Yanchep Pressure Main, Main Sewer & Collector Sewer

This project involved the construction of a pressure main, main sewer and collector sewer. We were required to utilise a wide variety of construction techniques including both trenchless and traditional methods.

  • Client:

    Water Corporation

  • Location:

    Yanchep, WA

  • Construction Period:

    Nov 13 - Dec 14

  • Key Elements:

    • Microtunneling and auger boring
    • Tunneling through limestone
    • Horizontal Directional Drilling
    • Caisson construction
    • Sewer installation
    • Traffic management
    • Community liaison

Project overview

Water Corporation required an upgrade of the existing Yanchep sewerage infrastructure. This included the decommissioning of an existing wastewater pumping station, construction of a new collector sewer and main sewer. Utilisation of a wide variety of construction techniques including both trenchless and traditional methods was required.

An 8 kilometre DN450 PE pressure main was constructed using several methodologies. A Tesmec TRS 1300 rock saw was used to ensure fast and effective trenching through limestone rock ground conditions. Auger boring machines were employed to undertake four road crossings to ensure minimal disruption to the public. Two sections were installed using horizontal directional drilling (HDD). These included a 630 metre shot through a limestone hill and a 460 metre dual radius shot under existing landscaped park areas.

Construction of the main sewer involved a 140 metre continuous section of DN1200 plastic lined RC pipe beneath a busy roundabout in solid limestone. Accurate results were achieved using a unique combination of slurry microtunneling and auger boring. The collector sewer consisted of 1,500 metres of gravity sewer. Over 900 metres was installed with a Rockman TRW-800 microtunnelling machine in cavernous limestone ground conditions.

The most significant of the microtunneling drill shots was a 160 metre continuous section which was drilled from 12 metre deep RC caissons to an accuracy of 20 millimetres.

Significant achievements and benefits

The construction of the main sewer was a combination of techniques. A DN400 steel casing was microtunnelled into position as a precision guide for the installation of a DN1500 steel casing using a 64” auger boring machine. This in turn allowed a DN1200 plastic lined RC pipe to be jacked into position while removing the DN1500 casing.

With sections of the collector sewer reaching 12 metres in depth, working in deep concrete caisson microtunnelling pits presented inherent risks in the access and egress of DM Civil personnel. To mitigate these risks, DM Civil designed and fabricated a fall arrest platform which was positioned at the point of entry into the caisson. A Pro-Man fall arrestor attached to the platform enabled personnel to be secured before entering into a high risk working area. This safety enhancement saw DM Civil as a finalist for the 2014 Work Safety Awards.

Along the collector sewer, there were eleven plastic lined, 1.2 metre square chambers up to 12 metres deep. Utilising DM Civil’s in-house concrete fabrication expertise, these units were able to be precast at the Maddington yard. This was a value adding innovation which allowed for cost savings to be passed on to the client.

HDD techniques were used to install a combined length of 1,090 metres through varying ground conditions of sand and limestone. This pipe route was adjacent to a newly constructed residential development with extensive landscaping. The technique permitted installation of pipe up to 10 metres deep with minimal disruption to residents. It modified the hydraulic design and obviated the need to install a discharge tower alongside the development further reducing the impact on existing areas.

The diversity of construction techniques available to DM Civil provides multiple options that can be offered. These options were used to ensure that Water Corporation was able to satisfy a demanding list of project imperatives, and demonstrated the position of DM Civil as a specialist contractor.