ABSTRACT

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The proposed research is directed towards the preparation of a Preliminary Design Report for an NSF Major Research Equipment and Facility Construction (MREFC) project: The Deep Underground Science and Engineering Laboratory (DUSEL) at the former Homestake mine in South Dakota.

Intellectual Merit: This award will create carefully controlled faults at scales of 1-100 meters using thermal techniques to modify in situ stresses to the point where the rock fails in shear. These experiments will extend experiments on fault nucleation and growth to length scales 2-3 orders of magnitude greater than are currently possible in the laboratory. The experiments would be done at depths where the modified in situ stresses are sufficient to drive faulting, obviating the need for large, expensive loading frames. DUSEL Homestake presents an opportunity to conduct a unique experimental program by providing access to locations with vertical stresses as large as 60 MPa (down to 2400 meter depth), more than sufficient to create faults. It also allows facilities at different depths, permitting experiments to be conducted under different stress levels. These proposed experiments require a facility providing access to large rock volumes in the deep subsurface in a controlled setting, and one where interdisciplinary collaborations are encouraged; all the conditions are met at DUSEL Homestake. The ultimate scientific objective of this research is to substantially elevate understanding of faulting processes in crystalline rock, with particular emphasis on how faults are initiated and grow through intact rock. Another important objective is to observe and characterize the reactivation of a natural, existing fault. Both can be done at Homestake. The experimental suite we propose is motivated by a fundamental need across geosciences to advance the understanding of how rocks fail by fracturing. The experiment responds specifically to ideas in Deep Science, and to guidance and experiments in the DUSEL S1 Technical Report, and it is motivated by the Induced Fracture and Deformation Processes Laboratory in EarthLab.

Broader Impacts: Other experiments outside the field of rock mechanics will benefit from, and can accompany, the proposed experiments. The experiments will address formation of shear fractures in previously intact rock, slip on pre-existing joints, fault gouge formation, the influence of fault gouge on fault reactivation, and the evolution of fault permeability. It will further understanding of hydraulic fracturing, how fracture energy and rock strength scale with size, and how microbial systems exploit fractures. The results of the research will have direct applications for the production of geothermal energy and hydrocarbons, as well as the storage of waste and environmental remediation in the subsurface. Since the research is so highly cross-disciplinary, it will provide a rich environment for fostering new ideas among existing and future generations of scientists and engineers.

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