Scottish Water has been overcoming significant engineering challenges on two key stages of construction on a £120m investment in the drinking water network serving customers in Ayrshire and East Renfrewshire.

Work is progressing on the project to install a strategic water main which will benefit more than 200,000 people in much of Ayrshire and parts of East Renfrewshire.

The first phase of the project is the installation of a 13 mile-long section of water main from near Newton Mearns to the Fenwick/Waterside area.

The route of this section of main, which goes over mainly farmland and open moorland, starts at Waulkmill Glen reservoir near Newton Mearns in the north and goes south via Drumboy Hill, close to the M77 and A77 to Amlaird Water Treatment Works near Fenwick, with branches to the South Moorhouse and Corsehouse water treatment works.

No alternative crossing available to tunnelling under railway line 

In one of the key stages of the installation of the 13 mile-long section of water main, Caledonia Water Alliance (CWA), Scottish Water’s alliance partners, have been tunnelling under a railway line near Barrhead, East Renfrewshire to enable us to install a stretch of the pipe.

It was necessary to go under the Neilston railway line at Barrhead, near Balgraystone Road and Balgray Reservoir, because no other alternative crossing method was available. There were, for example, no local roads with sufficient access, width or height that would enable normal open excavation methods to be used.

After carrying out site investigation work, and liaising with Network Rail, Scottish Water started work under the railway in late July/early August.

Using a state-of-the-art Tunnel Boring Machine (TBM), the water company is installing two parallel sections of concrete water main over a distance of about 85 metres each beneath the railway line to the south of Barrhead.

The TBM is about five metres long and is remotely operated by a team at ground level.

Geological engineering techniques used to cross peat bogland

In another major engineering challenge on the same phase of the project, special geological engineering techniques are being used to enable the installation of a 2.5 mile long stretch of the water main where its route goes across peat bogland on Fenwick Moor to the south.

This route across the peat bog was also unavoidable due to the location of the Amlaird Water Treatment Works and the need to gravity feed water to the facility.

Stewart Davis, Scottish Water’s programme manager, said:

“The geological make- up of the area between Amlaird WTW and a tank at Drumboy is predominantly peat bog, which is between 500mm and six metres deep.”

“The peat, by its nature, is a soft and wet material which does not have the competent geological structure to support a steel pipe which weighs four tonnes per 13 metre length when full of water.”

“So our engineering solution was to excavate to competent clay type soil and then fill the ground back up again with imported stone to provide a competent structure to lay the pipe on.”

The reason the utility is not simply laying the pipe on to the clay-type soil is because the pipeline is gravity fed from Drumboy tank and therefore must follow a constant profile that allows the water to flow naturally towards the Amlaird WTW.

The peat bog has also presented the contractors with huge logistical issues in terms of access across this area coupled with the selection and availability of specialist plant such as wide tracked low ground pressure excavators and long reach excavators.

All equipment and materials required to construct the pipeline across this peat bog has had to be transported there via a purpose-built floating stone and timber mat road, which CWA constructed over the first few months of the project.

The road has enabled the transport of more than three miles of 1000mm diameter steel pipe, welding rigs, welfare facilities, trench shoring equipment, pipe bedding stone and general day-to-day construction traffic.

Scottish Water announced in December 2015 that it would improve the water supply network by installing more than 30 miles of new water mains to connect the system in Ayrshire with the Greater Glasgow area’s network.

 The new and expanded network will enable Scottish Water to provide customers with greater security of supply and to respond more effectively to operational issues such as burst water mains and minimise disruption to customers.

 The other sections of new mains will be a section of about 13 miles from the Fenwick Waterside area to Dundonald in South Ayrshire and a section of about six miles from the Pollok area to a reservoir storage tank in the south of Glasgow.