The New Street sewerage pumping station is located in the heart of Frankston on the Mornington Peninsula. The station is responsible for transferring up to 6 million litres of effluent daily and services a huge catchment of nearly 140,000 properties, also receiving flows from an additional eight pumping stations.

The 450 mm New Street rising main was constructed in 1975 by use of cast iron cement lined pipe and, after several failures, the first section was replaced some 8 years ago. The remaining section of rising main came up for renewal last year and was earmarked to be replaced due to concerns of failures occurring under the Frankston-Caulfield railway line and the Frankston Freeway which would result in an unprecedented environmental and social impact on the immediate and surrounding areas including the Port Phillip Bay region. This concern is elevated due to the fact that these major crossings were not sleaved during the original construction of the existing rising main.

The choice of an adequate rehabilitation system depended upon the performance parameters which the sewer rising main failed to meet and why the failures occurred. Consequently the following main design criteria were applied:

1. Condition of the existing pipeline 2. Technical aspects 3. Hydraulic aspects 4. Structural aspects 5. Environmental/social impacts

All technical and influencing issues were taken into account and studied carefully before selection of the most appropriate rehabilitation technique was done in accordance with cost effectiveness, quality and time constrains.

Several options were considered to replace this section of main and upon completion of a feasibility study it was decided that a combination of conventional and trenchless construction methods would be undertaken, along with 600 m of close-fit rehabilitation using the revolutionary ‘compact pipe’ technique. This system provides the old existing pipeline with a new, close-fitting pipe inside, thus taking over the function and structural integrity of the asset. The pipe is made from high quality polyethylene material and supplied in continuous length that is wound on a sturdy metal drum. The pipe is folded along its length into a C-shape and can therefore easily be inserted into the host pipe as the diameter is reduced by over 30 per cent. The flexibility of PE also allows for pulling the pipe around bends and keeping the insertion access area to a small footprint with least or no excavation.

Once insertion is complete, the compact pipe is reversed by use of steam and pressure. Due to the ‘memory effect’ of PE, the pipe regains its original, round shape. The pressurised air during the cooling process assures that the liner is brought in close contact with the inner wall of the old pipe. The result of this close-fit lining is a structurally, independent pipe with the quality and durability of a newly-installed pipe. The reduced cross-section and slight loss of inner diameter is at least compensated due to absence of obstructions and better flow characteristics. The long term internal pressure resistance for design life of 50 years at a 20°C minimum, when made in PE100 for SDR26, is 6.4 bar.

This project was carried out by ‘us’ - Utility Services and provided a cost saving to South East Water of close to $1 million, where the indicative price of the cheapest alternate option was quoted at $2.3 million.

To undertake these works, a 700 mm sleave bore was launched to house the rising main under the Frankston-Dandenong Rd and the adjoining railway line. The remaining section was rehabilitated using 450 mm compact pipe. In order to reline the existing section of rising main a temporary bypass pipeline was required to divert the flows from the pumping station around the existing main which allowed the relining works to proceed. As the New Street pumping station already runs at capacity, the bypass pipeline could not be downsized and had to be able to handle the flows currently transferred by the existing main. The two shutdowns of the main to connect the bypass and reconnect the rising main required an enormous operation, and saw the New Street pumping station flows transferred to another catchment using several eductor trucks capable of moving up to 28,000 litres of wastewater at any given time.

The existing rising main is located in a very dense area of Frankston and runs under several busy roads including the Frankston Freeway, along the local shopping precinct and under the railway line. To construct the 500 mm polyethylene bypass pipeline a large section of the pipeline was located in a 1,500 mm stormwater drain which passes under the freeway and along the busy Skye Road. By locating the bypass in the drain it minimised any impact on the greater public, surrounding areas and traffic flow.

In order to undertake these works, several authorities including VicRoads, City of Frankston, Melbourne Water and the EPA were heavily involved to ensure all risks associated with the works were mitigated.

To construct the bypass a specialised polyethylene welding unit was imported from Germany to fabricate the many bends necessary to erect the pipeline both above and below the surface.

In total the project took five months to complete and came in under budget and without incident. The actual rehabilitation work on-site was done in 35 days. This project was the largest rehabilitation project with compact pipe in Australia so far and will provide South East Water with an integral and reliable asset for many years to come.