North Lismore Plateau Water Main HDD Complete



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Background

North Lismore Plateau (NLP) is a site approximately three kilometres northwest of Lismore’s CBD which has been identified for future growth. The development is expected to yield approximately 2,079 dwellings including commercial and retail properties. UEA’s role was to consolidate the water main requirements for the new development of the NLP, in order to utilise the existing spare capacity within the Tullera Water Reservoir to service up to 300 new residential dwellings within the district.

Project Overview

The project included the installation of 1,589 metres of 225mm and 1,423 metres of 300mm PN16 PVC water main by open trench. UEA proposed an alternate method of installation by utilising horizontal directional drilling (HDD), which council approved. Due to the installation method changing, the product pipe also had to be converted to 280mm (225mm Internal) and 355mm (300mm Internal) PN16 Polyethylene (PE) pipe. Due to the relocation of the main, 430 metres of 125mm sleave with 40mm product pipe road crossings were also drilled in to service the existing houses.

UEA chose to use one of the two Ditchwitch AT3020 currently within the fleet of drill rigs which mobilised to site in February 2016. For all underbores, UEA pilot bored a 133mm diameter and then back reamed to 430mm for the 355mm main and 330mm for the 280mm main. By the start of May all pipe work had been installed. UEA’s civil crew then linked up all the pipe, installed hydrants, air valves and scour pits. Each house was then connected to the existing system. Works also included testing, flushing and commissioning.

Project Challenges

Many difficulties were encountered during the drilling process, some of which included:

  • Large extremely hard floating boulders. These boulders were difficult to drill through, especially when the surrounding ground conditions were soft. Rather than changing drill heads and possibly damaging cutting teeth, UEA decided to dig up each rock and remove them before continuing to drill. Due to the shallow depth of the main, dig ups were not an issue.
  • Reactive and soft ground conditions. At the start of the project, this combination of ground conditions and travelling at shallow depths meant that the surface level humping became an issue that could cause major damage. Utilising knowledge within the company, the methods and tooling were altered and boring longer shots of large diameter was possible without any damage to existing surface levels.
  • UEA opted to use temporary traffic lights for shutting down one lane. Traffic lights were not able to be turned on until 9:00 each morning due to local traffic restrictions, so additional staff were required each morning to operate Stop/Go until the lights were able to be turned on.

Between the knowledge of UEA’s team, and a close working relationship with council, these issues were overcome with no effect to the project for the client.

For more details on this project or UEA’s horizontal directional drilling projects, contact the Trenchless team at trenchless@uea.com.au or call us on 02 9851 3000.