Sydney Water, in common with other major water authorities, has a number of critical sewers of oviform shape. While this egg shape has the advantage of providing a self-cleaning velocity at low flows, the same shape makes it very difficult to design and install a lining that will restore structural strength to the sewer without loss of flow capacity.

The awarded contract, Sewer/Stormwater Rehabilitation Program – SR2009-2012 Package 6 Bundle 1, will involve relining pipes that are 990 mm x 660 mm in size.

When completed, this work will address sewer surcharges, infiltration and exfiltration issues and help to overcome environmental damage and public health implications. All job sites involve high difficulty in terms of access to the sewer maintenance holes. The work will return the respective sewer assets to their designed level of performance.

CIPP chosen for structural lining

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Kembla’s Enviroliner system is a cured-in-place pipe (CIPP) method for the renovation of pipelines by installing a resin-impregnated flexible tube that is inverted into the existing conduit using hydrostatic pressure.

The tube is cured to a hardened state while held in intimate contact with the conduit. CIPP linings are tailor-made to suit the circumference of the pipe and because they are inserted in a softened state they take the shape of the host pipe. This makes CIPP ideal for non-circular shapes, such as oviform.

The system was tried and tested by Sydney Water on two critical applications before the calling of tenders. The capability to successfully line deteriorated oviform pipes including bends had been demonstrated.

Below are two case studies that highlight the difficult nature of the work encountered in the Bundle 1 program.

Roseville case study

Roseville involved 225 m of 533 mm x 406 mm oviform sewer main that was located along Roseville Creek with no vehicular access to the access chambers. The location was classified as environmentally sensitive Category B site.

There were a number of issues including:

  • Large storm water culvert discharged into the creek just upstream from the first access chamber and a severe thunderstorm just before the start of work knocked several trees down, one of which sheared off the top of the access chamber;
  • Restricted access to the nearest chamber required locating a crane that had the necessary reach without closing down the access road for residents; and,
  • The only practical solution was to line the entire 225 m length in a single installation.

Installation

A 22 m long access platform was erected from the roadway through native bush over the creek to the top of the access chamber.

There were over 400 customer letters hand delivered and 50 home plans were done with local residents. Home plans are prepared for each property directly affected by the work, be it an access chamber located in the backyard or a truck parked in front of the property. Each resident is taken on a personal walk through of the planned work by one of Kembla’s Community Relations Officers so that they understand the nature of the work and the impact it will have on them.

The entire installation was completed using a continuous rotating shift over a number of days that enabled one single lining installation.

The structural lining installed by Kembla has provided a minimum of at least another 50 years design life to this critical asset and the work was completed without any damage to the vegetation in “Little Digger Park” and without a single complaint from local residents.

Point Piper case study

The Point Piper project relined 835 m of 406 mm x 533 mm oviform, involving six separate installations.

Challenges on the Point Piper included:

  • All the sewers being rehabilitated were located adjacent to New South Head Road, an RTA controlled main road;
  • Point Piper is a very affluent suburb adjacent to the Sydney Harbour foreshore with many high-density blocks of residential units;
  • One length of the sewer was located underneath Woollahra Council Chambers and vehicle access was not possible to over 50 per cent of the access chambers; and,
  • The sewers were found to be very dirty and about twelve tonnes of silt and debris was removed during cleaning operations prior to lining. In some areas up to 150 mm of silt was found in the invert of the sewers.

Installation

There were over 500 letters hand delivered in the area and over 60 individual home plans were prepared and discussed with residents.

During the installation only five residents were temporarily relocated into hotels because of restricted access situations. Thanks to the use of Trenchless Technology, only one day’s relocation was necessary.

In addition, 20 alternate parking arrangements were made for affected residents.

More than five months of lengthy consultation was carried out with the RTA and local council in order to reach agreement on a date to shut down the east-bound lanes of New South Head Road.

Six individual flow management plans were prepared, each with unique challenges involving various pumping station shutdowns, among other issues.

Summary

There can be no denying from the photographs that this pipeline rehabilitation work did involve some level of disruption to local residents. However, careful preparation of site specific environmental plans, flow management plans, traffic management plans and individual personal consultation with affected residents kept this disruption to a minimum.

Dig up and relay of a new sewer at these locations was simply not an option. Trenchless Technology was the only possible solution and by coupling experience with thorough planning Kembla has been able to successfully complete this difficult and critical work.