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Contributed by Strata Global
Road connectivity is what has led to the growth of human civilization. While many parts of the world remain unconnected, despite so many decades of progress, roads remain a subject of engineering challenges. 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 – a class of geosynthetics – play a vital role in reducing cracking in new pavements and asphalt, delaying the onset of reflective cracking. They provide a stress relief layer and prevent or delay top down/bottom up cracks into the subbase and/or subgrade.
Geosynthetics have been proven to enhance the performance and extend the service life of both paved and unpaved road systems. In India, geogrids have been used in highways, runways, hydro-projects, or ports for over three decades now. Some examples include:
Airport Runway, Ahmedabad, Gujarat (1988): Geosynthetics, specifically non-woven geotextiles, were used as a pavement overlay to reduce reflective cracking in the runway of this airport. This application demonstrates the use of geosynthetics in improving the quality and durability of the infrastructure of airport runways.
Salal Hydro-electric Project, Jammu and Kashmir, Reinforced Soil Systems (1990): Geosynthetics in this project were used specially for reinforcing soil to enhance the stability and structural integrity of the infrastructure. This application successfully contributed to the overall success and longevity of this project.
In this blog, we explore the various factors contributing to road cracking and innovative solutions paving the way towards crack-free roads. As a starting point, geogrids in highways or roadways serve four main purposes: reinforcement for subgrade, minimizing cracking, load transfer, and stress relief.
What are the common road construction challenges?
Cracks, rutting or potholes compromise the safety of the roads, making it essential to understand the typical causes behind them. Localized depression and settlement are also often caused by subgrades that face water saturation.
Climate variability: Roads can develop cracks due to variability in climate conditions, more so if they are not constructed by improving the subgrade foundation. 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’re 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. It’s not just the load, but the volume and frequency that also 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 inappropriate or low-quality materials when building roads is a big reason they end up with cracks, or potholes. If the materials aren’t strong enough, they can’t handle the weight of traffic and the effects of weather. Typically, most roads in India struggle during monsoon due to the water saturation and logging in the soil bed. This weakness leads to quicker wear and tear, alongside vehicular stress making cracks appear sooner.
What is the use of geogrids in Indian highways?
Road construction comes with a variety of civil engineering challenges for pavement design. 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 effective CBR [California Bearing Ratio] value of subgrade principally, across a wide range of conditions.
Depending on the class of geogrids –uniaxial and biaxial- types, geotextiles, or geocells, different structural weaknesses can be addressed, from site to site. Right from mountains which can be prone to landslides, high traffic national highways to soft soil challenges at different sites –geogrids and geocomposites provide solutions for every single application. Be it asphalt highways, paved, or unpaved roads, longevity is a key consideration.
1. Better performance and longer lifespan
Geogrids – used as a reinforcement layer for subgrade – work specifically on highway or road strength requirements by providing support and reinforcement to the foundation, making it more resilient against wear and tear. Be it steep slopes, clay soil, aggregate paved roads, embankments, or bridges, geogrids allow for 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 rocks, geogrids significantly bolster the road’s load-bearing capacity. Geogrids also protect against soil erosion by locking soil. This prevents the development of cracks and bumps that typically result from prolonged exposure to substantial loads. This is not just limited to new installations, but equally useful to repairs for highway lanes and isolated crack repairs also.
2. Strengthening roads with geogrids:
Since geogrids are made from polymers, they work across a variety of terrains. Thus, allowing for maximum land utilization by improving soil stability and cohesion. A common application is placing it within the layers under the paved road surface to provide reinforcement and distribute loads more effectively. For example, SGB [StrataGrid™ Biaxial], geogrid is strategically placed within the pavement, countering vertical loads from vehicular traffic and generating horizontal forces in the granular layers. Supported by the geogrid, the granular sub-base plays a vital role in distributing loads and providing structural support, while the natural ground forms the base layer. The SGB Geogrid serves as a reinforcement mechanism, significantly enhancing the overall load-bearing capacity of the pavement structure.
