When unexpected ground conditions were encountered at the mine at the proposed site for the expansion of the tailings dam, a 40m (131 ft) long cut-off wall was required.
Various solutions were considered but with several metres of thick sand and gravel till, cobbles, boulders underlaid by bedrock, and flowing water conditions, O-piles were chosen as the preferred solution.
Other benefits of using O-piles include rapid construction using a rotary percussive drilling process in a single pass and a watertight seal using mechanical interlocks. Like sheet piles, the O-pile system creates a cut-off wall and can be used for excavation support. However, while sheet piles would refuse to drive through rock and boulders, a down-the-hole hammer is used to advance the O-pile through these conditions.
Keller crews installed 68 O-piles with lengths varying from 5m (16.4ft) to 11m (36.08ft) as required. O-piles were 610mm (2ft) in diameter.
Project manager Anojan Siva said: "We were involved early on in the process to explain the pros and cons of several potential cut-off wall techniques. We were able to discuss and resolve anticipated constructability challenges, technical considerations, and address the time-sensitive requirements for this critical project."
During construction, Keller provided high calibre experienced personnel working six days a week for six weeks. "We were able to provide a high-quality solution using a pile guide/template to ensure pile location and verticality; and performed continuous inspection and monitoring of all activities," Siva said. The project was completed on schedule and Keller has already planned future projects using O-pile technology.
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