards and Methods defined by AASHTO, ASTM, NHAI, or other governing bodies. Given these influencing factors, determining the optimal design and the materials required to achieve the desired result becomes crucial.
What are the distinctive properties of geosynthetic materials?
Deploying these materials makes paved roads not just physically stronger but it also offers cost upsides. Each of the below uses form key components of transportation infrastructure planning due to its ability to address soil stability, improve pavement performance, and reduce settlement, and improve the overall longevity of the road.
- Flexibility: A major advantage of Strata Geosystems’ geosynthetics is their flexibility, as they come in lightweight, easy-to-handle custom-sized rolls, simplifying movement on the construction site.
- 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 reduces construction time and costs; however, proper installation by trained personnel is crucial to ensure the material performs as designed.
- Lightweight: Geosynthetics are lightweight compared to traditional construction materials. This reduces transportation costs and simplifies on-site handling. The ability to use thinner aggregate layers is a result of the reinforcement function, which improves the structural capacity of the pavement, not a direct result of the material’s low weight.
- Durability: Since they’re made from polymers, their life is considered to be long and designed to resist long-term degradation. Although subgrade reinforcement materials tend to be affected by soil pH, 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. This durability has led to it being a widely accepted and used product category in construction.
- Resource efficiency: In some construction projects, geosynthetic usage saves natural resources. For instance, it allows for reduced excavation and material transportation for large 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 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:
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 driving roadway performance is the stiffness of soil-geosynthetic composite, achieved 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; that in turn improves load-bearing capacity.
- Tensile strength: When embedded in soil, geosynthetics mobilize tensile forces through interlocking and friction, enabling them to provide lateral restraint and distribute horizontal stresses.
- 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: Because the soil-geosynthetic interface has a friction angle, it determines how effectively the two materials interact under shear. A higher friction angle means better interlock, less sliding, and more efficient reinforcement performance.
- Tensioned-membrane effect: In a paved road, this is a secondary reinforcement mechanism that only activates under significant vertical deformation. Referring to the vertical support provided by a geosynthetic layer (usually a geogrid) when it deforms under a load, this effect creating tensile forces that resist further vertical displacement—like a stretched fabric. As such this mechanism is valuable for highways built on soft, weak subgrades by offering pushback.
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:
While geogrids and geotextiles are flexible materials, their addition to the pavement layers affects overall system stiffness by improving load distribution and maintaining layer integrity. This helps reduce deflection and surface fatigue—especially in high-traffic areas, soft subgrades, or when using Full Depth Reclamation (FDR) techniques. In such cases, geogrids specifically contribute to a stiffer, more stable pavement structure through soil-geosynthetic interaction.
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 address thin or weak pavements, or conditions with extreme temperatures.
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, geocomposites allow for planar flow and minimize pore pressure, and thus improving the shear strength of saturated soils. Geocomposites can perform multiple roles simultaneously—reinforcement, separation, and drainage—making them especially valuable in saturated or unstable soil environments 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, their high tensile strength and ability to interlock with aggregate can lead to a reduction in base course thickness without affecting performance; potentially reducing material costs. By using geogrids, we achieve 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
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 less susceptible to performance loss due to moisture levels compared to unreinforced soil, 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: The stronger the grip, i.e. higher friction, the more stable the structure, because a higher angle at interface means improved shear strength.
- 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 pavement layers. The downside of this standard approach is that with changing weather conditions, roads are susceptible to environmental forces such as torrential rain, and deteriorate with 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), separation (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 (mitigates 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 enhanced. 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 as a horizontal membrane to absorb and redistribute 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 relatively reduced labour costs, geosynthetic solutions can reduce overall construction costs, in some cases by as much as 30-35%
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
While the list below is not exhaustive, it also 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 characteristics: Poor subgrade drainage will influence the requirement for drainage geosynthetics. A geosynthetic with good drainage characteristics can help prevent 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 design thicknesses of pavement layers influence the type and strength of geosynthetic required to achieve desired performance, such as preventing settlement or rutting.
- 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 utilized to ensure pavement performance lives are satisfied.
- Environmental conditions: Climate and environmental site conditions, out-of-plane stresses 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.