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RESOLUTION COPPER High-pressure Couplings Solve Deep Mining Challenges at Resolution Project By Marc Carriere lating groundwater. Below that zone, tem- perature almost always increases with depth. However, the rate of increase with depth (geothermal gradient) varies consid- erably with both tectonic setting and the thermal properties of the rock. At the Resolution Project, temperatures can reach 130°F to 140°F at current depths. To keep workers comfortable, cool- ing in the form of a chilled water line was necessary. Of course, running water to a depth of several thousand ft—and an even- tual depth of 7,000 ft—presents several challenges. With plans to sink exploratory shafts 7,000 ft, Resolution Copper Mining needed a pipe-joining solution capable of handling the immense head and end-loads. As mines reach increasingly greater depths, piping water to and from the sur- face becomes ever more challenging. Mining contractor Cementation faced this obstacle when designing a chilled water line for the Resolution Project, located in the historic Pioneer Mining District just east of Superior, Arizona. With plans to sink exploratory shafts to 7,000 ft, Resolution Copper Mining needed a pipe- joining solution capable of handling the immense head and end loads, while offer- ing flexibility to accommodate expansion and contraction. Victaulic provided a solu- tion that met these specifications, and also reduced installation time and total installed costs. The Resolution Project, 55% owned by Resolution Copper Co., a Rio Tinto plc sub- sidiary, and 45% BHP Copper, is currently in the pre-feasibility phase. Exploration conducted in 2001-2003 revealed a large copper ore body more than a mile below the surface—a deposit that could prove to be one of the largest copper ore bodies ever found in North America, and possibly the world. In 2010, Rio Tinto reported an inferred resource of 1.624 billion metric tons (mt), containing 1.47% copper and 0.037% molybdenum—an increase over its 2008 announcement of 1.34 billion mt. If addi- 108 E&MJ; • JUNE 2012 tional drilling verifies these numbers, a mine of this size would be capable of pro- ducing 25% of expected future U.S. cop- per demand over several decades. Production via panel caving, which is like- ly to begin in 2020 if evaluation and feasi- bility studies, and a land exchange are suc- cessfully completed, is predicted to span 40 years. In addition to technical and environ- mental studies, the work scheduled for the next several years includes dewatering Shaft No. 9 of the former Magma mine, which was shut down in the late 1990s, and sinking a new exploratory shaft, No. 10, to 7,000 ft below the surface. As of April 2012, Shaft No. 10 had reached a depth of about 5,500 ft, with operations progressing at about 10 ft per day under 24-hour operations. The Challenge As mining operations progress deeper, the temperature of the rock increases. According to a paper by T. Payne and R. Mitra of the University of New South Wales, Sydney, Australia, rock within 50 m (~164 ft) of the earth's surface maintains a temperature equal to that of the average air temperature. Between 50 m and 100 m (~164 ft to 328 ft), the gradient varies based on atmospheric changes and circu- The first challenge was designing a pip- ing system capable of withstanding the head and end-load of the vertical installa- tion. The piping system had to withstand a maximum working pressure of 3,500 psi. In addition, piping hung vertically to such depths creates a tremendous amount of end-load, so the system would have to be capable of withstanding the load, ideally without extra pipe supports. The second challenge was accommo- dating the temperature variations produced by the chilled water running into a hot shaft, and the resulting expansion and con- traction of the piping system. The initial plan for the chilled water line was to join the 8-in. schedule 80 pipe with 900-lb flanges. (As the depth of the shaft increases, Schedule 120 and Schedule 160 pipe will be used.) However, flanges would not provide the flexibility required to accommodate the temperature variation. As a result, Cementation sought alternatives. Cementation evaluated two different joining systems; the first was a non- restrained flexible coupling, the second was the Victaulic Style 808 double-grooved coupling. Both pipe-joining methods had the ability to accommodate the high pres- sure, expansion and contraction, but the 808 was also a restrained joint. The other option would have required restraint sys- tems on either side of the piping, increas- ing the installation time and cost. The Solution Ultimately, Cementation chose the Victaulic 808 high-pressure coupling. It is www.e-mj.com