Perco Engineering Services had an answer for this recently during trenchless work on Southern Water’s Slindon to Hardham bulk water transfer scheme in the UK.
Perco drilled three 450-mm diameter crossings on the 10-km pipeline, which was installed by JT Mackley Construction for main contractor Costain/Black & Veatch Joint Venture. In each case, Perco avoided the disposal of large slurry volumes by mixing and recycling the drilling mud on site, in its own recycling plant, instead of using conventional once-through, premixed mud. Installation project manager, Vic Gretton, explains: “When the Environment Agency stipulates trenchless pipe laying, it solves one ecological problem but creates another, because directional drilling normally produces a lot of water and mud that has to be tankered off site afterwards. We needed a directional drilling company with a professional approach to drilling and the recycling plant was an excellent advantage because there was no excess slurry.”
The longest drill, of 152m, was made underneath a culvert, and a second (50-m) crossing was drilled in very soft ground conditions to install the 450-mm HDPE pipe under a stream. Perco also completed a 100-m road crossing under the A29, all as part of the bulk supply scheme between Portsmouth Water’s Littleheath reservoir and Southern Water’s Hardham works.