3. Ensuring stability on soft soil roads:
Geogrids are particularly useful for roads which have a weak load bearing capacity. By reinforcing the subgrade, geogrids distribute loads evenly. For example, Cock Lane, a vital rural road connecting the villages of Clavering and Starling’s Green, in Essex, in the United Kingdom faced a critical issue due to the erosion of the adjacent River Stort’s bank. The threat of road foundation failure prompted an emergency closure, allowing only pedestrian traffic for approximately 400 metres. StrataGrid™ was used to construct a reinforced soil wall to address the challenges posed by the unstable riverbank.
It’s distinctive features, including a dimensionally stable network of apertures, bidirectional tensile reinforcement capacity, and a UV-stabilized saturation bitumen coating, helped to strengthen the soil along the river bank. The construction process swiftly installed the StrataGrid™ reinforced soil wall along the riverbank, positioned above the existing gabion wall, completing the task in under a week. This expedited response effectively maintained a consistent slope angle of 70 degrees throughout the structure, accommodating a 20 kPa surcharge from traffic loadings on the road, showcasing the geogrid’s efficiency in stabilizing critical infrastructure.
4. Mitigating asphalt road cracking:
Geogrids serve as a preventive measure against cracking in asphalt roads, particularly mitigating reflective cracking caused by propagating cracks from underlying layers to the surface. They reduce crack occurrences, extend road service life, and improve load-carrying capacity. For example, in areas prone to ground movement-induced cracking, integrating geogrids during construction acts as a protective barrier, inhibiting crack propagation.
Consider an asphalt road constructed in an area prone to ground movement, leading to crack development. When geogrids are integrated during construction, they act as a protective barrier against crack propagation. By interlocking with the surrounding soil, as an embedded layer, geogrids enhance the road’s structural integrity, minimizing the spread of cracks from underlying layers to the surface. This preventive measure significantly improves the road’s durability, enabling it to withstand heavier loads and ensuring a longer lifespan.
5. 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 help 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 encountered challenges due to soft ground consisting of marine clay with a high groundwater table. The subsoil lacked sufficient load-bearing capacity for container stacks and reach stackers. To tackle this issue, a ground improvement project was initiated using StrataGrid™ Uniaxial reinforcements. 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 StrataGrid™ Uniaxial reinforcements within the Wet Mix Macadam (WMM) layer, thereby avoiding expensive and environmentally harmful soil replacement.
The road construction process commenced with the preparation and levelling of the existing subgrade, establishing a stable foundation for subsequent layers. A layer of crusher dust was applied to enhance subgrade stability, followed by the addition of coarse sand for further reinforcement. Moorum filling was introduced to compact the layers, ensuring a sturdy foundation. Above the Moorum layer, a geotextile layer acted as a separator, providing additional strength. The incorporation of a 285 GSM PP non-woven layer – a geotextile fabric made from polymeric extrusions – further bolstered the overall structural integrity. A granular sub-base was added to enhance support and distribute loads effectively.
Strategically placed within the Wet Mix Macadam layer, two layers of StrataGrid™ Uniaxial reinforcements created a mechanically stabilized foundation capable of withstanding significant loads. The road structure was then completed with Wet Mix Macadam, a layer of paver blocks serving as the wearing course for a durable and smooth surface, a layer of sand for stability, and a final layer of Dry Lean Concrete, providing a robust and rigid surface suitable for heavy-duty traffic.
6. Cost savings for road maintenance:
The use of geogrids, or other intervention materials such as geocomposites, using a combination of other products like geocells, allow for site-specific improvements and resulting cost savings.
Strata Global’s 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.
Geogrids can be strategically placed within the road layers rather than relying on expensive soil stabilization methods or extensive excavation. As a result of using high-strength polymers, the need for costly soil manipulation measures is minimized, and the risk of settlement issues is reduced.
With their ongoing innovations, various types of geosynthetics such as geogrids, geocells and geocomposites, continue to meet diverse industrial needs. Engineers are encouraged to select products tailored to specific manufacturing requirements, offering soil reinforcement, landscape stabilization, road improvement, etc. Their durability, cost-effectiveness, and environmental advantages make these materials the smart choice in the pursuit of resilient and eco-friendly infrastructure solutions.
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