How geogrids prevent roads from cracking?
A common problem faced by pavement engineers is the development of cracks in highways, roads, and pavements, which may compromise safety in addition to cost implications for maintenance. Geogrids in highways serve one primary function, reinforcement – which provides several key benefits: it improves the structural integrity of subgrade or aggregate layers, reduces stress on other layers, and minimizes strain, thereby delaying the formation of cracks.
Specific geogrids are also used within or below asphalt layers so that reflective cracks can be intercepted and delayed. Geosynthetics have been proven to increase performance and expand the service life of both paved and unpaved road systems.
In this blog, we explain how geogrids achieve these benefits by examining the common causes of road cracking and highlighting innovative solutions.
What are the common road construction challenges?
Cracks, rutting, or potholes compromise the safety of the roads, making it essential to understand their typical causes. Localized depression and settlement are often caused by subgrades that experience water saturation.
- Climate variability: Roads can develop cracks due to variability in climate conditions, especially if the subgrade foundation is not improved during construction. The most typical solution for improving is deeper excavation alongside using aggregate which is expensive. When the climate changes, such as extreme fluctuations in temperature, prolonged exposure to strong sunlight (think of tar melting), or other environmental factors, it can affect the structural integrity of roads. Freeze thaw weathering is a common problem for asphalt paved roads where the temperature shifts are acute. These changes may lead to the development of cracks in the road surface.
- Traffic loads: Typically, when roads are planned, they are designed based on the loads it is expected to carry. For example, the load-bearing capacity of a national highway, state highway and an in-city pavement will vary. Not only the load, but also the volume and frequency of traffic have to be taken into account. The continuous stress from vehicles leads to microscopic damage in the road surface, which, when sustained, causes structural weaknesses that eventually result in visible cracks.
- Inadequate materials: Using poor-quality materials is a major reason roads develop cracks or potholes. Such materials often lack the strength to withstand traffic loads and weather effects. Typically, most roads in India struggle during monsoon due to water saturation and waterlogging in the soil bed. This weakness leads to quicker wear and tear, and vehicular stress exacerbates crack development.
What is the use of geogrids in Indian highways?
Building highway networks that work across all types of soil types, subgrades, elevation, temperatures and rainfall levels requires resilient materials. India witnesses extreme temperatures across the length and breadth of its roadways.
Geogrids are made from durable materials such as polymers, and are designed for this purpose. Geogrids work to improve the performance of subgrade (often quantified as an improved effective CBR) and/or the structural contribution of aggregate base/subbase layers, across a wide range of conditions.
1. Better performance and longer lifespan
Geogrids, used as a reinforcement layer for the subgrade, work specifically on highway or road strength requirements by providing support and reinforcement to the foundation, thus making it more resilient against wear and tear. Whether it is steep slopes, clay soil, aggregate-paved roads, embankments, or bridges, geogrids provide structural reinforcement.
In a high-traffic highway scenario, integrating geogrids as a fortification mechanism within the road structure plays a crucial role in efficiently distributing stress. The high-strength polymers of the geogrid interlock with the surrounding soil and rocks, forming a robust structure that resists deformation under heavy traffic loads. By enhancing soil confinement and reducing lateral movement of aggregate particles, geogrids significantly bolster roads’ load-bearing capacities. By stabilizing the soil mass and aggregate layers, geogrids contribute to maintaining the integrity of the road structure. This prevents the development of cracks and bumps that typically result from prolonged exposure to substantial loads. This is beneficial not only for new installations but also for highway lane repairs and isolated crack repairs.
2. Strengthening roads with geogrids:
Since geogrids are made from polymers, they work across a variety of terrains, allowing for maximum land utilization by improving soil stability and cohesion. A common application is placing them within the layers under the paved road surface to provide reinforcement and distribute loads more effectively. For example, a biaxial geogrid (like SGB) is strategically placed at the base of the aggregate layer. When subjected to vertical traffic loads, the aggregate attempts to move laterally. The geogrid resists this lateral strain through its tensile strength, effectively confining the aggregate. This confinement creates a mechanically stabilized composite layer out of the granular sub-base, which can then distribute loads more effectively over the underlying subgrade. The geogrid serves as a reinforcement mechanism, significantly enhancing the overall load-bearing capacity of the pavement structure.
