Trenchless Technologies and Helicopters

OVERVIEW

As part of Sydney Water Corporation’s (SWC) ongoing systematic inspections of sewer lines across Sydney; structural, service, exfiltration and infiltration problems have been identified in various locations within the sewerage system.  In response, SWC initiated the Sewer Rehabilitation Programme (SRP) 2005-06, with the objective of rehabilitating these sewer lines to their original condition and performance levels.

Sydney Water commissioned Kembla Watertech Pty. Ltd. (Kembla) to undertake remediation works of many of these deteriorated pipes a number of which are located in areas identified by Sydney Water as being environmentally sensitive.  All worksites under the SRP contract have been divided into two categories A and B.  Category B sites are environmentally sensitive sites including National Parks, urban bushland, heritage conservation sites etc. and SWC requires that site specific environment impact mitigation measures be developed for these sites.  Kembla prepared a Construction Environmental Management Plan (EMP) to ensure that all potential environmental impacts that could reasonably be expected to occur during the proposed works are minimized and fall within acceptable and agreed limits. As part of this proactive approach to environmental management one Category B site in particular at Truscott Place Killara (Sydney) was identified as potentially a very difficult situation.

LOCATION

The site works for this 225mm diameter sewer is located within a gully of Garigal National Park which follows Gordon Creek and is some 300m from the nearest vehicular access point. An unsealed narrow path traverses the steep gully side before crossing the creek and roughly following the line of the sewer and it was considered that with heavy traffic the path would become slippery and possibly unstable.

EXISTING ENVIRONMENT

  • The EMP identified the following aspects:
    All manholes are located within 25m of a natural waterway and within dense bushland that is relatively undisturbed.
  • Two manholes are located within the watercourse itself.
  • The odour of sewage at the site suggested that water quality was currently being impacted by the sewer line and confirmed the need for urgent rehabilitation.
  • Access is via a steep embankment leading off Truscott Place.
  • The clearing of vegetation along the limited access could increase the erosive potential of the site.
  • Due to the relatively undisturbed condition of the site, the presence of a waterway and the presence of sandstone outcrops, a search of the Aboriginal Heritage Sites register was undertaken and identified an open camp site and an axe grinding groove some 250m from the site.
  • Access to the manholes would be restricted to foot access.
  • Access during wet weather would not be permitted.

PROPOSED REHABILITATION

The 225mm diameter size of this sewer, makes it ideal for Kembla’s Ex lining method. This No Dig technology involves a pvc pipe which is pulled into the sewer in a folded shape and then reshaped (‘formed”) into a circular pipe by the application of heat and pressure which moulds the liner to the host pipe surface.

The solid wall structural Ex pipe is tight fitting to the existing sewer and is joint free for its entire length.

While it is possible to position the steam boiler unit some distance from a site and simply pump the steam through a small pipe, it is necessary to position the coil of Ex lining and the pulling winch at the manholes.

The critical focus of the project management team became how to transport this equipment and material to the site given the potential impacts and associated safeguards identified by the EMP.

A HELICOPTER !

Because of environmental and safety concerns associated with access to this site, Kembla had a meeting with all stakeholders and proposed the use of a helicopter. Kembla had determined that it was possible to use a helicopter to pick up the basic materials and equipment from a nearby reserve and drop these directly at the appropriate sewer access chambers.

While at first seeming an “extreme” solution, after careful planning and cooperation between SWC and Kembla personnel this option proved to be more than a feasible solution. It solved all the concerns raised in the EMP over safe access and environmental protection, however, it did raise other issues. Kembla issued a revised work method statement specifically addressing the use of the helicopter on this project.

Following SWC approval to proceed, a Works Certificate was obtained from the NSW National Parks and Wildlife Service and then a Landing Strip Permit from Ku-ring-gai Council. The landing permit set aside a specific area on a nearby oval as shown in the sketch.

Once all safety procedures were in place and the helicopter sub contractor had obtained the FCA penetration work permit the work was carried out with clockwork precision during late November. The helicopter picked up the materials and equipment in a series of lifts from the designated loading zone and lifted these into the dense bushland where Kembla personnel were waiting to set it up.

The lining work was completed quickly and without any safety or environmental incident. The helicopter then returned to lift out the equipment and the National Park was left untouched.