14 JUNE 2022 WorldWide Drilling Resource® O-Pile® Technology Used Successfully at the Island Mine Adapted from Information by Keller The Island Mine, owned and operated by Alamos Gold Inc., is an active underground gold mine located on the north shore of Lake Superior. It is also the site of Keller's first North American O-Pile® project. The mine achieved commercial gold production in 2007. Since then, production has grown significantly through ongoing exploration, and in 2019, rose to a record high of 154,400 ounces. One expansion was completed in 2018, with a second initiated in 2019. The second expansion phase required installation of a cut-off wall on the downstream side of an existing dam to allow for additional dam tailing deposits. Subsurface conditions consisted of 6.5 to 29.5 feet of sand and gravel till with cobbles, boulders, and flowing water conditions. Beneath this was granitic bedrock. Along with the flowing groundwater and challenging soil profile conditions, several other obstacles needed to be addressed to select the best method of cut-off construction. These included the requirement for a completely watertight cut-off and uncertain depth to the top of rock. Ledcor, the general contractor, had previously worked with Keller on a number of projects and was familiar with the company’s range of in-house solutions. Keller was invited to early discussions and provided information on several cut-off techniques, discussed anticipated constructability challenges and technical considerations, and addressed the time-sensitive aspect. With consideration of the challenges, Keller suggested O-Pile cut-off technology. O-Pile walls are relatively new to North America and consist of tightly interlocked pipe piles utilizing a mechanical “ball-and-socket” type connector to create a watertight cut-off. The wall can be readily embedded into the sound rock to complete the cut-off. Additionally, construction is rapid. Based on these characteristics, O-Pile technology was accepted by Ledcor and Alamos Gold, and Keller was retained for the work. Additional subsurface exploration was conducted along the dam to better determine the top of the rock so the pipe piles could be prefabricated off-site. A total of 68 interlocking pipe piles were installed. Each was 24-inch diameter, complete with ring bit, connectors, sealant, and tremie grout pipe. Interlocking pipe piles varied in length from 16.5 to 36 feet. A pile guide and template ensured verticality during installation, with additional post-installation verticality verification also performed. A full-time, on-site technician performed quality control for each installed interlocking pipe pile. Pre-and post-installation pump tests were conducted to confirm the adequacy of the cut-off wall. Keller crews worked six days a week for six straight weeks to complete the project safely and in a timely manner, allowing Alamos Gold to maintain its original production schedule. MIN
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