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Deep basements and tall buildings

In February, 200 delegates gathered at Earls Court Conference Centre in London for GE's Piling and Foundations 2008. Jim Cook, chair of the event and group director at Buro Happold, reports.

The theme for this year's event was 'faster, greener, safer: exploiting technical advances to meet accelerating demand' – and a top notch lineup of experts made presentations, took part in panel discussions and outlined project case studies.

With a series of major infrastructure projects on the ground or in the pipeline in London, including the Olympics and Crossrail, and with overseas markets such as the Middle East enjoying a construction boom, the piling and foundations industry is buoyant.

However, we also face challenges, such as dealing with increasingly challenging ground conditions, the trend for super tall buildings and deep basements as well as the need to design and build sustainably.

Site investigation to piling strategy
This year's conference was kicked off by Soil Mechanics managing director John Grainger and his colleague, principal engineer and technical manager Dick Gosling, who spoke on the translation of site investigation data into piling strategies. Both highlighted the importance of communicating the need for in-depth investigation to clients and the potential consequences of insufficient analysis and quality investigation.

Grainger and Gosling concluded that if clients, specifiers and site investigation contractors work in integrated teams and communicate clearly with each other, costs arising from uncertainties and low confidence on the part of the specifier can be avoided. The session highlighted that while data is often demanded in a format approved by the Association of Geotechnical and Geoenvironmental Specialists (AGS) it is not always provided as such and in any case some contractors are not able to receive or interpret it.

Maximising the benefits of testing
Next up was Keller Ground Engineering chief engineer Derek Egan, who focused on maximising the benefits of pile load testing.

According to Egan, pile testing is proven to deliver cost savings and reduce risks, although it is not a substitute for adequate site investigation. He said that a well planned and executed programme is essential to maximise the benefits of pile testing. But while analysis is important, it should be completed within the framework of experience, to avoid paralysis by analysis.

Egan went on to recommend maintained load tests as the gold standard in pile testing, but acknowledged that dynamic techniques are valuable as part of a planned programme.

Stent Foundations technical development manager Tony Suckling presented the third session on the ICE's redrafted Specification for Piling and Embedded Retaining Walls (SPERW). This was issued last year and has been well received by industry.

Suckling detailed how the new version has been improved, developed and restructured to incorporate the latest thinking on pile testing and construction methods, and enables the specification to be cross referenced with Eurocodes.

Minimising spoil
The development of pile techniques and design to minimise spoil was the theme of a presentation made by Roger Bullivant director John Patch. He said the need to minimise spoil on projects is driven by three factors – cost, environment and safety. Patch advocated the displaced auger piling approach, which, in comparison with other techniques such as continuous flight auger, offers significant cost savings. This is mostly due to the substantial reduction in the volume of spoil requiring transportation and disposal.

Energy piles
New advances in geothermal piling were outlined by Arup Geotechnics director Duncan Nicholson and Skanska geothermal contracts manager Tony Amis. The duo reported that technology, which has been proven in Europe, is increasingly being taken up in the UK on the back of the green agenda.

They commented that recent innovations have reduced the installation costs of "energy piles", which are now cost-effective (in cost per kW) in comparison with other geothermal systems. It was argued that geothermal specialists should be involved with projects at the planning stage, and the speakers described the interface of building mechanical / electrical systems with ground source heat pump systems as vital.
They also mentioned that the Ground Source Heat Pump Association has recently been established in the UK.

Geocentrix managing director Andrew Bond made the final presentation on the first day, focusing on the impact of Eurocodes on pile design and testing. With the UK's national annexure introduced last year, industry is now able to develop designs based on the Eurocodes standard. This allows practitioners to gain experience and build confidence with the new standard ahead of the full introduction of Eurocodes in 2010.

Reusing foundations
Following the day's presentations, a panel discussed the reuse of existing foundations – featuring Building Research Establishment principal geotechnical consultant Tony Butcher, Buro Happold group director Justin Phillips and English Heritage regional archaeological science adviser Jim Williams.

The panel assessed the increasing demand for the reuse of foundations as well as drivers such as the green building agenda, challenges of constructing new foundations in congested sites and the protection of archaeological artefacts. It also looked at challenges faced in reuse including a lack of knowledge about existing building foundations, their ownership and time and expense of testing.

