When was the last time you thought about the stability of the ground beneath your feet? For most of us, this is the kind of subject that rarely crosses our minds, unless we are involved in building our own home or office site. But in an environment where space for development is becoming increasingly limited, and where we are having to build on sites that might not be ideal for large-scale or heavy constructions or roads, how we stabilize the soil before building commercial architecture is ever more important.
Here we take a look at some of the most innovative new approaches, including more eco-friendly alternatives, using biology as engineering, and how these can complement or replace more traditional options.
Issues with existing options:
The oldest soil binding technique, which is still widely used today, is the addition of cement. Although widely available, cement production is extremely energy intensive, and the application process is complicated. The right amount of clay needs to be available in the soil, or the entire process can be compromised.
Bitumen emulsions are another widely used soil stabilization technique, most notably for road bases, but they are not environmentally friendly and can become brittle when dry.
The addition of chemicals such as lime is also common, usually in the form of calcium hydroxide or dolomite. And while this works well with soils that have high clay content, the process demands a huge input of energy and therefore has a less than desirable carbon footprint. In addition, if the materials are not adequately protected from runoff, they can have a negative effect on the surrounding environment due to their high pH, negatively impacting both plant and animal life.
Fly ash :
Fly ash, which is a byproduct of coal fired electric power generation, is another method commonly used for very coarse soils. Unfortunately, it contains heavy metals and other harmful chemicals which can leach into the surrounding water table and soil.
Renewable and eco-friendly technologies:
So what are the innovators coming up with as greener alternatives to all of the above? Let’s find out!
One of the most promising and inspired new technologies is the use of geocell engineering as a way to stabilize road sites, railway tracks, embankments and for general earth and slope stabilization. A ‘mattress’ is created from a series of cells made from a material known as Neoloy, (or Novel polymeric alloy), which are laid out in a kind of honeycomb formation, which can then be filled in with local materials. It is referred to as a cellular confinement system, which takes advantage of the laws of geometry to create a structure that is both strong and flexible. Any cells which remain at the surface (in the case of retaining walls, for example) can even be used as handy plant containers! The shape of the cells make them extremely good at bearing weight and distributing load, which means they can even be used in high stress scenarios such as busy roads.
Using what’s at hand
One traditional method that still makes a lot of sense is the use of construction waste and sub soils which have been created through the clearing of the site itself. Utilizing these materials which are so near at hand makes both economic and environmental sense, as eliminating the need to truck in other components lowers the carbon footprint of the project.
It may sound a bit like science fiction, but using biological enzymes to stabilize soils shows enormous potential. Enzymes are essentially biological catalysts, and just as they help to speed up chemical reactions within our own bodies, the right enzymes can help to bind soil particles together.
They do this by causing the blanket of water which would usually cling to the outside of a clay particle to be shed. As this happens, the particle loses its charge, becoming neutral. Neutral particles exert less force on each other, meaning that they can move closer together. When a force is applied (such as the weight of a vehicle) this has a compacting and strengthening effect on the soil. Less space between the particles also means that less water is retained, further stabilizing the soil structure as a whole.
Better yet, biological enzymes are organic products, and therefore environmentally friendly and renewable. They show great promise in the stabilization of sites for road construction and roadbeds, airstrips, access roads and the like, and have been tested and approved by several authorities including the US Army Corps of Engineers.
It’s interesting to note that both geocell engineering and the use of enzymes draw from nature as their inspiration – and it certainly looks like this is going to be the way forward for sustainable development.