Out with the old, in with the new

Extensive ground investigation, four types of piling and river scour protection have all been used for the new Surtees bridge in north east England.

The huge piles supporting temporary works on the Surtees Bridge between Stockton and Middlesbrough, north east England, would probably do as permanent foundations for many lesser structures. The steel tubes, 1.07m in diameter and 30m deep, shoulder massive steel frame jetties above, one each side of the river.

From these, Dutch firm BAM Equipment has just driven the last of 44 bored steel cased piles 30m down to Bunter Sandstone bedrock. These will provide the foundations for the two long leaf piers of a new bridge over the River Tees, which will replace an existing crossing for the A66 highway.

Site workers are slotting precast pier sections "like hollow canoes", says scheme contractor Edmund Nuttall project manager Graham Rice, over pile tops ready to be filled with concrete to form a pile cap sitting with its base just below the waterline.

The 20 platforms, hefty enough to carry BAM's 133t Hitachi piling rig and medium size cranes, are a central part of Nuttall's method for rebuilding the bridge. They give it the chance to work on replacement foundations and then the superstructure for new piers one third of the way out into the River Tees.

Platforms help cope with difficult ground and an awkward shape to the river channel, as well as avoiding the need for cofferdams and other complex works. "The channel profile is a V shape and the banks drop quite steeply to 8.5m depths," says Nuttall site manager Rob Sanger. He points out the river was almost a creek at this point until the early 1990s, after which a tidal barrier was completed downstream. Nowadays the water level is almost constant, rising perhaps 300mm if there is heavy rain.

Platforms found in relatively soft ground. Most of the geology in the area is glacial with firm boulder clay, but just at the bridge location there appears to have been an old inlet in the river valley. The material filling it is softer, "a fairly complicated mixture of silts, some stiff to fairly liquid", says Sanger. The silt is interspersed with peat and sand layers.

It is this soft ground that contributed to a gradual failing of the old A66 river crossing. The concrete bridge has been ailing for some time. The deck has overrun its distressed bearings by about 100mm caused by movement in an embankment, stress build up in the foundation and rotation of one of the abutments.

"It seems the embankment on one side had squeezed the ground and caused the approach to move towards the river," says Sanger.

On top of that, concrete at the water line is breaking up, probably due to corrosion effects from brackishness (slight amount of salt) in the water.

Even so, until recently the dual two lane link carrying the important Stockton to Middlesbrough A66, vital for daily commuter traffic, HGV goods passage and local interchange - was just about serviceable. Then the new South Stockport Link Road opened, which included a major junction just west of the bridge. It needs feeder traffic lanes on the A66 to function properly that run as far as the bridge.

So the Highways Agency, with some prompting and finance from Stockton on Tees Borough Council, has decided to replace the old structure with a wider modern version. Renovating the old bridge was looked at, but was thought to be technically too demanding.

In addition the change will allow other upgrading work; the bridge design by the Agency's maintaining agent a joint venture between Halcrow and Colas will give the bridge a 40t load capacity in line with modern 40t truck requirements The design will add better ship collision protection for a river that has become permanently navigable since the downstream barrier was built.

Replacing the old five span bridge has needed careful planning to keep traffic running on the road during peak hours. "Mostly we have to maintain two lanes each way with one lane running at midday and some closures at night," says Sanger

The solution has been to do half at a time, cutting out the old bridge and building the new alongside, and then transferring the traffic on to it. Nuttall is making extensive use of a large crane, a 1200t AK680 hired in from Sarens, which lifted out up to 344t large sections of the old structure. The big crane with its giant counterweights serves also to lift in steel deck sections for the new bridge.

With the old deck removed, site workers installed the two work jetties. Subcontractor Aarsleff has driven tubular piles by vibration and hammer down to a 3m layer of dense sand and gravel overlying Bunter Sandstone about 30m down.

The same company had already installed four separate clusters of nine driven H piles 30m deep on each side of the river bank. These give support to big outriggers on the huge crane, which had to lift large loads and swing them over a big radius.

Once the jetty frames were welded, BAM installed permanent piles working with a 133t Hitachi rig with a 47m high mast. Rig operators vibrated permanent steel casings down to rock head before using a mucking out augur to clean the inside and finishing off with a 3m deep socket drilled into the sandstone. Cages and concrete completed the piles that were cut back to 2.5m above the waterline. There are 22 piles for the full length of one pier.

Meanwhile Aarsleff carried out more driven piling with a row of steel H-¬piles, raked back slightly to form the abutment on each side. The firm also installed 130 of its 300mm2 reinforced concrete piles for the embankment on one side of the bridge, a precaution against future settlement.

The bridge has nine parallel steel girders with Omnia planks across as permanent formwork for a concrete deck above. Four girders make up the first phase, arriving as pairs from manufacturer Cleveland Bridge, each beam just over a span length. A connection element is dropped into the centre to complete the full bridge length of 145m.

The £14.4M contract will finish in October.

Article courtesy of European Foundations (Summer 2007)

Further Info

For further information, contact Peter Bishop, Head of Public Relations at:
Edmund Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
E-Mail: peter.bishop@edmund-nuttall.co.uk