Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/721218
SEPTEMBER 2016 WET NEWS 13 ONSITE TRENCHLESS TECHNOLOGY Multi-pulling underground • Not disturbing the ruins of a medieval castle was just one of the challenges faced on a scheme to install a 390m-long pipe beneath the River Corrib. D uring April 2016, Stockton Drilling (SDL) started work on a challenging crossing of the River Corrib in Galway, Ireland. The work was completed on a sub-contract basis for GMC Utilities, the principle contractor for SSE in Ireland. The project involved the installation of a 390m-long HDPE pipe-bundle beneath the River Corrib to facilitate the installation of a 110kV grid connection to the SSE wind park west of Galway city. To complete the work SDL utilised its 250-tonne horizontal directional drilling rig to install a bore of 710mm (28in) diameter into which the HDPE pipe bundle was to be pulled. The HDPE pipe bundle consisted of three 200mm diameter and three 125mm diameter pipes. The installation took place at a site located close to the historic Menlo Castle, a Galway County Heritage site. The drilling work commenced from an entry site on the western bank of the Corrib, with an exit-point set within the National University of Ireland Galway (NUIG) campus. As well as having a width of about 110m, the Corrib flows along a fault line where rock type granite and limestone converge. The area is also a Special Area of Conservation (SAC). Medieval castle These factors, combined with works being required not to interfere with the ongoing activities of the university and not to disturb the ruins of the medieval castle, resulted in the project presenting an array of logistical and technical challenges. In order to overcome these challenges, the HDD profile was designed as a continuous curve from the entry point, entering at 13o to the horizontal and following a vertical radius of not less than 400m. To facilitate the reaming stages of the main bore, two pilot holes were drilled. Both were installed utilising a 170mm (6¾in) diameter down- hole mud-motor, powering a 216mm (8½in) diameter tri- cone drill bit to follow the predetermined profile trajectory to the pre-planned exit point. The first pilot hole had a 125mm HDPE pipeline inserted. This was to be used as a drilling fluid return line during the main bore reaming operations. The second pilot bore was reamed in two stages to the required 710mm (28in) diameter to facilitate the insertion of the HDPE pipeline bundle. In order to install the required pipe bundle effectively, given the pipe sizes involved there was a requirement for a pipe towing head that would pull in five pipes (3x200mm and 2x125mm) at the same time. SDL approached Pipe The drill rig launch site on the Galway project showing the pipe bundle successfully completed pull back Equipment Specialists (PESL), of Stockton-on-Tees, for assistance, given that this is one of the company's specialist areas of operation. PESL offers a variety of pipe pullers for various aspects of the pipeline and trenchless industries. On the first enquiry it was obvious that the PESL Multi Puller would be ideal for the job. The Multi Puller is a Inset: Detail of the final reamer/towing head/pipe bundle assembly The exit side of the bore showing the pipe bundle about to be installed.