A major milestone has been achieved on the £100 million Shieldhall Tunnel project in Glasgow.

Scottish Water have now reached the halfway point on the scheme, which will see a 3.1 mile-long waste water tunnel built in the south of the city to improve water quality in the River Clyde and to tackle flooding.

The team behind the development, known as the Glasgow Tunnel Partnership, is a commercial joint venture between Costain and VINCI Construction Grands Projets called CVJV.

Engineers are using a 1,000-tonne, 180-metre-long tunnel boring machine (TBM) to build the tunnel and completion is on track for later this year.

Workers have installed a full circle of giant concrete rings that form the tunnel at a point about 10 metres (about 32 feet) under the east of Pollok Park that is 1.55 miles along the route, marking the halfway point of the development.

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Key highlights include;

• More than 1600 concrete rings of the tunnel (which are 1.5m-long) have been completed

• More than 150,000 tonnes of earth, stone, clay and other aggregates have been excavated

• More than 7.5 miles (12 km) of pipes have been installed in the first half of the tunnel to service the TBM with air and water

• Over 90% of excavated material will be recycled.

Further work is progressing at Queens Park, which has seen construction continue on an exit shaft for the TBM. A smaller tunnel from this shaft to another shaft will be used for newly-installed flume to connect the tunnel to the existing network.

Paul Kerr, Scottish Water's capital investment general manager, said: "We are delighted to have reached this milestone half-way stage in the tunnel construction.

"The Shieldhall Tunnel team includes some of the best and most experienced tunnellers in the world and they are making great progress with what is the biggest project of its type Scottish Water has ever undertaken."

The Shieldhall Tunnel forms part of Scottish Water's £250m, five-year programme of work, launched in 2013, to improve river water quality and the natural environment.

Overall, the programme is the biggest investment in the Greater Glasgow area's waste water infrastructure in more than a century.

(LM)