As well as The more famous Shieldhall project in nearby Glasgow where engineers are constructing Scotland’s largest wastewater tunnel, Scottish Water is also investing heavily in the drinking water network in the Ayrshire and East Renfrewshire regions of Scotland. While the East Renfrewshire water main project does not have the impressive dimensions of Shieldhall, which boasts a 4.7m diameter and 5km length, it has its own challenges.

The project is part of a GBP 120M (USD 150M) investment into the network.

The first phase involves the construction of a 21km water main, which was designed and built by the Caledonia Water Alliance, a joint venture of Morrison Utilities and Aecom. The steel pipe was 1,000mm in diameter and supplied by FP McCann.

The choice for steel pipe led to one challenge as the location of the Amlaird Water Treatment Works, combined with the need to gravity feed the facility, means that a 4km section of the pipe needs to travel through a peat bog called Fenwick Moor.

Stewart Davis, Scottish Water’s programme manager, explained: “The geological make- up of the area 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 13m 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 stone quantity varied in accordance with peat depth but estimated to be around 1,000t.

The peat bog has presented the contractors with 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. Peat was replaced after completion.

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.

Sean Lavin, the CWA project manager said: “The floating road was made up of tensar geogrid with a teram membrane attached. The stone was 8”-4” graded, dust free, the timber mats were used where better competent sub structure existed such as clay material, the mats are made of hard wood timber and are 5m-long by 1m-wide and are 100mm-thick. We had no problem getting machinery in to construct it. The road can take up to 40 tonne loads without sinking.”

Rail crossing

An additional challenge was pipe installation under an active railway line. For this section ground investigations were undertaken by ESG and a remote controlled, laser-guided Herrenknecht slurry TBM drove through a mixed face of clay and rock. Settlements were kept beneath 25mm and the line did not need to be closed.

Final thoughts

Lavin concluded: “The entire job has logistical challenges be it ground conditions such as hard rock/height restrictions/weight restrictions/working hour restrictions/Water supply for testing only available at the two extreme ends of the pipeline.”

When asked if there was a previous project this work was based on, Lavin added: “It was the experience of construction team. Key members of the team have decades of welded steel pipeline experience in every type of environment but not previously with Scottish Water.

Scottish Water’s Davis added: “The work on the peatland on Fenwick Moor, and under the railway line have presented us with major engineering challenges but we have met or are meeting those challenges head-on and progressing well with this important first phase of the overall project.”

Construction on the project ran from January to December 2016. Tunnelling began on 4 April and completed on 25 August. The whole project should be complete in March 2017. 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.

All Photos: SNS Photography