Success on the Denmark Pump-back Main project
Background of the works
DM Civil was tasked by the Water Corporation to urgently install a new PVC main from the Quickup Dam to the water treatment plant to provide drinking water for the township of Denmark. This project included clearing areas of state forest, a bore under the Denmark - Mt Barker Road, and installation of pipe under the Denmark River adjacent to the existing weir. Due to the design of the river crossing, the only way to ensure correct construction was to dam the flow of the river, and complete the installation via open excavation. The contract was awarded and commenced in late April. Constructing a pipeline in the region at this time of year was not favourable due to the high probability of wet weather, however DM Civil was up for the challenge.
The Denmark River crossing was the riskiest and most significant section of the job. Due to the high annual precipitation in the area, DM Civil had limited time to complete the works before the winter rains would make the area impassable, however the completion date for the main was also before winter to ensure ongoing water supply for the Denmark area. Therefore, failure to complete this section of works would bring the whole project to a halt.
In order to complete this mammoth task within the small window of time available, the crew led by Paul Dougan, sprang into action and acquired three 6-inch dewatering pumps, installed 2 x 100mm syphons over the dam wall and opened the weir scour to create a bypass system of 900 litres a second around the work area. This helped reduce the weir water level, providing the crews a buffer zone before overflow. If the weir overflowed, this would effectively flood the worksite. This system ran 24 hours a day and required a night shift crew to monitor the area as any hose breakages had the potential to further waterlog our clay soil work space, making the area inaccessible to machinery.
After 3 days of pump operation, the weir had dropped by 600mm and rock breaking began in the granite river bed. This provided the pipe with sufficient embedment and protection from any water surge over the weir in the future. Immediately behind the rock breaking was a team installing pipe cradles, followed by steel fixers completing the pipe encasement and installing the polyethylene pipe which was anchored to the bedrock. Once the formwork was finalised, preparation for the concrete pour began.
The order for concrete was placed with ominous looking weather and reports that Mt Barker and Albany were about to be hit with a storm. Once the first of five trucks had been ordered, we were informed that power had gone out in Denmark and the concrete would need to be batched in Albany. This created an additional 50 minutes of waiting time for the second truck, still with the impending storm.
Luckily the storm held until Sunday morning and the concrete was poured with the final truck leaving at approximately 8:30pm Saturday night. The personnel involved knew the importance of completing these works and is testament to the dedication of DM Civil employees to the company.
It was a massive effort for all involved, with special mention to leading hands Dave Parker and William Brace and their respective crews. The Water Corporation has mentioned numerous times to the team that we greatly exceeded their expectations and completed “mission impossible” 3 days ahead of schedule, and about 3 hours ahead of the rain.