HDD beneficial for water and sewer construction: BTB

Water and sewer construction can offer a lot to the more experienced HDD contractors and the potential is there for both the HDD contractor and the end client in saving time, disturbance and costs, writes Ed Tenberge, Managing Director of BTB Australia.

The advantages offered by directional drilling can be just as beneficial for water and sewer construction as they are for communications, electrical power and natural gas projects.

While HDD does, indeed, have much to offer builders of segments of the underground public works infrastructure, demand for drilling services for water and sewer projects has lagged far behind that for the “dry” utilities.

The amount of water pipe installed by HDD increases each year, but even though some directional drilling contractors have been making on-grade installations for several years, the trenchless procedure has not made a major impact in the sanitary sewer market.

There are two primary reasons why:

  * The majority of those who operate and plan the construction of sanitary sewer systems are not aware that HDD is suitable for many of their projects; and
  * Many sewer system professionals who are aware of directional drilling do not believe HDD machines are capable of installing pipe at the critical grades essential for gravity-flow sewer systems; therefore they do not consider HDD a viable option.

Both viewpoints are based on either a lack of understanding or outdated information, as the technology to make on-grade bores is available now.

Directional drilling equipment today is capable of handling pipe in sizes that make up much of our sanitary sewer infrastructure. Similarly, guidance electronics designed to facilitate grade control – when properly used – help drillers achieve consistent results that make HDD on-grade installations cost effective for project owners and profitable for contractors.

These facts remain unknown to public works professionals largely because the HDD industry has not promoted the proven technology directional drilling offers the civil engineers, public works engineers and managers who plan sanitary sewer projects.

On jobs appropriate for HDD, significant savings in restoration costs can be realised.

BTB Australia has recently worked on a number of projects involving sewer installations, including pressure sewer installations, gravity sewers and sewer to grade.

At Mernda, BTB has installed 180 m of 150 mm sewer pipe on a grade of 1:158 in solid bluestone rock formation, and is continuing with a number of other similar bores on the same project for MFJ Constructions. The installations are generally through existing properties with limited access, and the time and environmental benefits were a determining factor given the rock conditions.

BTB has also completed two large diameter bores on the Mernda project for Tenix and Yarra Valley Water, also in extreme rock conditions. A third bore crossing under the Plenty Gorge and installation of a 400 mm pressure sewer pipeline are almost complete.

BTB is currently completing work in Flinders, installing a complete pressure sewer system as the primary contractor for Utility Services. Over 13 km of pressure pipeline, fittings and valves have been installed.

These pressure sewer systems are becoming more popular with the utility companies and they offer a great deal of cost and environmental savings as compared to traditional open cut sewer constructions.

 

 

Project Background

Project Owner: Yarra Valley Water

Project Name: Mernda Doreen Flow Control Facilities & Associated Works

Location: Plenty River, South Morang

Head Contractor: Tenix Alliance

Sub-Contractor: BTB Australia Pty Ltd

Project Details

The Mernda Doreen area, north of Melbourne, is undergoing extensive development. It is expected that approximately 20,000 lots will be developed over the next 15 years. Yarra Valley Water is providing both water and sewerage services to the region. Approximately $60million of sewerage infrastructure is being installed.

The Site

Tenix Alliance was engaged by Yarra Valley Water to construct two sewage pressure mains across the Plenty River as part of a larger construction project. The first was a 0.7 km 250 DN PE pipeline at Mernda which was successfully completed in January 2007. The second (featured here) is a 1.5 km 400 DN PE sewage pressure main from Hawkstowe to Vantage Point on the east side of the Plenty River. Approximately 250 m of pressure main under the Plenty River was required to be constructed by Trenchless Technology to protect the environmental and archaeological values of the river and the river bank area. The pipeline passes through land owned by Parks Victoria which is part of the proposed Plenty Gorge Parklands. Geotechnical investigations of the river crossing revealed that rock in excess of 200MPa could be encountered by the contractor.

Technology

Horizontal Directional Drilling or HDD was chosen as the preferred Trenchless Technology as it was perceived to have a lower risk of bore failure, its environmental impact was minimal and the OH&S risks associated with the works were reduced. It was critical from Yarra Valley Water’s, Parks Victoria’s and Melbourne Water’s perspective that the borehead did not become lodged under the environmentally sensitive Plenty River – an open cut excavation borehead rescue operation would never be feasible. Tenix Alliance engaged BTB Australia as its HDD contractor. BTB Australia commenced work with a 160 mm pilot borehole before reaming back with a 350 mm, 450 mm and 500 mm rock reamer. The 400 DN PE pipe was pulled through the bore from the east side of the river.

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