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Preliminary assessment of in-situ geomechanical characteristics in drill hole USW G-1, Yucca Mountain, Nevada

Open-File Report 83-401

By:
,

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Abstract

Observations made during drilling and subsequent testing of the USW G-1 drill hole, Yucca Mountain, Nevada, provide qualitative insights into the in- situ geomechanical characteristics of the layered tuff units penetrated by the hole. Substantial drilling-fluid losses, and the occurrence of drilling-induced fracturing, are understandable in terms of the low, minimum horizontal stress magnitudes interpreted from six hydraulic-fracturing stress measurements conducted between hole depths of 640 and 1,300 meters. Although not confirmed directly by the hydraulic-fracturing data, other observations suggest that the minimum stress magnitudes in the more densely welded and brittle tuff layers may be even smaller than in the less welded and more ductile rocks. Stress-induced borehole ellipticity observed along most of the length of USW G-1 indicates that the horizontal stress components are not equal, and that the concentration of these stresses around the hole is sufficient to locally exceed the yield strength of the rock. The low, minimum horizontal stress magnitudes, perhaps variable with lithology, and the indications from borehole ellipticity of a high in-situ stress/strength ratio, indicate the need for further studies to characterize the structural and geomechanical properties of the rocks at depth in Yucca Mountain.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Preliminary assessment of in-situ geomechanical characteristics in drill hole USW G-1, Yucca Mountain, Nevada
Series title:
Open-File Report
Series number:
83-401
Edition:
-
Year Published:
1983
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
ii, 20 p. :ill., maps ;28 cm.