3. Mitigating asphalt road cracking:
Geogrids serve as a preventive measure against cracking in asphalt roads, especially reducing the reflective cracks caused by propagating cracks from the underlying layers to the surface. They reduce the incidence of cracks, expand road service life, and improve the ability to be loaded.
Consider an asphalt road constructed in an area prone to ground movement, leading to crack development. When special asphalt reinforcement geogrids are integrated within or immediately below asphalt, they act as a tensile reinforcement element to significantly delay the spread of cracks on the surface from the underlying layers. The geogrids used in the base or subbase enhance the overall structural integrity of the road by interlocking with the aggregate/soil, which reduces stress on the asphalt layer, reduces cracking. This preventive measures significantly improve the durability of the road, making it able to withstand heavy loads and ensure a longer lifetime.
4. Sturdy roads on soft ground:
In areas with soft or weak ground, the use of geogrids is helpful in soil stabilization and reinforcement, which is a core function of geogrids. By providing additional support to the road structure, they’re an excellent choice for road-building material to helps keep the terrain stable. This application is especially crucial for the construction of roads for vehicles and rail systems, where the ground conditions may be sub-optimal.
In Andhra Pradesh, India, a container yard faced challenges due to soft ground consisting of marine clay (or marine soil) with a high groundwater table. The subsoil had a lack of sufficient load-bearing capacity for the container stack and to reach the stackers. To deal with this issue, a ground improvement project was started using a geogrid reinforcement system. Visakhapatnam Port Logistics Park Ltd., the client, recognized the necessity for improvement due to the low safe bearing capacity of marine clay, which posed difficulties for construction vehicles. The proposed solution involved incorporating two layers of geogrids within the Wet Mix Macadam (WMM) layer, thereby avoiding expensive and environmentally harmful soil replacement.
In order to create a solid base for later layers, the road construction process started with the preparation and leveling of the existing subgrade. Coarse sand was added for additional reinforcement after a layer of crusher dust was applied to improve subgrade stability. To ensure a solid foundation, moorum filling was added to compact the layers. A geotextile layer functioned as a filter and separator above the Moorum layer, enhancing layer performance and integrity. By offering separation and filtration, the addition of a 285 GSM PP non-woven layer – a geotextile fabric created from bonding together polymer filaments or staple fibers – helped to preserve the integrity of the pavement layers. To improve support and efficiently distribute loads, a granular sub-base was added. Two layers of biaxial geogrid (such as StrataGrid biaxial – SGB) reinforcements were carefully positioned within the Wet Mix Macadam layer to produce a mechanically stabilized layer (MSL) that could support heavy loads. Wet Mix Macadam was used to finish the road structure. After that, a bedding layer of sand was added, and the wearing course was made up of paver blocks. (If Dry Lean Concrete (DLC) were used, it would typically function as a rigid sub-base layer, placed directly on the prepared subgrade and below the Wet Mix Macadam (WMM) or another base course. It would not be placed under a sand bedding layer for pavers.)
5. Cost savings for road maintenance:
The use of geogrids or other intervention materials, such as geocomposites and geocells, allows for site-specific improvements and cost savings.
Strata Geosystems’ technically advanced products in particular, given their custom development for roadways, reduce the need for extensive soil work, prevent cracks, and enhance overall road performance, resulting significantly in cost reduction. This advantage makes geosynthetics an attractive option for sustainable and budget-conscious highway or in-city road construction projects.
With their ongoing innovations, various types of geosynthetics, such as geogrids, geocells, and geocomposites, continue to meet diverse industrial needs. Engineers are urged to choose products that are particularly compatible with project requirements, such as road improvement, landscape stabilization and soil reinforcement. Due to their longevity, strength, and environmental benefits, these materials are an intelligent choice for engineers seeking to build durable and sustainable infrastructure. To learn more about how our geogrid solutions can address some of your most difficult civil engineering problems, contact us now.