The South Australian Water Corporation is constructing a 90 kilometre (56 mile) pipeline from Iron Knob to Kimba, on the upper Eyre Peninsula, to augment the water supply in the region.
The contracts were let to two contractors, Leed Engineering (Leed) and BJ Jarrad (Jarrad), to construct approximately 45 kilometres (28 miles) of the pipeline. Both contractors used new Vermeer trenchers, available from Vermeer Australia, to complete the project. The construction work commenced in May 2006. Both contractors completed the pipe laying in November 2006 and by January 2007, all hydrostatic testing was completed.
Jarrad have been long-term users of trenchers and have used the older Vermeer trencher for years. The Iron Knob/Kimba project commenced from the Kimba end, using a newly purchased Vermeer T755 trencher, which was bought especially for the project.
The new Vermeer T955 trencher was the first trencher used by Leeds, as their previous pipeline jobs were more suited to excavators.
The pipeline used 375mm (15 inch) DN ductile iron cement-lined (DICL) pipe and followed the path of the Eyre Highway, thereby simplifying site access but introducing traffic management issues.
The contractors’ scope of work covered trenching, laying pipe, backfilling and testing the completed pipeline. The trench was dug 750mm (30 inches) wide and to a depth of 1.4m (4.6 feet). TS4 sand was used to surround the pipe and provide a minimum cover of 150mm (6 inches). The trench spoil was then used for the remaining backfill material.
While digging conditions for the commencement of the Jarrad contract were good, the early part of the Leed contract was characterised by ironstone and quartz. Conditions improved toward Lake Gillies (where the contract sections met), but rock was also encountered 34 kilometres (21 miles) outside Iron Knob.
According to Leed, the new Vermeer T955 trencher was suitable for the project and the particular form of trenching.
Although a 10m wide (33 foot) corridor was allowed for the work, Jarrad worked within an eight metre wide (26 foot) corridor, to minimise environmental issues. Cleared vegetation was mulched and bagged to provide temporary support for the pipeline before it was laid in the ground. This was easier for the workers to handle than sandbags. The trencher towed a drag box to lay bedding sand for the pipe with a wheel loader feeding the box.
As part of pipe supplier Tyco Water’s specifications for ensuring that its DICL pipe was installed correctly in the ground to achieve its design life, the pipe was wrapped in Blueboss polyethylene sleeving and secured with strapping. Jarrad had a hairpin mandrel attachment built to Tyco’s design by Ottoway Engineering in Adelaide pipe to handle the pipe and mounted this to an excavator. The pipe was held on the mandrel, while the sleeving was placed on the pipe and then the mandrel was used to push the pipe home when joining the pipe sections.
An excavator followed this team and placed the pipe in the trench, and a truck fitted with a Flocon body and side conveyor trailed, which placed bedding material around the pipe. Where necessary a water cart was used to control dust and moisture for the compaction of the bedding material. Compaction was performed using a wheeled excavator with a vibratory plate compactor.
A grader then bladed the windrowed spoil back into the trench to complete the backfilling.
The Vermeer T755 trencher enabled faster trenching, of up to 160 meters an hour in good conditions. The trencher would complete its work and be parked each day for maintenance.
The abrasiveness of the soil was a major issue and Jarrad worked in collaboration with a local hardfacing specialist to find a method to protect the trencher. Jarrad undertook the step of rebuilding teeth with hardfacing and found that this increased the life of the teeth significantly. Hardfacing was also applied to the boom and wear plates.
In normal conditions, the new Vermeer T955 trencher was utilised to lay pipes between 800 and 1000 metres (2,625 and 3,281 feet) in a day.
Leed used similar methods to Jarrad in towing a drag box behind the trencher to place bedding sand. A full box could place around 30 meters (98 feet) of bedding, and in using a hairpin mandrel attachment on an excavator for placing pipe (this followed between 30 and 150 meters (98 and 492 feet) behind the trencher). A grader was also used for mixing and placing the backfill.