Discussion centred on how such information should be managed for future foundation design, for example, through a central database or storage facility, and also which organisations should be responsible for its maintenance.

Best practice
The day concluded with a series of case studies. Skanska technical director of operations Martin Pedley looked at the piling and foundation challenges associated with high-rise structures. He concluded that innovative design and construction approaches are needed, but that piling methods are not unique to high-rise projects and logistical and geological influences are key factors in foundation choice.

Bachy Solentache chief engineer David Puller and colleague general manager Chris Merridew reported on the East London Line extension. They said the matching of appropriate piling methods with technical expertise adds significant value to major and complex projects. This was realised on the East London Line work thanks to various types of piling testing that highly influenced pile design.

Highways Agency senior geotechnical adviser Alex Kidd and Stent Foundations major projects design manager Mark Pennington looked at piling and stabilisation work to support road widening. They demonstrated that Agency requirements can be met by innovative thinking, but that a single methodology is not the answer for all widening schemes and plant logistics is a key driver.

The day ended with two additional piling cases studies. The first from May Gurney area manager Mike Cowan and colleague contracts manager Neal Willis on Clare College (University of Cambridge). The second by Expanded Piling director Martin Blower focused on the 'Origin' project in Manchester.

Demand for domestic basements
Day two began with a focus on the increasing demand in the UK for domestic basements. Geotechnical Consulting Group director Hugh St John said the trend is driving the adoption of techniques used for work in confined spaces, as well as the development of new and innovative design and construction methods that need to be sensitive to the environment.

The Association of Specialist Underpinning Contractors was quoted as stating that 70% of its work is in the basement and new build market, instead of underpinning. This compares with five years ago, when 80% was subsidence work.

Middle East
Arup director Asim Gaba then analysed the construction boom in the Middle East, reporting that considerable opportunities and challenges remain for ground engineers in the region. While there are ample new business opportunities there, Gaba warned delegates to remain vigilant to geotechnical and geochemical issues that exist in the region's ground. He also urged that continuity and communication was essential between data collection, design and construction.

Engineering a safe and stable workforce

Next a panel discussion, focusing on the need to engineer a safe and stable workforce, featured May Gurney director of business improvement – safety health and environment Chris Heath, Abbey Pynford chairman Paul Kiss and Roger Bullivant director John Patch.

The panel discussed a range of issues including safety, training, recruitment, retention and benefits – and even a four-day week. Importance was also placed on the need to raise the profile of the industry, and to forge new and improved links with schools, colleges and universities to secure the engineers of tomorrow.

Emerging designs and techniques
Mott Macdonald geotechnical engineering director Tony O'Brien then presented on the theme: 'Emerging designs, techniques and projected trends – where are we headed?'

O'Brien's technical presentation was backed up by a series of case studies, including one on the Golden Ears Bridge in Canada.

He concluded by identifying several emerging design methods including pile group behaviour, linear elastic models, stiffness parameters and the key issues of ductability and redundancy.

World's tallest structure
The final session of the conference was a case study focusing on the foundation design and construction for the Burj Dubai building, which became the world's tallest structure in 2007 and is still growing.

Hyder Consulting regional geotechnical director Kamiran Ibrahim, and colleague principal geotechnical engineer Catherine Murrells demonstrated that specialist site investigation techniques (preliminary pile testing, sophisticated laboratory testing and design methods) led to a cost-effective design. Also, high levels of supervision on site resulted in good quality investigation results and a foundation that is acting in accordance with design predictions.

Technology is key to meeting demand
The conference certainly covered a lot of ground, from site investigation and geothermal foundation and pile design, to overseas markets and issues such as recruitment and health and safety, as well as trends for deep basements in London and super tall buildings in the Middle East.

We demonstrated that technology is playing a vital role in helping industry meet accelerated demand for innovative piling and foundation design, and highlighted a series of critical themes, including communication, continuity, data collection and site supervision.
Feedback from delegates immediately after the event was overwhelmingly positive and suggests that delegates found the presentations, panel discussions and case studies thought-provoking and informative.

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