The Deep Underground Science and Engineering Laboratory (http://www.dusel.org) at Homestake gold mine in South Dakota is posing technical challenges far ahead of the actual experiments to be performed there. In particular, the mine itself must be prepared to ensure a safe as well as scientifically interesting work environment. Research in many scientific disciplines is being undertaken at this facility including Astrophysics, Geoscience, Microbiology and investigations of future technologies such as CO2 Sequestration.

Why perform experiments 8,000 feet underground? Because the mass of rock shields astrophysics experiments from cosmic interference. If you want to learn more about pioneering work in neutrino detection, you’ll find fascinating details here: www.bnl.gov/bnlweb/raydavis/research.htm.

Professor Herb Wang of the University of Wisconsin leads a team of geoscientists and engineers (GEOX) who are relying on fiber optic sensing systems to measure movement of the rock structures. The GEOX research is sponsored by the Geomechanics Program of the National Science Foundation. GEOX’s charter is clear: “The objective of GEOXTM is to understand the mechanical response of rock masses to loading for spatial scales from centimeters to kilometers and for time scales from milliseconds to decades by installing the world’s largest and deepest underground network of fiber optic strain and temperature sensors and tiltmeters.” One advantage of the fiber optic sensing technology is that not only is science being performed but safety and structural health monitoring of these very large structures can be realized also. The focus of the safety assurance work is to understand rock-mass deformation resulting from dewatering of the old mine passages followed by excavation of giant caverns that will house the experiments.

For example, meter long FBG based strain gages are mounted in threes to sense rock shifts in X, Y and Z axes in critical locations. Just last week, the GEOX team was working with hydraulic jacks in the mine to load the rock mass and study its response.

JoAnn Gage, a PhD candidate at the University of Wisconsin and key member of the GEOX team, has invented special “strain strips” that combine six strain and six temperature sensors and are grouted in boreholes in the rock.

The motivation for using fiber optic measurement techniques, rather than conventional electrical gages, is that fiber optic methods (including fiber Bragg gratings, Raman, and Brillioun) can address the wide range of measurement scales, i.e., centimeters to kilometers and milliseconds to decades.

Herb Wang sums it up nicely. “Fiber-optic sensors have the versatility and stability to extend our understanding of how rock masses deform. We were successful in this work because we received extensive technical support from Alan Turner and the entire Micron Optics organization.”

Alan Turner,
Micron Optics Sales

ETA: If you want to read more on SUSEL, you can purchase “Fiber Optic Strain And Temperature Monitoring In Crystalline Rock At the Sanford Underground Science And Engineering Laboratory (SUSEL), Lead, South Dakota” by Dr. Gage, et al. which was presented at the 44th U.S. Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium in 2010.