A hole lotta love

A hole lotta love

Providing the region with a new road tunnel fit for the 21st Century – and a paragon of safety – is being completed at remarkable pace, writes Brian Nicholls.

Any day now, perhaps even as you read this, drivers in the North East will be enjoying entry for the first time into the brand new half of Britain’s biggest construction and engineering project bar London’s Olympic project. For the Tyne’s second vehicular tunnel between Jarrow and Howdon, remarkably, is opening on time – completed in less than three years by 3,500 widely skilled people.

It took 100,000 to build the Great Pyramid at Giza, and that with forced labour, they say. Here individuals appear at all levels, justifiably, to be experiencing now a sense of self-fulfilment. Certainly three key figures that BQ has interviewed exclusively let enthusiasm break through initial restraint as they talked the project through: Peter Hedley, Tyne Tunnel manager at TT2, Paul Fenwick, project director for Tyne and Wear Integrated Transport Authority, and Daniel Clert, project manager for main contractor Bouygues Travaux Publics. They, with TT2 managing director Trevor Jackson have lived and breathed the tunnel’s construction since the hard graft began in 2008 – site preparation in the February, tunnelling work six months later.

Indeed, some have worked much longer on the project; it has occupied Fenwick for 12 years.

They remind us immediately that completion of this second vehicle tunnel forms only part, albeit the major part, of the job representing a £260m capital investment in the North East’s road infrastructure.

Now the first tunnel, completed in 1967, has to be modernised.

So it will be around December 2011, once that has been done, that the new Tyne Tunnel Crossing will be a fully functioning dual carriageway. Nor will it be a day too soon. The existing tunnel about to be upgraded has a capacity of 24,000 vehicles a day but currently receives 38,000.

Clert has worked on many major civil engineering schemes around the world – Metro projects and roads underground on mainland Europe, and in Australia, Singapore and Hong Kong, as well as the new road tunnel in Dublin. Mostly this work has involved deeper excavations, and some projects were about 50km long.

But he refutes any suggestion that TT2 has been simple by comparison.

“While this one was shorter,” he explains. “It had to be fitted into very limited space. So it required deep excavations, complex dredging, and provision for a number of inconvenient but existing installations. Also the level of safety required is very high. This is one of the safest new tunnels ever made.” The tunnel has been built using immersed tube technology in the river section. Instead of direct tunnelling. A deep trench was dredged in the river bed and huge prefabricated sections of concrete laid in, giving 1.5km out of the total 2.6km length of the new carriageway. This method pleased Peter Hedley, because it sustained jobs at A&P Dry Dock in nearbyWalker. The new tunnel has also come about using a “cut-and-cover” technique.

Diaphragm walls standing parallel were erected below ground to give supported space for excavation to progress. Once the walls were cast, the area between was excavated in phases and temporary struts placed between the walls for support.  The tunnel took shape there and then, using base and roof slabs for lateral support.

It’s said one million tons of rubble came out and half-a-million tons of concrete went in. And waste not, want not – the unwanted rubble wasn’t dumped at sea where it would have infuriated fishermen, but into a disused dry dock at Port of Tyne where it was welcomed to provide development land.

The tunnel passes over the top of the existing vehicle tunnel, with less than three metres in depth separating. Again, care was needed. Associated pressure was applied above the existing tunnel to ensure no damage. A top-down technique was applied with roof slabs constructed first, then excavation beneath the slabs to maintain pressure upon the original tunnel structure.

Constant monitoring of impacts on the existing tunnel throughout showed minimal movement.

Amid all this complicated work there was not one fatal or serious injury, nothing worsethan a twisted ankle apparently.

“We’re very proud of that,” Clert says. So time, not safety, proved the biggest challenge. Clert says: “We had to have activity on every part of the site simultaneously. Building from north to south systematically, or vice versa, would have taken 10 years. We’re talking about three years. Had anything gone wrong, we could easily have lost six months to a year. Fortunately there have been no major hitches.” Paul Fenwick says not only were the variable conditions of the ground challenging, the river itself needed environmental awareness – the Tyne is classed as as the best salmon river in England and Wales.

“The Environment Agency and fisheries bodies were concerned about our intentions,” he says. “We had a lot of dialogue with them both before a public inquiry was held – and even since. The river had to be constantly monitored.

“Also, with the cut-and-cover technique of construction, a community had to be severed. There’s a lot of housing eastwards on the Jarrow side, whereas people’s amenities are on the west side, including two schools beside the site – various businesses, too. All had to be taken into account – not just a matter of getting people across the site.” Motorists and truckers using the crossing regularly have been impressed how routeing and diverting has changed regularly and effectively as work has gone on all around.

That required section managers of the construction firms to meet weekly as a communications group with Hedley’s operation staff, while on another level Fenwick and his team liaised with the local authorities concerned, the two consultations partnering throughout.

Hedley says that while the changes affected communities on both sides of the river, mainly Howdon and Jarrow, more compliments than complaints were received.

“We made a point of talking regularly to the communities and circulating information sheets,” he says.

“Meanwhile all the companies have worked in partnership, pulling in the same direction – quite an achievement, perhaps, with 75 sub-contractors involved.” The local authorities were pleased by the sustained traffic flows throughout. And whilethe tunnel seemed quieter sometimes, prompting some belief that vehicles might be using the bridges upriver in Newcastle, driving the extra miles for fear of being held up, Hedley says no.

“When the global crunch came early on there was a little dip in traffic which may have had something to do with fuel prices. It had nothing to do with the construction. Use of the tunnel hasn’t come down. Despite the construction the traffic flows have been managed and journey times actually improved.” How will they feel on the opening day? Daniel: “Relief”. Peter: “Pride and delight for my customers.” Paul: “I echo that and look forward to where the local communities appreciate the change, the users appreciate the increase in service, and the beneficial impact on the economy.

“Personally I’ll miss it.” ........