By Russell Jones and Neil Dixon
This paper was originally presented at GRI-24, March 16, 2011, in Dallas, Texas, USA. It has been edited for Geosynthetics magazine style and format.
The articles in this series encompass all types of geosynthetics and their applications viewed from the context of sustainability. Traditional solutions are compared with geosynthetic solutions from both cost and carbon footprint perspectives. (from the Geosynthetic Research Institute’s 24th conference, 2011)
The use of geosynthetics in civil engineering applications is often found to provide financial benefits through the reduced cost of imported materials, reduced cost of wastage, and generally more efficient use of resources compared with traditional solutions using soil, concrete, or steel.
In addition, environmental benefits are also often found where, for example, the use of geosynthetic barriers can significantly improve the performance of natural materials as barrier layers. However, other environmental benefits can be obtained by the use of geosynthetic materials when the whole life cycle of the civil engineering project is considered.
This article presents an overview of the impact of geosynthetics on sustainable development and focuses on the view from the U.K. and the rest of Europe.
The past 20 years have seen a growing realization that the current model of development is unsustainable. In other words, we are living beyond our means.
The goal of sustainable development is to enable all people throughout the world to satisfy their basic needs and enjoy a better quality of life, without compromising the quality of life of future generations. The U.K. government is focusing its efforts on four areas:
- climate change and energy.
- natural resource protection and environmental enhancement.
- sustainable consumption and production.
- sustainable communities.
The ability to develop more sustainably will determine the speed and degree of climate change experienced. While some climate change is inevitable due to past greenhouse gas (GHG) emissions, we need to reduce our future GHG emissions to better manage the future impacts of climate change on the environment, economy, and society.
Greenhouse gas control policies in the European Union
In November 2009, the European Commission projected that it will surpass that obligation to reduce GHG emissions as the 15 member states will reduce their domestic GHG emissions to about 7% below 1990 levels during 2008–2012 (Reference 1). Plans by the EU states to acquire international credits through the Kyoto Protocol’s three market-based mechanisms would provide another 2.2% GHG reduction, while acquisitions by operators in the EU Emission Trading Systems may provide an additional 1.4% GHG reduction, and enhancement of carbon removals by sinks may offer another 1.0%.
With additional policies and measures, the Commission projects that the GHG emissions may be around 13% below 1990 levels 2008–2015.
For the post-Kyoto period (beyond 2012), the European Council in April 2009 adopted on the “20-20-20 Policy”—a climate and energy package that requires by 2020:
- a 20% reduction in GHG emissions from 1990 levels.
- a 20% share of renewable energy in the European Union’s final consumption figures.
- a 20% reduction in energy consumption.
A further commitment was made to scale up the GHG emission reduction target to 30% if other developed countries make comparable efforts under a new international agreement.
A carbon footprint is defined by the U.K. Carbon Trust as a measurement of the total GHG emissions caused directly and indirectly by a person, organization, event, or product (Reference 2).
The footprint considers all six of the Kyoto Protocol GHGs: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6).
In the U.K., carbon footprint is measured in tonnes of carbon dioxide equivalent (tCO2e). The carbon dioxide equivalent (CO2e) allows the different greenhouse gases to be compared on a like-for-like basis relative to one unit of CO2. CO2e is calculated by multiplying the emissions of each of the six greenhouse gases by its 100-year global warming potential (GWP).
The U.K. Carbon Trust describes two main types of carbon footprint:
- an organizational carbon footprint covers emissions from all activities across an organization that includes energy use from buildings, industrial processes, and company vehicles.
- a product carbon footprint covers emissions over the entire life of a product or service, from the extraction of raw materials and manufacturing through to its use and final reuse, recycling, or disposal.
However, we can also consider the carbon footprint of a civil engineering structure, and this is how we can compare the sustainable development characteristics of adopting design solutions using geosynthetics with conventional non-geosynthetic solutions. Understanding the potential carbon footprint of alternative design and construction techniques is essential to allow informed selection of the most efficient civil engineering option, and to establish whether the use of geosynthetics will provide advantages over conventional, nongeosynthetic solutions.
This requires a site-by-site approach that considers the nature of the project, the available materials on-site and nearby, supply logistics and site layout. In the U.K., a recent study was commissioned by WRAP (Waste and Resources Action Program) to investigate the benefits of using “geosystems”—i.e., the composite working system in the ground that may, or may not, include a geosynthetic over more traditional construction techniques using concrete and steel.
The aim of the research was to assess whether geosystem-based solutions could be more sustainable than traditional designs as both concrete and steel have high levels of embodied carbon.
