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MOVINGTOWARDS SUSTAINABILITY

Report on the BGA meeting. Is geotechnics sustainable- Held at the Institution of Civil Engineers, London, on 10 May 2006, by Ali Macdonald, graduate geotechnical engineer, Arup Geotechnics.

The meeting was introduced by independent consultant Jan Hellings, who reminded the audience of the three key factors related to sustainability: social, economic and environmental.

Hellings introduced some of the indicators of sustainability and other governmental methods for increasing sustainability in construction.

Among these is the government publication Building a Better Quality of Life - a Strategy for More Sustainable Construction (2000), which includes methods such as reuse of existing built assets, design for minimum waste, energy minimisation and preservation of biodiversity.

The UK government Code for Sustainable Homes is also due for publication shortly and is set to become the dominant national standard for sustainable building, said Hellings.

It is clear, he argued, that sustainability in construction had become a key government goal and he asked: 'What can we as geotechnical engineers do about this-'

Four factors Tony Suckling of Stent Foundations outlined his four key ideas on sustainability that could be applied to any industry: to promote innovation; to reduce costs; to conserve natural resources; and to reduce nuisance to communities/environment.

Suckling chose four piling applications he considered the most important.

1. Vibro stone columns These have a low nes content and can have a high content of recycled material (eg track ballast, crushed concrete aggregate, demolition materials and waste steel slag) which make them more sustainable than other options. It is also possible to set up a crusher on site, thereby reducing transport requirements.

2. Soil mixing While this does not yet have an established market in the UK, there is the potential for a wide range of applications. Currently the binder cost makes it uneconomic compared with other ground improvement techniques, but changes in environmental legislation could make soil mixing a more attractive option. Suckling acknowledged that soil mixing produced a non-homogenous solution, but said this could be allowed for in design.

3. Steel piling Steel is a recycled material which, when used in piles and walls, can be reused, making it more sustainable.

Suckling stressed the importance of considering whole life costs for any option chosen.

4. Capless piles There are great health and safety bene ts in not breaking down piles to form pile caps, but instead to provide continuity of piles and columns. This, coupled with quicker construction and less traffic on site, contributes greatly to sustainability.

Suckling concluded with a plea to involve contractors early in the process to encourage sustainability.

Reuse of foundations The second presentation of the evening examined sustainability through the research of the Reuse of Foundations on Urban Sites (RuFUS) project. This topic has implications for new developments on all sites as it considers both the reuse of existing foundations and the importance of future proofing new foundations for later reuse.

Tony Butcher of BRE introduced the topic using a case history where demolition and pile cap removal resulted in offsite lorry movements and landfill, only for the project to re-import broken concrete for a piling mat. These lorry movements, and the piling activities, would have been unnecessary had foundation re-use been adopted. The opportunity for a more sustainable project had been missed.

A second study showed how the original piles showed better strength than when they were built, potentially allowing them to take higher building loads than new piles.

To avoid these problems, reuse of foundations needed to be considered at an early stage in the project, said Butcher. A full desk study was needed to reveal as much information as possible about the existing foundations, including pile location and length.

Futureproofing new foundations was also very important, argued Butcher. Documenting the as-built construction of foundations, groundworks and other temporary works would assist this process, while the use of 'smart' instrumentation in structures to assess the load distribution during the life of the structure would increase the possibility of their reuse.

The reuse of foundations provided an opportunity to prolong the life of existing and new foundations and make them more sustainable, concluded Butcher.

Ground storage of building heat energy Duncan Nicolson of Arup presented the final subject for the evening, the findings of a report on the multidisciplinary research project investigating the use of ground storage of building heat energy in the UK.

The project investigated groundsourced heat pump systems (GSHPs) as a means of heating and cooling buildings. The project team was led by Arup and comprised Cementation Foundations Skanska, the University of Birmingham, the University of Newcastle and the Environment Agency.

GSHPs (closed systems) work by using the constant temperature of the ground or groundwater beneath a building (typically 10infinityC to 14infinityC in the UK). Pipe loops are placed in the ground to provide cooling in the summer and provide heating in the winter. GSHP systems typically use a third of the energy consumed by traditional heating and cooling systems.

Open systems operate slightly differently. When a large volume of groundwater is present beneath a site, it can be extracted and used to heat or cool the building and then ejected to a river/dock or sewer.

The closed system pipe loops can be installed in dedicated vertical boreholes, horizontal trenches or as a part of the structural piles of the building (energy piles) or retaining walls (energy walls).

Nicholson concluded that the introduction of GSHP systems for residential buildings and small offi ces was accelerating in the UK.

This was mainly because of increasing energy prices, tighter building regulations and planners seeking reductions in carbon emissions, he said.

Many European countries have introduced design, construction and monitoring standards for GSHP systems. The UK should combine the best of these into a UK national guide to help to improve standards, Nicholson said.

Discussion The discussion was chaired by Hilary Skinner of BRE.

John Findlay of Stent Foundations suggested that one of the most important factors in increasing sustainability was to make better use of integrated project teams, enabling a 'big picture' view of the project.

Steve Corbett of Faber Maunsell reminded the audience that in almost all cases it was the cost which drove the solution and suggested the government should be doing more to take the lead with legislation.

Nicholson asked what the criteria for measuring the sustainability of projects should be, suggesting whole life costs or embodied energy.

Research in this area is being done at Cambridge University by Chris Chau and Kenichi Soga.

Chris Harnan of Ceecom highlighted the current lack of detailed information on carbon emissions by asking whether slag or PFA in piles was the most efficient in terms of carbon emissions. The panel agreed they did not know, but that research should be done to find out.

The impact of the geotechnical engineer and added value As part of the discussion an additional slide was presented by Stephan Jefferis of Environmental Geotechnics.

All geotechnical work has an environmental impact but Jefferis stressed that this should not be considered in isolation. Clift and Wright (2000) showed that if added value (in this instance effectively what is received for doing the work) is plotted against environmental impact the resulting plot was sharply convex. While Clift and Wright's work considered manufactured goods, the same argument could be applied to the construction and use of civil works.

Jefferis' argument was that those higher up the supply chain must recognise that they factor in their environmental impact and be prepared to sacrifi ce some added value to reduce the environmental impact lower down the chain (moving from the top curve to the bottom curve).

For example, paying a little extra to ensure that materials are recycled.

Jefferis said that if the government were to introduce effective targets to minimise environmental impact, geotechnics would become an area of immediate opportunity because of the potential for impact reduction at low cost. However, he stressed that the geotechnical community must act collectively to develop the measures of sustainability by which to measure itself and promote improvement before they are imposed on industry.

Conclusions The panel and audience both agreed that they were not fully aware of what sustainability meant for geotechnics and therefore what improvements could be made towards sustainable practices. The analogy was drawn of attempting to direct someone without a map - it is difficult to drive towards more sustainable practices without knowing what these are.

Those present agreed it was important to investigate this issue further and Skinner concluded by suggesting this as a topic for formal review by the BGA and/or ICE.

l More information on sustainable solutions can be found at:

Steel piles: www. webforum. com/steelpiling group

Reuse of foundations: www. webforum. com/rufus/

Energy piles: www. arup. com/geotechnics/ project. cfm- pageid=6208 References Clift RC and Wright L (2000).

Relationship Between Environmental Impacts and Added Value Along the Supply Chain, Technological Forecasting and Social Change, 65, pp281-295, Elsevier, New York.

Jefferis SA (2005). Geotechnology in Harmony With the Global Environment: Dream or Deliverable- 16th ICSMGE, Osaka.

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