Chichester trunk main diversion, Maitland, NSW, Australia
As part of a planned mine expansion, Donaldson Coal Mine proposed to construct a diversion for the Chichester Trunk Gravity Main (CTGM), a publicly-owned asset that supplies water to Newcastle. Originally constructed pre-WW1, and partially rebuilt in the 1960s, the CTGM is a gravitation main comprising a 914 mm (36”) diameter mild steel welded pipe with cement lining. It is situated above ground supported on concrete saddles at approximately 7.6 m centres and thrust/restraining blocks at 45 to 75 m intervals.
PSM was engaged to construct a diversion to allow mine expansion. The project also incorporated additional hydraulic infrastructure to provide greater flexibility for Hunter Valley Water Corporation in the supply of water to Maitland and Newcastle.
A high-value asset owned by the Hunter Water Corporation (NSW), this critical public water supply pipeline from the Chichester Dam supplies the Stony Pinch Reservoir and, in turn, the city of Newcastle. Loss of operation for periods greater than 24 hours can result in loss of service.
Donaldson aimed to complete the diversion construction and the cut-in before the start of the high-demand period. To avoid interruption to public water supply the maximum allowed cut-in period could not exceed 24 hours.
APPROACH AND INNOVATION
PSM’s tailored approach included rigorous assessment of technical detail to facilitate construction and interactions between the asset owner, designer, contractor and client.
Limiting time variations to extensions for wet weather and changes requested by the asset owner resulted in no need to enact a liquidated damages clause. Cost variations were limited to changes requested by the asset owner and stabilisation costs for a road crossing costed at a schedule of rates in the tender.
The cut-in date before the high-demand season and within the 24-hour works period was achieved without compromising quality. There was minimal interruption to public water supply.