Galashiels – Scotland

Winter 2019/20, Gmac worked on a project in Galashiels, Scotland, on behalf of Caledonian Water Alliance, as part of a project to upgrade a 12km water main. Working with the main contractor, A.G. Wilson, Gmac used their uprated American Augers DD440T to place two, 420m shots for 400mm water mains, below the sensitive River Tweed, the busy A70 road and, a high pressure gas main, with no disruption to the local community and no negative environmental impact.

The fourth longest river in Scotland, the River Tweed, is an important SSSI which meant working with a number of ecological constraints to maintain the habitats of otters, salmon and crayfish. To aid in facilitating the protection of the site and its pristine waters, it was vital to drill 10m beneath the bed of the Tweed and through solid Scottish rock, to minimise the risk of drilling fluids contaminating the river. 

The drill needed to pass on a curved path below the river so the rig was placed 100m from the banks of the river to enable plenty of space to achieve the required depth and compound curve.

Gmac’s experienced crew spent a number of weeks on drilling out each 420m shot at 12”, with a Slimdrill steering engineer on site, using a high resolution wireline steering tool which, accurate to 2% of the depth below the wire. 

The 400mm blue SDR11 pipes were fusion welded on site by the Gmac team and pulled into place on rollers ready for the pulls.

Once each shot was through, reaming and cleaning the hole was performed, first with a 24” hard rock reamer and then, a 20” barrel reamer was used to when pulling each of the two, twenty tonne water pipes through. With on site mud recycling facilities, Gmac minimised the requirement for fresh water to aid the drilling process by cleaning and reusing the fluids used in the drilling process.

Often working in challenging winter weather conditions and with long hours on site, both pipes were placed in good time and the site cleared and made good, ready for the main contractor to meet up with the open-cut work.