Allowable axle load
What is the definition of allowable axle load?
The civil engineering industry is dynamic and vast. Each factor plays an important role. Every aspect is crucial, from understanding soil behaviour to constructing a structure. On-time transportation of construction materials is essential for a smooth construction process. However, efficient transportation requires good transport infrastructure, which includes well-constructed roads. Heavy vehicles have a massive impact on roads. This is where allowable axle load comes into the picture. It plays a crucial role in balancing well-planned transportation and long-lasting infrastructure.
Before understanding allowable axle load, let’s define axle load. Axle load is the amount of weight a single axle can bear. The allowable axle load is a single axle’s weight, defined legally and as per safety measures. Axle loads have a direct impact on the performance of materials like geosynthetics, which is very popular in civil engineering these days.
In ancient times, the need for well-constructed roads was not prevalent. People used horses or bullock carts as transportation, so the roads were also unmetalled. As time advanced and technology kicked in, heavy transportation vehicles were used. With the change in the mode of transportation came the concept of axle load. The idea behind introducing axle load was to prevent the deterioration of road infrastructure.
Axle loads were first introduced in the 1990s by countries that wanted to establish weight restrictions to safeguard the transportation infrastructure. The maximum allowable limit of the axle load is regulated by The World Road Association (PIARC). This international organisation also plays a crucial role in developing and maintaining new guidelines and regulating the allowable axle load limit across nations.
Understanding geosynthetics:
Geosynthetics are made of polymeric or plastic materials. These geosynthetics help engineers solve civil engineering problems. Geosynthetics are of several types, such as:
- Geotextiles are made of plastic fibres. They prevent soil layers from mixing and let water pass through easily. This helps retain soil particles, facilitating a smooth drainage system.
- The primary function of a geogrid is to reinforce the soil foundation. A geogrid is a plastic grid that evenly distributes stress. It helps improve the soil’s weight-bearing capacity and prevents the potential deterioration of the structure at the foundation level.
- Geonets have a similar structure as geogrids. These three-dimensional grids provide proper drainage and reinforcement to the soil.
- Geomembranes are substantial plastic sheets that cover landfills or ponds to prevent leakage.
How do axle loads affect the performance of geosynthetic materials in civil engineering
Axle load has a considerable impact on geosynthetics. If the load is excessive, it can seriously impact their performance.
Below mentioned are ways in which excess axle load impacts geosynthetics:
- Aggravated stress: Excess axle load has an adverse impact on the soil layers. The geosynthetic layer experiences this excess stress. This, in turn, causes displacement, deposition, or even tearing of the geosynthetic.
- Rupture and tearing: If the axle load is excessive on an unpaved road, the heavy vehicle can rupture the geosynthetic product. This can lead to tearing or deposition, leading to loss of efficiency.
- Low drainage efficiency: Excess axle load can increase stress on the geosynthetic material. This can lead to deformation, causing low drainage efficiency and accumulation of water within the soil layers.
How do engineers determine the allowable axle load for geosynthetic materials?
Engineers determine the allowable axle load to avoid excessive stress and failure of geosynthetics. They use a multi-dimensional approach, which is as follows:
- Geotechnical inspection: Engineers conduct a thorough site and geotechnical inspection before concluding the project details. This inspection includes soil testing, understanding soil behaviour, drainage possibilities and acceptance of the settlement.
- Anticipated traffic forecast: The volume and vehicle type are analysed in anticipation. Based on the analysis, the axle load is decided. This also determines the geosynthetic material to be used, which can bear the weight of heavy vehicles without causing any rupture or failure.
- Pavement structure design: Once the initial steps of inspection, traffic forecast, and selection of geosynthetic material are completed, the pavement structure is designed. The design is based on factors like durability and load distribution.
- Safety measures: Safety measures are the backup plan for unforeseen circumstances. In some instances, traffic load or construction errors are not planned. To ensure the smooth functioning of geosynthetic materials, engineers calculate some extra load to avoid any failures.
Allowable axle load plays a significant role in civil engineering. Today, many of the latest software and machines are available to calculate accurate allowable axle load. This discovery has been made to avoid miscalculations and fewer failures.