Tunnels take new Scottish water main under major road and river

Tunnels take new Scottish water main under major road and river
Lowering concrete sections into the access shaft for Scottish Water's tunnel under the A77

Scottish Water has tunnelled under a major road west of Glasgow to avoid traffic disruption, and beneath the River Irvine to reduce the impact on the aquatic environment, as part of a £120 million strategic main investment to improve supply and services in Ayrshire and East Renfrewshire.

Tunnels take new Scottish water main under major road and river
Tunnel boring machine

Caledonia Water Alliance (CWA), Scottish Water’s alliance partner, used tunnel boring machines (TBMs) to install a section of the major new water main under the A77 near Kilmarnock and to lay another stretch of the pipe beneath the River Irvine near Hurlford. If the contractors had excavated and installed the pipe using the open cut method, the work would have required at least a lane closure, closures with temporary traffic lights or even a full road closure, causing considerable disruption to traffic.

The tunnelling work, which started in mid-October, took five weeks to complete. A 67 metre-long steel pipe, and a 60 metre-long concrete tunnel (with a 1.2m diameter) to house it, were installed under the road.

Tunnels take new Scottish water main under major road and river
Building the access shaft for tunnel boring under the River Irvine

CWA also installed a 70 metre-long stretch of tunnel, comprising 1.5 metre diameter concrete rings, about four metres below the river bed of the River Irvine west of Hurlford. The TBM excavated about 275 tons of material in the course of the under-river project, with no impact on the river and the aquatic environment. If CWA had excavated a trench to install the pipe this would have required a diversion of the river.

Sean Lavin, Senior Construction Manager, said: “We recognised how busy the A77 is at this location and that is one of the reasons why we opted to construct a tunnel, which doesn’t require any roadworks.

“In addition, although we previously diverted a stretch of the Craufurdland Water further north to install a stretch of the same water main beneath the river bed, we decided to tunnel beneath the River Irvine at Hurlford.

“This was because trenching and diverting the river would have been much more difficult due to the size of the river. At all times during this project, we try to do whatever we can to minimise disruption to road users and the natural environment.”

Strategic main

The overall project involves installing 30 miles of new strategic water main to connect the old Bradan water supply network in Ayrshire with the Greater Glasgow area’s network is expected to be completed in 2020. It will enable Scottish Water to provide over 200,000 customers with greater security of supply and to respond more effectively to operational issues such as burst water mains.

When complete, the investment will enable Scottish Water to transfer water from Glasgow to Ayrshire, and vice-versa if required.

Horizontal drilling

As part of the same project, Scottish Water and CWA installed 3.8 miles of plastic pipe to the Corsehouse Water Treatment Works (WTW) including a stretch under the M77 and A77 using Horizontal Directional Drilling (HDD), a trenchless method of installing underground pipe using a drilling rig on the surface.