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Published 1988 | Published
Book Section - Chapter Open

Stress Field at Yucca Mountain, Nevada

Abstract

Hydraulic fracturing stress measurements performed in four holes (USW G-1, USW G-2, USW G-3, and Ue25P1) indicate that at Yucca Mountain, the least horizontal stress S_h is less than the vertical stress S_v. Values of the greatest horizontal stress S_H are intermediate between S_h and S_v, corresponding to a normal faulting regime with values of Φ = (S_H-S_h)/(S_v-S_h) between 0.25 and 0.7. Drilling-induced hydraulic fractures seen on borehole televiewer logs indicate an S_h direction of N. 60° W. to N. 65° W. in USW G-1, USW G-2, and USW G-3. The same S_h direction is inferred from breakout orientations in USW G-2 and Ue25P1. The S_h values in the upper parts of the three USW G holes are less than the pressure of a column of water filling the borehole to the surface. Thus, the long drilling-induced hydraulic fractures in the shallow parts of these holes could have been formed in attempts to maintain circulation during drilling. These low S_h values may be intimately related to the low water table and fracture-dominated hydrology of Yucca Mountain.

Additional Information

© 1988 USGS. We thank W.F. Brace, Art McGarr, and Mary Lou Zoback for helpful comments. Hans Swolfs' suggestions were also much appreciated, although he does not endorse all of our conclusions. The field measurements were performed in cooperation with the Nevada Operations Office of the U.S. Department of Energy under interagency agreement DE-AI08-78ET44802. J .M. Stock thanks the Fannie and John Hertz Foundation for supporting her graduate work at the Massachusetts Institute of Technology, during which time this paper was completed.

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August 19, 2023
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January 13, 2024