By Jonathan Tame, technical officer for the British Association of Landscape Industries, the UK’s largest trade association for landscape contractors, designers and suppliers. He has previously worked across the UK managing a range of landscape and civil engineering projects in both the domestic and commercial sectors
Ground reinforcement is nothing new, for time immemorial humans have been utilising materials so to avoid boggy conditions underfoot or wheel; typically using stone or timber to stabilise soil for roads and flooring. Modern materials now allow us to use sustainable, easy to install products to solve age old problems.
Ground engineering is a specialist subject in its own right, more information on this subject is available from the Institution of Civil Engineers. This article looks relatively at simple ground and embankment reinforcement in the context of what is available for landscape construc- tion projects.
Driveway/parking reinforcement for gravel
Gravel driveways can suffer from wear and tear that can make them unsightly and/or unusable over time. Gravel areas can become rutted and end up with a ‘beach’ effect, where gravel is pushed into ridges resulting in an uneven and unattractive area. Another issue with unstabilised gravel is that it can be difficult to traverse with wheelchairs and baby-buggies. Gravel areas can also see weed growth and soggy spots if a sufficient sub-base or drainage is not installed. Weed growth will result in either laborious hand weeding or the application of herbicide. So installing a reinforcing system on a gravel area can, in the long run, save you time and money.
There are a few methods that can be used to reinforce gravel areas but a common method would be plastic grid/cellular systems; there is an ever increasing amount of these available and they are sold under various trade names. Most products available from reputable suppliers are UV stable, weather and rodent resistant and are often made from recycled materials. One should check that the weight/loading specifications meet the requirements of the site; often the weight loading limits (typically vehicles) will depend on the sub-base the grids are laid on, in general, greater weight limits require a greater depth of sub-base. Each site will be different and factors such as site/local topography and soil type need to be considered. The recommended subbase for a domestic driveway with a cellular reinforcement would be between 150 and 450mm. The sub-base depth would need to be increased for heavier traffic or soils prone to movement.
Another benefit of cellular systems is that they can be easily incorporated into traditional or sustainable urban drainage (SUD) systems; if this is the case then construction methods will need to be adjusted accordingly to incorporate drainage pipes, grills or storage tanks. Many suppliers offer easy to follow installation instructions.
Most cellular reinforcement systems can also be used to create reinforced grass areas. Such systems, if installed correctly, can offer an almost seamless effect to unreinforced grass areas, such as a traditional lawn. Reinforced grass areas could also increase the sustainability value when compared to gravel systems. For grass areas there are also a number of products that can be installed over existing turf and require no excavation; the product can simply be pegged onto existing turf and the grass is allowed to grow through. Such products are often used for overflow car-parks and on golf courses and many have features to increase wheel traction.
Some of the systems used for gravel and grass areas can be used on slopes, but check individual product specification for suitability. For larger areas where cellular systems may not be cost effective, erosion control products could be used, subject to an assessment of the site and its suitability for such products. Erosion control products are generally cheaper to buy and install as they can be installed directly onto a prepared surface, rather than having to excavate and lay a sub-base. They can of course be much cheaper and more aesthetically pleasing than installing retaining walls.
There are a large number of products to choose from, with most sold in rolls that are opened up and pegged to a soil surface. Some contain synthetic materials, others are 100 per cent natural and will biodegrade over time, such as coir or jute based products designed to ease establishment of plant material, like grass or groundcover-herbaceous plants or shrubs: the plants roots then become the slope support.
For larger slopes, stabilisation can also be achieved by using honeycomb type products. One only has to watch Grand Designs or similar TV shows to see that typically commercial products are now being used much more for domestic applications; and there is no reason why these products cannot be used in a domestic setting if the need exists and the site allows. Key reasons for using this type of product would be to reduce erosion, add stability to the slope, to increase the useable area on a site and to better manage rainwater. And for those who think using commercial products is above their level of DIY knowledge, well, the success of these products is due to the ease and rapidity of installation on commercial projects.