Deep Foundations

Sunstainability and Foundations: A Win-Win Situation

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When the topic of sustainability is raised it is often seen as politicized issue that does not deserve a lot of attention. And some of you may have thought just that when you saw the title of this article. But when you think of this term as it was defined by the Brundtland Commission more than 30 years ago (“development that meets the needs of the present without compromising the ability of future generations to meet their own needs”) sustainability makes perfect sense. The objective is simply to allow future generations to live their lives on this earth.

In order to make that possible references are often made to the analysis results of the so-called Vostok ice core. This almost 2 mile long ice core was drilled in Antartica in 2003 and it allowed researchers to chart the CO2 concentration and the temperature change from the present over a period of 420,000 years (see Fig. 1). From these results two things are very obvious: over that period of 420,000 years the CO2 concentration has varied between approx. 200 and 300 ppm and there is a good correlation between the CO2 concentration and the temperature change from the present. Without going into global warming, probably an even more politicized term than sustainability, it should be of some concern that since 1960 the CO2 concentration has gone up from approx. 300 ppm to 400 ppm, and that earlier this year it was reported that for the first time ever the CO2 concentration exceeded 400 ppm for an entire month. It clearly means that we are in unchartered waters and that this rise could well affect the ability of future generations to live their lives on this earth. For that reason it makes only sense that the total emission of CO2 is considered by this generation.

A few years the European Federation of Foundation Contractors and the Deep Foundation Institute developed a Geotechnical Carbon Calculator, a simple and open, though comprehensive tool to determine the carbon footprint of a deep foundation, i.e. the total amount of greenhouse gases produced directly and indirectly when producing the materials required for that foundation and constructing it (expressed in equivalent tons of CO2). By offering this tool to the industry the idea was that the carbon footprint of different alternatives could be compared and that information could then be incorporated in the decision making process.

But as more and more data became available it became obvious that for most foundation types (other than ground improvements) the overwhelming contribution to the total carbon footprint (80 % or more) comes from the materials required to construct the foundation, i.e. the steel and concrete. So reducing the required quantity of materials reduces the carbon footprint, but it generally also reduces the cost of the foundation. In other words, being sustainable could very well reduce cost and thus improve the profitability.

One example of this approach could be increased testing when designing foundations using the Load and Resistance Factor Design (LRFD) methodology. By performing more testing the design methodology allows for a higher resistance factor, which reduces the overall size of the foundation (either smaller or fewer foundation elements). This smaller foundation obviously has a smaller carbon footprint, but even with the increased testing cost the total cost to design and install the foundation is likely reduced.

Another example is the use of fly ash to replace the cement in concrete. Fly ash is a waste product from coal-fired power plants and therefore the carbon footprint of this material is attributed to the power industry and not to the application that uses that fly ash in concrete. But by replacing 20 % of the cement in a typical mix by fly ash (which has a minimal effect on the concrete properties) the carbon footprint of that concrete is reduced by about 15 %., and since fly ash is cheaper than cement the foundation cost is reduced as well.

These are just two examples of design approaches that reduce both the carbon footprint (and thus provide a more sustainable design) and the cost of the foundation. And hopefully because of these examples sustainability will not so much be viewed as a politicized issue, but a practical issue that makes sense for foundation design.

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