A small tunnel for Greater London

4 June 2001 15:44 - BAM Nuttall Ltd

Things have come to an end for project manager John Montgomerie and the Nuttall team. They were based on the south bank of the Thames for ten months with a view of the famous Tower of London and in the shadow of the equally famous Tower Bridge. A spectacular site for the spectacular office of the Greater London Authority [GLA], which can be reached via a Nuttall tunnel.

It's still approximately ten months until the Mayor of London and his 400 civil servants will look out onto the best known 'landmarks' of the British capital from their 'huge headlight'. This eye-catching building was designed by Foster and Partners and is the central element of a development project site along the Thames. There are a further six 'plots' available for building on the site.

Once the site – called More London Bridge – has been completed in 2005, it will be free of cars. 'It will be a pedestrian zone, with hard and soft landscaped areas', explains project manager Montgomerie. 'Our tunnel provides motorists and suppliers with access to the seven buildings.' The tunnel is 300 metres long, 9 metres wide and 9 metres high. Montgomerie: 'The tunnel has two levels. The lower one is to the service tunnel containing the pipes, cables and wiring for the supply of utility services such as water, electricity, gas and telecommunications. The upper one is the road surface at a height of three metres above the service tunnel.'

Nuttall's contract [contract sum is approximately £4.8 million] does not only involve construction of the tunnel, but also construction of an underground equipment room which will house an intermediate station for London Electricity.

Hydraulic struts

The tunnel and the equipment room are built in an open excavation site. 'At several points, the distance between the Thames and the construction site is just five metres. Keeping the excavation dry was a difficult task', says Montgomerie. The sheet piling is sunk deep into the thick London clay, 15 metres below the surface level. At the point where the tunnel widens for the equipment room, Nuttall used hydraulic struts to support the sheet piled walls.' Standard steel props would have been cut to the right length at the construction site itself and would have been extremely difficult to get into position. Together with the subcontractor Groundforce, Nuttall designed a frame that could be positioned much more rapidly and more easily.'