Sports surfaces need to be made to the highest possible standard for the elite athletes who utilise them. To guarantee this, there is a delicate balancing act to be found in their creation to ensure the ground itself isn’t damaged by heavy machinery and construction vehicles.
Craig Andrews, Engineering Manager (UK & Ireland) for geogrids-based solutions at Wrekin Products, discusses why it’s crucial contractors bear in mind the load on sport surfaces while they’re being constructed, and how installing a geogrid might be the quick and easy solution they’re searching for.
The geogrid market consists of several innovative products that are still relatively unknown to engineers due to a lack of awareness, meaning many simply don’t know how they can provide an effective fix to the barriers contractors face – particularly when working on more specialist projects, such as sport pitches and Multi-Use Games Areas (MUGA)
Immediate protection for long-term life
Throughout construction, vehicles will be applying stress to the subgrade, which, if not supported, could result in a large level of construction deformation and subgrade strain. To avoid any unwanted long-term issues caused by these, the first step is reinforcement and stabilisation of the aggregate layers.
Without sufficient protection by the founding stone layers, a subgrade that is left to be driven over by machinery is bound to get damaged, which could consequently have a long-term effect on the performance of the surface.
In this scenario, we can refer to the CD 255 document, which sets out the design procedure for pavement foundations in terms of the ability of the foundation to resist loads applied both during construction and the service life of the pavement. While this document focuses on roads, the same principle applies for designing any foundation to support any trafficked surface.
During construction, the stresses in the foundation are relatively high, therefore the stiffness and material thickness of the layer has to be sufficient to withstand the load without damage occurring that might adversely influence the long-term performance. Initially, this requires a geogrid with a reinforcement function, which caters for strength at high strain. Upon completion, the stresses in the foundation will be far lower, which is why it is essential that the foundation is reinforced from the beginning, otherwise deterioration of the upper layers is going to occur more rapidly than anticipated. Subsequently, this requires a geogrid with a stabilisation function, which caters for stiffness at low strain.
This is when a geogrid can really prove its worth, as it provides a layer of reinforcement with stabilisation that’s crucial to preventing the development of early failure to what should be a pristine playing surface.
Consistency is key
The last thing any contractor wants is to cause long-term damage to the subgrade due to stresses caused by vehicles during the construction period. Geogrids act as both reinforcement and stabilisation, offering strength and stiffness when a surface is experiencing high strain or low strain, providing consistent performance, preventing any damage.
Used in composite with the aggregates, they can evenly distribute the applied vehicle loads to the underlying subgrade without causing distress in any of the foundation or overlying layers and ensure the longevity of the surface. This is particularly pertinent when it comes to sports surfaces, as often the ground can be very soft and/or, the surface may be thin, therefore it is at a higher risk of being damaged early on in the construction process.
Given a soft subgrade, by incorporating geogrids along with a value engineered design section, there is also scope for the heavy founding section to be reduced in thickness, sometimes by up to 50%. Net cost savings alone could be up to £20 per square meter, and that’s after the geogrids have been procured. Given the size sports surfaces can be that’s a significant cost saving, even before considering the time saved, overheads, and improved health and safety as well as the environmental benefits.
You might want to ask yourself and your clients – why wouldn’t you want to use geogrids and a value engineered design? No matter what the construction project, there will always be a need for heavy plant, machinery and vehicles, which present a risk to the durability of specialist sports surfaces.
But the benefits of geogrids go beyond simply ensuring the longevity of these surfaces for years following their construction – they also offer a simple and efficient way to save time and money during the construction process itself, allowing contractors additional time and resources to focus on other elements of their project.