The embodied carbon (or carbon dioxide) is a measure of the cumulative energy and, hence, carbon emissions used in the manufacture, delivery, and use of materials in a civil engineering application. The embodied carbon in concrete, for example, comes from the extraction, processing, and transportation of cement and aggregate constituents, together with the production of the concrete and delivery to site.
The WRAP research considered the amount of embodied carbon in several civil engineering projects and compared traditional designs with designs including geosynthetic materials. The results are presented in the WRAP report (Reference 3).
Examples given in the WRAP report are discussed further in Table 1a.
The carbon footprint of products can be calculated using the PAS 2050 methodology (Reference 4) prepared by BSI and co-sponsored by the Carbon Trust and the Department for Environment Food, and Rural Affairs (DEFRA) in the U.K.
PAS 2050 provides a common basis for the comparison and communication of results of carbon footprint calculation. The methodology calculates those emissions released as part of the processes of creating, modifying, transporting, storing, using, providing, recycling, or disposing of goods and services.
The measurements are used to identify key sources of emissions along the supply chain that can, in turn, influence emission reduction initiatives and the development of lower carbon goods. The calculations are also used to compare civil engineering projects with and without the use of geosynthetic materials.
Life cycle assessment
Life Cycle Assessment (LCA) is a tool for measuring the environmental impact of a product during its lifetime.
LCA takes into account a product’s full life cycle—from the extraction of resources, through production, to use, recycling, and the disposal of remaining waste. LCA studies help to avoid resolving one environmental problem while creating others.
This unwanted “shifting of burdens” is where there is reduction of the environmental impacts at one point in the life cycle, only to increase them at another point. The principles and requirements of LCA are given in two ISO standards—ISO 14040:2006 and ISO 14044: 2006 (References 5 and 6).
The European Union recently published a guide for Life Cycle Assessment (Reference 7), which provides technical guidance for detailed LCA studies and provides the technical basis to derive product-specific criteria, guides, and simplified tools. It is based on, and conforms to, the ISO 14040 and 14044 standards.
LCA studies are also used to compare the environmental impact of two competing products or systems used for some purpose. For example, two design solutions for a civil engineering project can be compared and the designer can then select the most appropriate solution based on its environmental credentials.
Examples of carbon footprint reduction using geosynthetics
During the last few years, there has been an increase in the number of published examples that demonstrate the reduced carbon footprint of civil engineering projects when geosynthetics are used.
The WRAP report presents six case histories of the calculation of CO2 saving for civil engineering projects. A summary of the case histories is in Tables 1a and 1b.
Bunds and embankments
In the first WRAP case history (1., Table 1a), a 100% saving in embodied CO2 for waste was achieved. This is typical in cases where the use of geosynthetic materials allows the reuse of poor on-site soils, rather than exporting them off-site, possibly to landfills.
In addition to exporting soils off-site, the original design required the import of virgin aggregate for granular fill. The geosynthetic solution utilized imported lime to modify the on-site fill, so the saving in embodied CO2 is only 67%.
In this case history, the structural component was changed from the original gabion basket to geosynthetic reinforcement and this resulted in an embodied CO2 saving of 96%. The overall saving in embodied CO2 for this example is the highest of all six case histories, at 87%.
The second WRAP case history (2., Table 1a) was a road embankment that required a slope gradient of 1v:2h to limit the structure’s footprint. The original design, therefore, used imported crushed angular stone to form the embankment and disposal off-site of a significant quantity of clay material.
The revised design allowed the use of the on-site clay soils to form the embankment by including geogrid reinforcement. Due to the quantities of excavation on this project, only a 58% reduction in embodied CO2 was achieved for the waste materials.
The introduction of geosynthetic materials into the embankment resulted in an increase in embodied CO2 because no such material was placed in the original embankment design. However, the use of geogrid reinforcement and the reuse of on-site clays led to an overall saving in embodied CO2 of 31%.
The next two WRAP case histories (3. & 4., Table 1b) involve the replacement of reinforced concrete retaining walls with a crib wall and a modular block wall, both reinforced using geosynthetics.
The first of these two case histories (3.) resulted in a 73% reduction in embodied CO2 for both the disposal of waste from the site and the importation of suitable fill material. In addition, a reduction of 70% of the embodied CO2 was achieved by the use of geosynthetic reinforced crib wall, instead of the traditional reinforced concrete retaining wall. The overall reduction in embodied CO2 for this project was 70%.
In the second wall case history (4.), the use of a modular block wall resulted in 100% embodied CO2 saving for both waste and fill because this design did not require any off-site disposal of waste and import of fill material that was required by the original design.
