| DUSEL excavation would remove 1.5M tons of rock from Homestake |
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| Written by Wendy Pitlick |
| Tuesday, 22 June 2010 |
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Open cut considered as option for rock storage LEAD Current estimates say that if the deep underground science and engineering laboratory is built, contractors could excavate about 1.5 million tons of rock from the mine. That rock would fill the open cut up to the third bench from the bottom, but would be no higher than that, David Vardiman, DUSEL Project Engineer for Geotechnical Design and Excavation said. But with each bench about 80 feet from the next, spanning the circumference of the open cut, Vardiman said that’s still a lot of rock. Bill Roggenthen, co-principal investigator with the DUSEL team said estimates show that the open cut could hold between 100-150 million tons of rock. That makes DUSEL waste rock estimates of 1.5 million tons approximately 1 percent of the total capacity. Vardiman, whose primary job with the DUSEL project is to oversee contractors who are designing the excavation for the underground labs at the 4,850 and 7,400 levels, has a very delicate, complicated job. “This requires unique excavation procedures, ground support and very sophisticated design to make sure that those large caverns can be excavated in an economical manner, as well as in a manner that allows the campus to endure for its design life of 30 to 50 years,” he said. Vardiman said one of the largest DUSEL caverns for the project will be located at the 4,850-foot level. At about 180 feet in diameter, and about 272 feet high, the cavern would be large enough to house Mount Rushmore. The excavation project for the lab will include increasing the existing drifts both vertically and horizontally, as well as adding new drifts and caverns. The job is one that Vardiman is very excited about. A former Homestake employee for about 12 years, Vardiman did mapping, diamond drilling, grading and core logging for the drifts leading from the No. 6 winze to the 8,100-foot level. Back then, Vardiman said he did his work by the location of the ore. Today, his work is more about the best, most efficient way to build the underground lab. Currently, Vardiman said crews are already excavating space in the mine for the LUX (Large Underground Xenon) and the Majorana experiments. That rock, he said, is being stored in existing old drifts and old stopes on the 4,850-foot level. But, he said, there aren’t enough old drifts and stopes available to store the rock for the entire DUSEL construction project. “We don’t have enough access in old workings to accommodate (1.5 million tons),” he said. “So we’re looking at all of the other options.” While the open cut may be a viable option, it comes with its definite challenges, Vardiman said. “The question, of course, is how do you get it there so that it is not intrusive on the community,” he said. “There are other places being evaluated as well.” Bill Roggenthen, co-principal investigator for the DUSEL project said other options for rock storage include keeping it on the surface property or contracting with private companies to dispose of the rock. Another option for some of the smaller excavations, Roggenthen said, is to store the rock underground. “In fact, in the case of the deep levels that might actually be the plan because the amount of rock isn’t really that great for the smaller modules,” Roggenthen said. Though contracts to complete the preliminary design for the DUSEL are expected to be 90 percent complete in July, Roggenthen stressed that the preliminary design will only comprise 30 percent of the actual DUSEL design. That means that plans for such details as rock disposal and facility design are very preliminary, he said. The DUSEL team is expected to submit detailed preliminary design plans for the underground lab, as well as surface facility construction, to the National Science Board in December 2010. After that, the DUSEL team will participate in a series of reviews while the national board determines whether to move the project forward for funding requests. |
