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"Extract from paper delivered by David Heape and Andy Krumins of Brisbane Water and Brian Fenton of Tyco Water at Pipes Wagga 2001" WHEN Brisbane Water chose to reline 10k of large diameter sewer pressure mains a year ago rather than replace the existing pipe, it was the first time that this had been done in Australia. The main sewer line services 60 percent of the city and gravitates to the 8000 l/sec Eagle Farm pumping station, where it travels through two large rising mains to the Luggage Point tertiary treatment plant, where it is treated and discharged into the Brisbane River. The Eagle Farm Rising Main system is 9.5k long, and comprises one 1370mm main extending the entire distance and one 1840mm main connecting to two 1275mm concrete mains at Serpentine Road. The 1370mm main provides a significant portion of the peak wet weather capacity, and redundant capacity during dry weather to allow inspection and maintenance on the 1840mm main. As it carries over 50 percent of the capacity from Eagle Farm to Luggage Point it must be able to operate reliably without bursts, and accommodate anticipated future flow increases. This main was constructed in 1974, with welded ball & socket joint pipe to Serpentine Road, and rubber ring jointed pipe from Serpentine Road to Luggage Point. There was a pattern of increasing failures from 1990, resulting in significant discharge incidents. An internal inspection of nine percent of the pipe in 1994 showed significant erosion in the inverts of all joints and in the invert and side wall of bends. Testing showed that in some areas the original 10mm wall thickness had eroded to less than 2mm. There were also problems with the external coating of the pipe, with evidence of moisture between the coating and steel pipe. Over the past few years some external patches were applied, some joints were replaced, some areas had cement lining restored with gunite and 2k was relined with u-PVC liner. It was originally proposed that the main be replaced, but as the cost of $30m was unacceptable to the council the hitherto unattempted solution of relining the remaining area (7.6k) at a cost of $10m was explored, and this was done in late 2000. Tyco Water’s Panel Lok 3, a 300mm wide strip of extruded uPVC with a flat smooth inner surface and ‘T’ profile ribs on the exterior was chosen. The main reasons were its excellent resistance to chemical degradation in a sewage environment, its superior abrasion resistance, its low surface friction coefficient (for improved flow), the relatively low cost of the base material and its ready availability. The material is handled in 50m coils. A coil is placed over the pipeline access, unwound from the centre of the coil and pulled into the pipe and up to the point where the pipeline is to be replaced. The liner is spirally wound manually to rest against the inside of the existing pipe. Male and female clips lock the strip to form an inner pipe. New strips can be butt-joined and bonded to the previous strip to continue the process. A grout (usually a blend of cement, flyash and/or sand and water) is pumped into the annular space between the original pipe and the liner, bonding the two together and transferring shear stresses between the inner and outer pipe components. Pressure grouting also fills cracks and voids in the original pipe, enhancing its structural capacity. Tyco Water supplied a proprietary rubber joint sealing system known as AMEX 10 to protect the expansion joints of the pipe from internal attack. The rubber seal sits flush with the liner and is held in place by steel bands, preventing hydraulic loss. Inspections of the 2k of original relining done some five years prior to the main project revealed no deterioration or loss of liner thickness. The only repairs required were to an older design of grout plug and joining strip, and these were quickly repaired. The council expects a minimum 30 year life from the relined pipe, with minimal requirement for repairs.
Article published with permission from Greg Keane of Construction Contractor.
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