TPi March 2014

Challenging construction The logistics of transporting the pipe to site, storing it during construction, constructing the water intake in the river and excavating the trench were all arduous thanks to the terrain and the conditions that lasted well into spring. GPS delivered the pipe in 12m lengths in two separate consignments, and GHJ constructed a secure compound at the bottom of the site where the pipe could be held safely until required. The excavators and butt fusion welding machine were painstakingly transported to the top of the site, with the GHJ team having to take into account the risk of landslips and silt entering the river during that process. It took six weeks to transport the required 13-tonne excavators into position at the top of the site and the exacting process involved breaking a route through rock at the rate of just a metre a day in order to create a temporary road. Construction of the weir, carried out to meet the project’s Environment Agency extraction licence, was designed to leave sufficient water in the river to protect native moss and vegetation and to maintain the dramatic character of a waterfall along the route, which belies the new technology being installed in the mountain. Bags of aggregate were used to create a temporary diversion, providing a dry working area so that the water intake could be constructed at the head of the penstock, and GHJ had to monitor the weather carefully throughout this process to ensure that the risk of flash floods was managed effectively. The open trench for the penstock was excavated before the pipe was transported up the mountain to site, and the demanding landscape once again made this a painstaking process.

Cadair Idris

vertical drops next to the working corridor and only limited passing places. We also had to protect the river, particularly where we were constructing culverts where crossings were required. To do this we used stones to filter the water and straw bales on the downstream side of the culverts to trap any mud and sediment.” Careful management of the river was not only important for environmental reasons but was also necessary to maintain a dry trench while the PE pipe installation took place. GHJ created cut off drains in the sides of the trench at a 90° angle to enable water to exit the trench, so that the pipe could be installed quickly once the complete trench had been excavated and to ensure that there was no damage to the trench from water erosion. Flexible approach The PE pipe was transported to numerous safe drop-off points along the route of the trench using a helicopter and specially

Alan Jones continues, “The working corridor was very narrow with just a foot either side of the trench in some places with

adapted handling equipment to protect the pipe from damage during transit, with wind and down drafts proving a signifi- cant challenge on the exposed site. The pipe was laid out in sections and GHJ then used an innovative method of loading the welding machine and tracking it forward to weld the pipe in the trench in a continuous downhill operation, constructing a custom-made steel-frame structure over the welding equipment to protect the joints from the adverse weather conditions. While the PE100 pipe is flexible, the need to install it in both vertical and horizontal alignment with the trench due to the natural contours of the land and the incline of the mountainside made the installation more complicated.

Cadair Idris

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Tube Products International March 2014

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