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THINK GREEN

MEETING REPORT

Report on Sustainability in geotechnics, the biannual Yorkshire Geotechnical Group seminar held in Wakefield on 21 April 2004, by Jim Martin, Cementation Foundations Skanska.

What does sustainability mean for geotechnics and how can engineers deliver better products and services for people and the planet without compromising the requirement for healthy 'green' profits?

The aim of this seminar, chaired by Quentin Leiper of Carillion, was to outline some answers.

Speakers included university researchers, government bodies, engineering consultants and contractors.

Each showed how sustainability could only be achieved through careful thought and good communication between each of the stakeholders from a project's outset.

David Anderson of Network Rail began by discussing sustainability in a commercial environment. He examined how a business decides to construct and how it views a proposed project in terms of costs (construction, running, maintenance and demolition), environment, sustainable development and life span.

Anderson approached sustainability from the 'top down' and discussed how providing sustainable solutions was an important part of corporate social responsibility.

Helen Restall of the Environment Agency examined a sustainable solution for remedial works at the flood storage area at Branston Island on the River Witham in Lincolnshire.

Work involved raising and reprofiling an embankment. Design had to contend with peat below the embankment, a soke dyke next to it and an 11kV overhead power line running above it.

A standard solution would have involved building a broad-based clay bank to spread the load, which would have meant filling in the soke dyke and digging a new one, causing considerable environmental disruption as well as requiring rerouting of the power line.

An alternative solution, using tyre bales as lightweight infill, was chosen. Each bale contains an average of 100 used tyres compressed into a single 'building block' The bank design meets engineering requirements and retains the dyke, using almost 10,000 tyre bales (1M tyres) - about 10% of the tyres normally sent to landfill each year in the UK.

Michael Brown and Colin Smith of Sheffield University then discussed sustainable urban brownfield regeneration. Brown introduced the research consortium of SUBR: IM (Sustainable Urban Brownfield Regeneration: Integrated Management) which aims to produce integrated and sustainable solutions for brownfield regeneration.

Smith then looked at one particular problem the research group is tackling, restoration of acid tar lagoons. These are the waste residue of petrochemical processes and can cause huge problems for the environment and people living nearby.

The University of Sheffield is researching ways these sites may be remediated or contained.

Research includes dialogue with all of the stakeholders, including local people, in how best to approach the problem of these acid tar lagoons.

Janine Franklin of Arup showed how construction projects benefit from sustainability appraisal.

This measures how a project, scheme, plan or strategy contributes positively and negatively to sustainable development. Its aims to raise awareness, act as a communication tool and lead to continual improvement. Franklin emphasised that sustainability appraisal should be integrated into a project from the start and that it is an iterative process.

The appraisal makes all of the potential issues in a project explicit from the outset and keeps decision-making transparent throughout.

Decisions taken are then more defensible and robust and may often be more sustainable as a result of communication between project stakeholders.

Colin Serridge of Pennine followed with a presentation on the use of reclaimed material rather than primary aggregate in vibro stone columns. The use of these materials reduces demand on natural aggregates, lowers associated environmental disturbance and transport and avoids waste disposal in landfill.

Recycled and secondary aggregates now form 30% of the total used in vibro stone columns. Recycled aggregates include crushed concrete, spent railway ballast or demolition waste while secondary aggregates could include metallurgical slags or waste rock.

Quality control procedures have increased the amount and types of waste material which may be used, increasing their role in the future.

Stephanie Glendinning of NuGround and Newcastle University presented the next session on electro-kinetic dewatering of soils and waste.

Electro-kinetics is a form of electro-osmosis which can be used to increase the flow of liquid through soils by increasing the electro-osmotic permeability - by up to 10 -4 in certain clay materials.

Newcastle University and its subsidiary company NuGround have researched how this dewatering process may be used in engineering applications.

This has led to the development of a geosynthetic membrane with inbuilt electrodes which can be used as electro-kinetic reinforcement.

There are many potential applications including land reclamation, foundation strengthening, consolidation, reinforced soil, volume control in clay embankments, plus dewatering of sludge lagoons and mine tailings. Some of these processes result in useful construction materials from waste slurries.

Hugo Wood of High Point Rendel and Keith Sleightholme of Skanska (UK Civils) explained how PFA and mine waste was reused on the Selby Bypass. An earthworks deficit along the route meant reuse of waste materials would reduce the amount of primary aggregates used.

This saved money and reduced environmental and social impacts by lowering the number of lorries delivering aggregate.

Finally, Adrian Fox of Atkins showed how the problems of flooded disused underground mines could be dealt with in a sustainable manner.

The objectives for mine water treatment are to reduce the effects of contamination and the preference is for passive treatment using reed beds and natural gradients rather than using pumped schemes and/or chemical treatments.

At Den Burn in Fife settlement and aerobic wetlands were used to treat contaminated water. Maintenance will include sludge removal and dewatering once a year and wetland replacement every 15 to 20 years. However, the wetlands were built in cells so they could be replaced in stages.

It is clear from the presentations that there are no hard and fast rules as to how a sustainable solution should be found. It is hoped that exposure to these novel ideas and new technologies may lead to greater consideration of sustainability in design.

lPresentations are available on CD from Jim Martin, email: jim. martin@skanska. co. uk

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