In an Australian first, UEA recently completed the installation of 1200mm SDR11 PN16 HDPE water main via Horizontal Directional Drilling. This bore was under the Wyong creek crossing that formed part of the Mardi to Mangrove Link Project undertaken by John Holland for the Gosford City Council and Wyong Shire Council.
The project called for a 2.1km buried water pipeline from the Wyong River to Mardi Dam, a 19km buried pipeline through the Yarramalong Valley from Mardi Dam to the existing Bunning Creek Tunnel , 2 new pumping stations and associated works. UEA subcontracted to John Holland for the directional drilling works.
The creek crossing was originally planned as a micro-tunnelling project but ground conditions and the depth of the required shafts (10m +) led John Holland to look for alternatives. Because 1200mm, SDR 11 PE water main was not available in Australia and had not previously been installed by Horizontal Directional Drilling, it was not originally considered. However, UEA found a pipe source in Austria and calculated that its Vermeer D300x500 directional drilling rig was capable of installing this pipe in the prevailing ground conditions. A 60” (1524mm) diameter hole was required for installing the pipe, which was at the limits of the Vermeer.
Apart from the difficult ground conditions (alluvial clay, sand, gravel and sandstone), difficult access was a further challenge, with a narrow 10m wide construction corridor over 1.2km providing access to the exit point. A pair of 180mm pipelines was used to return drill fluid from the exit to the entry site. A Morooka tracked transporter, 4×4 Barford site dumpers and 6×6 Moxy dumpers were used for accessing the site, as well as excavators in the 20-40t operating weight class due to poor access and site restrictions.
The pipe had to be sourced from Austria, as this size pipe was not available from local manufacturers. The pipe was shipped to Australia in 11.8m lengths, packed in 8 x 40ft containers. The containers were decanted in Sydney, transported to site by semi trailer and stockpiled there for later welding.
The pipe and welding equipment was tracked overland by a 40t excavator due to the poor site access. KenKar Plastics was responsible for the butt fusion welding of the pipe, as well as the supply and fitting of steel test plates (81mm thick) to the end of the pipe string for pre installation hydrostatic pressure testing. Upon completion of the welding the pipe string was pressure tested to 1600kPa to prove the integrity of the welding process. The pipe string was pressure tested again after installation.
Despite the many challenges, UEA completed the directional drilling works successfully in early June 2011. The installation of 1200mm HDPE pipe via Horizontal Directional Drilling being an Australian first has led to enquiries from other water authorities, and is causing a rethink in the industry about what can be achieved with Horizontal Directional Drilling methodology, which provides significant environmental benefits from reduced ground disturbance over traditional open cut methods.