The international category in this year's British Construction Industry Awards (BCIA) was swept away by two audacious projects, both exemplifying the innovative use of concrete.
BCIA sets out to recognise not merely good design but quality, best practice and safety of the entire construction process from concept to delivery. But this year the judging panel noted that: 'The overall quality and appearance of many of the projects that emerged either as winners or with high commendations was so high that it might seem that these factors had been overlooked. Not so! Brilliant, practical engineering has been to the fore in all categories.' Six project teams were interviewed for the International Award (NCEI last month), followed by on site inspection in Bangladesh.
International Award Sponsored by PriceWaterhouseCoopers
For projects outside the UK for which either the principal designer or the principal contractor is a UK-based British firm
Winner: Bangladesh-UK Friendship Bridge, Bhairab, Bangladesh
Treacherous ground conditions and swirling currents have historically meant that ferries were the only way across the Meghna River. The decision to build a 1.2km long bridge at Bhairab, 80km north-east of Dhaka, carrying a dual two lane highway was therefore a brave move.
The $100M crossing is a post-tensioned concrete box girder bridge constructed from insitu cast segmental concrete balanced cantilevers. It has seven 110m spans and two 79.5m approach spans. Elastomeric bearings transfer loads through twin walled reinforced concrete piers to pile caps 2.5m deep, which spread load into groups of six 2m diameter piles, some as deep as 80m, founded in underlying silty sands.
Monsoon floods swell the river by 7m to a maximum depth of 34m, while the riverbed is made up of silty sand and alluvial deposits up to 40m deep. Scour is a major problem. Testing designs for the foundations to ensure they would withstand the aggressive environment took 33 months.
Permanent 28mm thick steel casings have been used to protect the bridge's 48 piles, each of which required around 200m3 or C40 concrete.
Pile caps and piers in shallower water were constructed behind temporary sheet piled coffer dams, but in deeper water this was not possible. Here, installation of the pile cap was carried out using an innovative 'jack down' technique: Pile caps weighing 2,500t were cast integrally with the piers at high level above the piles and jacked down to the correct level under water. Casting and jacking were carried out using platforms supported from temporary extensions to the permanent steel pile casings.
The sleek sculpted lines of the bridge deck were formed in 4.5m insitu segments using an adjustable travelling shuttering system. These were cast using C50 concrete in four day cycles, with each segment stressed once a concrete strength of 27.5N/mm2 was reached, usually after 14 hours.
Temperatures and humidity in Bangladesh are high, and controlling the heat of hydration was crucial. Ice and chilled mixing water were used, and all aggregates were kept in specially built shaded bays and sprayed with chilled water.
Mixer truck drums were wrapped in damp hessian to keep concrete input temperature as low as possible. Modelling concrete strength gain allowed engineers to programme the period of maximum heat of hydration for the coolest part of the day, between 4am and 6am.
What the judges said
A benchmark for what can be achieved 80km from Dhaka
It is an extremely elegant bridge
Quality of work is excellent
The Institution of Engineers of Bangladesh was astounded that British Standards and quality control were used and achieved throughout
River training works were quite exemplary
It was a difficult location and local methods used where appropriate such as earthmoving by headpans carried by hundreds of labourers
Client: Roads & Highways Department, Ministry of Communications, Bangladesh
Contractor: Edmund Nuttall
Lead designer: Jacobs Gibb
Other firms: Benaim (UK), Halcrow Group
High Commendation: CERN Large Hadron Collider Project, Package 1, Switzerland
The Large Hadron Collider involves a very substantial reconstruction to the CERN particle accelerator which is built into a ring shaped tunnel deep beneath the border of France and Switzerland.
A large cavern to house equipment for the new Hadron collider had to be opened up around existing experimental apparatus which had to remain in use for as long as possible. This was achieved by using a pioneering British-designed roof for the cavern in which subterranean cable stays anchored all support loads high up and remote from the sensitive equipment near to which rock excavation was taking place. The tunnelled cable stay array is a development of a concept first used on the Pergau hydroelectric project in Malaysia.
What the judges said
Engineering innovation driven by the need to keep the existing CERN research project in operation for an extra year
Involves an extraordinary array of subterranean cable stays tying back a vast reinforced concrete cavern roof. It is a large scale development of a technique pioneered on Pergau hydroelectric project in Malaysia and now being applied to Tindaya cavern in Spain
Astounding level of quality and accuracy
A very special project that is a good example of outstanding engineering design.
Client: CE Group of ST Division, CERN Executive
Principal designer: Scott Wilson (Knight PiÚsold project before merger)
Contractor: CCC JV, Joint Venture CERN Civil Contractors
Other firms: EDF, France