Lucas’ HDD teams have established a new record with the completion of two 2,400 m drills for Sydney Water’s Upper Blue Mountains Sewerage Scheme as part of the Priority Sewerage Program (PSP) Alliance.
The two HDPE pipes, a DN450 and a DN225, will connect sewers in Mount Victoria, Medlow Bath and Blackheath to the main sewer tunnel in North Katoomba. This will carry the sewage 39km to Winmalee Sewage Treatment Plant for tertiary treatment and disinfection.
The bores travel deep beneath a hanging swamp and approximately 60 m below the concrete-cored embankment wall of the Upper Cascade Dam and the area’s water table. At their deepest, the pipes are 180 m below the surface. They intersect the 3 m sewer tunnel approximately 60 m below ground from different directions.
Lucas’ DD1080 rig was used to drill the bores. The larger hole is 660 mm and was drilled and reamed in two passes. The smaller hole was 311 mm diameter and was drilled in a single pass.
In all, some 90 km of drill pipe was tripped during the project. Mud pumping duties were handled by two Gardner Denver PZ8s.
Geology was sandstone with mudstone and ironstone bands, which made holding inclination tricky as the drillhead traversed the ironstone. The two pipes were installed by forward thrusting using a 30 tonne excavator. Installation load for the DN450 pipe was 12.5 tonnes – exactly as Lucas’ engineers had modelled. Load for the DN225 pipe was 1.8 tonnes. Installing this required close attention to mud condition to ensure the viscosity was optimum – “It was like pushing a wet noodle through a straw” according to project manager Daniel Sweeting.
The engineering of the pipe installation was very exacting. Had the friction calculation been out by 0.02, the pipe simply wouldn’t have gone in. As it was, Lucas’ engineering and steering was exact, with both pipes going in as predicted, meeting the sewer tunnel well within the 1 m target zone.
With the nearest resident 450 m away, noise wasn’t as critical as some other projects. The company’s acoustic barriers ensured noise never rose above the ambient for locals. The site is within the Katoomba Special Area, bordering the Sydney Catchment Authority’s land around the Cascade Dams, so environmental controls were stringent. Lucas was audited three times by external environment auditor – scoring 98 per cent twice and 99 per cent on the third inspection.
Work commenced on the 5 March and proceeded 24 hours a day, seven days a week until installation was completed on the 28 July. As we go to press, pigging has just been completed, confirming that all is well with the two pipes.