Enjoying environmental and programme benefits from naturally-derived SuDS liners:
As it becomes more and more important to use sustainable solutions in every element of a construction project, naturally-derived products are making this challenge easier. Improved solutions for sustainable drainage systems (SuDS) mean surface water management is another area to deliver environmental benefits on a project.
SuDS liners are an integral part of any new development, used to form ponds, detention basins and swales as well as to provide ground protection under roads and railways. While there a number of options available on the market to suit all types of developments, site conditions and budgets, the one growing in popularity is a geosynthetic clay liner, the bentonite liner – a naturally-derived solution with intrinsic environmental credentials.
This composite product is manufactured by sandwiching bentonite clay between a woven and non-woven geotextile. Once hydrated and confined with an essential cover layer of soil, its particles expand to create an impermeable layer.
The biggest benefit of the bentonite liner is in how robust it is. Its strength and impermeability reduce the risk of punctures and grant long-term protection against ground water seepage. And in the unlikely event it is torn or ripped by sharp rocks or debris, its natural composition allows it to ‘self-heal’ – its high swelling capacity making it expand around punctures.
This durability is why it is being used in more and more developments, particularly in public sector works where its inherent environmental benefits fit with procurement values. They are now in use under roads and railways to seal the subsoil and protect groundwater, as well as in ponds, detention basins and swales, where a SuDS liner’s impermeability is essential to maintaining effective surface water management.
A bentonite liner’s other major benefit is in its ease of installation – offering both time savings and versatility.
Figure 1 – Bentonite Liner installation
Bentonite liners’ natural composition offers slope stability and even the option to form undulating ground, with its stability ensuring upper layers of subsoil and soil are less prone to move.
Additionally, they are not dependent on good weather or specialist labour for fitting. The material requires no welding, taping or even a power source to aid installation. For developments working to strict schedules or in remote areas, this offers distinct advantages to programme planning, negating the need for good weather and specialist workers on the same day.
By comparison, polymer or rubber liners are difficult, sometimes impossible, to fit during wet or windy weather and need on-site welding for installation or repair, if punctured. Man-made also liners lack the environmental credentials of the natural solution.
The savings this ease of installation offers on time and labour, also reducing the risk of downtime costs, means the higher up-front cost of bentonite liners is evened out to make the overall purchase and installation costs close or equal to standard SuDS liners.
The only criticism levelled at bentonite liners is surrounding their weight – the material is heavy, impacting on delivery methods and meaning installation must be properly planned, often to accommodate the use of heavy machinery for placement. However, given its ability to be installed in all weathers, teams can schedule its fitting to coincide with having plant or machinery on site which can aid installation.
For all the positive reasons outlined, it’s clear why more and more contractors and housebuilders prefer to use bentonite liners to reduce their costs, avoid delays and meet important sustainability aims. Working with trusted partners, they are capitalising on expertise and experience to gain the best solutions for SuDS liners.