How geogrids prevent roads from cracking?
Road connectivity 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. Geogrids provide a stress relief layer, preventing or delaying 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, and ports for over three decades. 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 ensure structural stability of the infrastructure. This application successfully contributed to the overall success and longevity of this project.
In this blog, we explain the various factors contributing to road cracking and innovative solutions paving the way towards crack-free roads. Geogrids in highways and 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 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 causes cracks and potholes in roads, is a major reason they develop 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?
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.
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 rocks, geogrids significantly bolster roads’ load-bearing capacities. 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 is also useful 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. 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 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 is reinforced by the geogrid. It distributes loads effectively and provides structural support. This layer rests on the natural ground forming 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 that 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 meters. StrataGrid was used to construct a reinforced soil wall to address the challenges posed by the unstable riverbank.
Its distinctive features, including a dimensionally stable network of apertures, bidirectional tensile reinforcement capacity, and a UV-stabilized saturation bitumen coating, helped strengthen the soil along the riverbank. 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 loads, demonstrating the geogrid’s efficiency in stabilizing critical infrastructure.
4. Mitigating asphalt road cracking:
Geogrids serves 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, geogrids act as a protective barrier. They inhibit crack propagation during road construction.
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 stabilisation 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 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 (SGU) geogrids 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 (SGU) geogrids 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 (SGU) geogrids reinforcements created a mechanically stabilised 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 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.
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.