Gmac Utilities Ltd prides itself on being able to work in the most difficult and restrictive of conditions, to enable its customers to bring their projects to completion, on time and on budget. Bringing some 30 years of horizontal directional drilling experience, along with now offering many other trenchless and open-cut solutions, from guided auger boring, to timber headings and shaft sinking, Gmac can offer a solution for almost all projects.
Often Gmac is required to work in environmentally sensitive locations and Sites of Special Scientific Interest (SSSIs), from protected rivers to marshes and beaches, with each contract bringing its own list of challenges and often restrictions and constraints. Whatever a project requires, Gmac has the experience and skillset to manage all the environmental risks associated with it, along with the day-to-day risks and challenges that come with any operation.
Recently, Gmac worked on a project in Galashiels, Scotland, on behalf of Caledonian Water Alliance, as part of a project to upgrade a 12 km water main. Working with the main contractor, A.G. Wilson, Gmac used its uprated American Augers DD440T to place two, 420 m shots for 400 mm diameter 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 10 m beneath the bed of the Tweed and through solid Scottish rock, to minimise the risk of drilling fluids contaminating the river.
The bore needed to pass on a curved path below the river so the rig’ start position was placed 100 m from the banks of the river to enable plenty of space to achieve the required depth and compound curve under the river. Gmac’s experienced crew spent a number of weeks on drilling out each 420 m shot at 12 in (300 mm) diameter.
Navigation of the bores was completed using a high-resolution wireline steering tool from Slimdrill, which is accurate to 2% of the depth below the guidance system wire. A Slimdrill steering engineer was on site throughout the operation.
The 400 mm diameter blue SDR11 PE pipes were fusion welded on site using a McElroy Tracstar 500 Series 3 by an AG Wilson team and pulled into place on rollers ready for the pull-in operations.
Once each pilot shot was completed, reaming and cleaning of the hole was performed. First the holes were enlarged with a 24 in (600 mm) diameter hard rock reamer and then using a 20 in (600 mm) diameter barrel reamer the twenty tonne, PE water pipes were pulled in. With onsite mud recycling facilities, using two recycling units comprising R1000E Sitetec Units each with a 1,000 l/min capacity, Gmac minimised the requirement for fresh water procurement to aid the drilling process by cleaning and reusing the fluids used in the drilling process. The mud pump was a Dupagro P25D High Pressure Pump.
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 make the connecting works to the remainder of the pipeline which was being completed in open-cut.