Scottish Water’s Shieldhall Tunnel project, in the south of Glasgow, passed the milestone on 1st May when the tunnel boring machine (TBM) building it reached a point under Pollok Park.
The £100m tunnel will enable Scottish Water to improve water quality in the River Clyde and tackle flooding. At 3.1 miles long, it will be five times longer than the Clyde Tunnel.
Contractor CVJV, a joint venture between Costain and Vinci Construction Grands Projets, began driving the 1000-tonne, 180-metre long TBM in July 2016 and expected to complete tunnelling later this year.
The TBM is tunnelling at a speed of about 120mm per hour, with a rotating cutting wheel with 25 cutters at the front, through challenging ground which includes boulders, clay, hard sandstone, glacial tills and old coal workings. To date, more than 150,000 tonnes of spoil has been excavated and more than 1600 concrete rings of the tunnel (each 1.5-metres long) have been installed, each made up of six curved pre-cast concrete segments weighing 2.5 tonnes. Tunnel diameter is 4.7 metres.
The first half of the tunnel construction has taken it under Bellahouston Park, the Glasgow Paisley Canal railway line and the M77.
Paul Kerr, Scottish Water’s capital investment general manager, said: “We are delighted to have reached this milestone halfway 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.”