This was because the original fill material was deemed to be unsuitable for use and a higher grade granular fill material was to be imported. The import of geogrid reinforcement and modular block facings instead of the steel reinforcement and concrete, required by the original design, led to a reduction in embodied CO2 of 81%, leading to an overall CO2 saving of 85%.
The fifth case history (5.) comprised the replacement of a sheet pile retaining wall with a steel strip reinforced soil structure with pre-cast concrete panels. In this case history, there was no saving in waste or imported fill material because the same quantities were required regardless of the two design options. However, a saving on embodied CO2 for the structural components of 84% was realized by the use of the revised design.
The final WRAP case history (6.) involved the drainage behind a 4m-high reinforced concrete retaining wall. The original design used hollow concrete blocks as the drainage medium. These were replaced by a drainage geocomposite. Because the geocomposite was thinner than the concrete blocks, an additional quantity of fill was required to make up the difference in thickness and this led to an increase in embodied CO2.
However, a saving of 82% in embodied CO2 was calculated for the replacement of the concrete drainage blocks with the drainage geocomposite which led to an overall saving of 73% of embodied CO2, despite the fact that the drainage geocomposite was delivered to the southeast of England from its manufacturing base in Germany!
A different technique for comparing civil engineering projects using conventional techniques and geosynthetics was used by Heerten (Reference 8). Heerten calculated the cumulated energy demand (CED) and CO2 emissions for both a traditional reinforced concrete retaining wall and a geosynthetic reinforced retaining wall.
Although the geogrid reinforced road embankment construction required approximately 40% more excavated soil, transported and placed as fill compared to the conventional wall, a reduction in CED of approximately 70% and CO2 emissions of approximately 82% was calculated for the geosynthetic solution.
These reductions are in line with the values calculated in the WRAP report and confirm the significant long-term environmental benefits of using geosynthetic materials instead of conventional techniques.
A second example by Heerten considers the design and construction of a road subbase and compares the use of lime stabilization with geogrid reinforcement in the soil.
Because only a relatively small quantity of geogrid was required for stabilization of the subgrade, compared with the significant quantity of imported lime, calculated reductions of CED (81%) and CO2 (96%) were reported. Another demonstration of the significant environmental benefits of using geosynthetic solutions.
The use of geosynthetics can produce real benefits.
Not only are there financial benefits in reduced costs of imported materials and wastage, but there may be short-term environmental and socioeconomic benefits such as reduction in haulage and associated congestion, noise, and air pollution. In addition, long-term environmental benefits can be achieved as LCA can demonstrate significant reduction in embodied CO2 in civil engineering projects that use geosynthetics to optimize the design.
The importance and timeliness of this topic is recognized by the U.K. Chapter of the IGS, which is sponsoring a four-year research project that started in January 2011 at Loughborough University (Leicestershire, U.K.). The project’s aim is to demonstrate the low-carbon credentials of geosynthetic materials in a variety of geoenvironmental and construction-related applications.
The appropriate use of geosynthetic materials can help to achieve the carbon reduction targets set by European governments and other international organizations.
Russell Jones, a principal at Golder Associates (U.K.) Ltd. in Nottingham, U.K., was a member of the Technical Committee for EuroGeo 4 in 2008.
Neil Dixon, Loughborough University (U.K.), was chair of the Technical Committee for EuroGeo 4 held in Edinburgh, Scotland.
1. Europa (2009), Climate change: Progress report shows EU on track to meet or overachieve Kyoto emissions target, Press release IP/09/1703, November 12, 2009.
2. www.carbontrust.co.U.K./cut-carbon-reduce-costs/calculate/carbonfootprinting/pages/carbon-footprinting.aspx, accessed January 16, 2011.
3. WRAP (2009), Sustainable geosystems in civil engineering applications, Project Code MRF116, May 2009.
4. BSI (2008), Specification for the assessment of the life cycle greenhouse gas emissions of goods and services, PAS 2050:2008, ISBN 978 0 580 50978 0.
5. BS EN ISO 14040: 2006, Environmental management—Life cycle assessment—Principles and framework, BSI, London.
6. BS EN ISO 14044: 2006, Environmental management—Life cycle assessment—Requirements and guidance, BSI, London.
7. European Union (2010) ILCD Handbook: General guide for Life Cycle Assessment—Detailed guidance, First Edition, Joint Research Centre, Institute for Environment and Sustainability.
8. Heerten, G. (2009), Reduction of climate-damaging gases in geotechnical engineering by use of geosynthetics, Proc. Int. Symp. on geotechnical engineering, ground improvement and geosynthetics for sustainable mitigation and adaptation to climate change including global warming, Bangkok, Thailand.