Seeking Sustainability: environmentally friendly ground engineering

19 January 2009

Ground improvement specialist, Vibro Projects Limited, a subsidiary of Bachy Soletanche, produced st

Ground improvement specialist, Vibro Projects Limited, a subsidiary of Bachy Soletanche, produced stone columns to an average depth of 4,5 m on the A1 motorway in Dourges, France, for the construction

The concept of sustainable construction is gaining popularity with equipment manufacturers and contractors alike. Becca Wilkins reports on how this ‘greener' approach is being accepted within the specialist ground engineering sector.

Growing concern about the impact construction has on the environment has led the ground engineering sector to consider using more sustainable techniques.

Balfour Beatty Ground Engineering Group (BBGE) has outlined how it is improving its approach to sustainability in the construction of foundations under the mantra of ‘reduce, reuse and recycle'.

Graham Wren, executive director of BBGE told CE all three aspects are important but ‘reduce' is at the root of every sustainable action.

"Reusing and recycling is all about reducing the consumption of natural resources and reducing overall emissions. Figures vary but it is estimated that globally the manufacture of cement accounts for 5% of all man-made CO² emissions. Reducing the amount of cement we use by increasing our use of cement replacements and/or by improving our designs is a high priority."

He added improving the reuse of existing foundations is probably the next most significant area, followed by recycling.

"Most of our products end up buried so the scope for recycling them is limited, but there is scope for increasing the amount of recycled materials we use in our products - such as recycled aggregates and steel."

Sustainable strategy

Viv Troughton, technical director for Stent, (part of BBGE), said carbon content in foundations can be reduced with techniques using materials more efficiently. He added there has been a resurgence in the use of under ream piles and the company has focused on the use of mono piles, which involves building columns off a single pile, "which is a very efficient use of a piling solution."

According to Mr Troughton, carbon content can also be reduced by using ground improvement techniques - using stone columns or other compaction techniques and by using groups of micro piles. In order to help reduce the use of materials the company is also involved in a hollow pile research project.

Chief executive for Keller, Justin Atkinson, said future reuse is a key issue for the sustainability of foundations in urban areas.

"Our vibro stone column systems, being inert and uncemented, can be removed easily and cheaply or reused in any future developments, unlike piling. With very heavy loads, piles may be unavoidable, so we are looking into pile reuse as well."

He added, "When it comes to constructing foundations, our experience is that price and programme time are still by far the biggest considerations, with sustainability featuring a long way down the list of criteria for awarding contracts."

However, he said, environmental credentials are increasingly being included as a qualifier for tender lists and many of the company's ground engineering techniques fulfill customers' needs for cost-effective solutions in addition to having a lower environmental impact than the more traditional foundation techniques with which they compete.

"For example, our stone columns, using only inert stone, are generally considered to be environmentally friendly alternatives to the steel or concrete products for which they are often substitutes. Not only are steel and concrete more expensive, but they also have additional environmental impacts in terms of higher carbon dioxide emissions."

Comparing techniques

In order that customers can compare the cost and carbon content of different piling solutions Stent has developed a ‘Green' SIESTA (Stent Integrated Estimating Application) programme.

Mr Troughton said the company looked at what standards and protocols existed to develop this solution, but there was little clear agreement as to how to proceed.

He added, "Our SIESTA programme has proved very useful for us to be able to compare different solutions both from a cost and carbon point of view. But going forward what's needed for the industry is a protocol so that we can standardise the approach." He added more suppliers should come forward with their carbon figures so that the industry can obtain more accurate results.

According to Mr Atkinson construction markets tend to be "rather conservative" and in some markets, gaining acceptance for alternatives to traditional piling methods can be a slow process.

"We know that, for certain applications and ground conditions, ground improvement strategies using such methods as vibro stone columns or soil mixing can provide equivalent support to concrete piles, while producing less waste and using less or even no cement.

"However, there are still those in the industry who lobby against such techniques, despite their reliability being well proven. We have to continue to educate the industry in our techniques and try to accelerate this process of acceptance," he added.

Mr Atkinson explained the industry should be seeking national and international standards for comparing foundation and geotechnical products and processes to "assist clients and public bodies in specifying and selecting these from an objective position."

Meanwhile, he added Keller offers its customers a choice between traditional foundations and more sustainable alternatives in many parts of Europe.

"We are looking into ways of providing customers with objective data on the relative environmental impacts of alternative techniques, to enable customers to more easily factor this into their purchasing decisions."

Challenge

The ground engineering industry is aware that customers do not want to pay a premium for more environmentally friendly solutions. Therefore, Mr Atkinson said, Keller's challenge is to reduce the environmental impact of its solutions, without increasing (or preferably, while reducing) the cost.

The company is looking into a number of other ways of reducing the amount of carbon content in its foundations, including increasing the proportion of recycled materials used, reducing energy consumption and increasing the use of locally sourced materials.

However, Mr Atkinson said the company has been doing these things for years and therefore, while there is some scope for improvement, it is limited. "However, we continue to focus on these issues," he added.

Apart from its stone columns and soil mixing solutions, Keller uses other displacement systems, such as driven cast-in-situ piling and dynamic compaction, which create no spoil, therefore eliminating the need to transport it to the tip.

Mr Atkinson added, "Indeed, dynamic compaction, like the vibro stone column method, uses no cementitious material at all."

Drilling techniques

It is not only the foundations industry that is beginning to look at more sustainable techniques in ground engineering, the drilling sector too is taking the issue seriously.

Marketing manager for Atlas Copco's rock reinforcement products, Mark Bernthaler, said, "Ground engineering is a growing market for us because contractors see the increasing efficiency of ground engineering applications. There is also more trust and more available references (in relation to performance, previous installations, improved knowledge of corrosion effectiveness and ground condition calculation methods) for them to use this type of technology."

According to Mr Bernthaler, the development over the last year in self-drilling anchors and micro piling has been the introduction of simultaneous drilling and grouting. "This is now a one-cycle operation and therefore increases the productivity significantly," he added.

Sustainable future

According to Mr Atkinson sustainability will become an increasingly important element of purchasing decisions in future because more people within the ground engineering industry are recognising the importance of preserving the earth's resources.

He added, "We expect that, over time, the same focus on sustainable techniques which is now starting to be applied to above-ground construction will increasingly be applied to what is happening below the ground and this is likely to result in a shift towards more sustainable ground engineering techniques."

As European waste regulations start to take effect in the recent EU accession countries, Mr Wren said BBGE envisages a much stronger focus in these countries on site based remediation technologies.

"Another big opportunity lies in the development of sustainable methods for major infrastructure works, because of the large volumes of materials involved and the opportunity to radically rethink the solutions that can be provided."

He added while Green SIESTA on its own won't have a great impact, the company hopes that it can help encourage other companies in the industry to make the same kind of calculations.

"This may speed up the maturation of carbon accounting in construction - which could have a huge impact. You can't improve what you don't control and you can't control what you don't measure - everyone needs to start measuring."

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