An Investigation of the Mechanical and Hydrologic Behavior of Tuff Fractures Under Saturated Conditionsby C. F. Voss, Pacific Northwest Lab, United States,
L. R. Shotwell, Pacific Northwest Lab, United States,
Abstract: The mechanical and hydrologic behavior of natural-fractures in a partially welded tuff rock were investigated. Tuff cores, each containing part of the same natural fracture oriented subparallel to the core axis, were subjected to a range of stress and hydraulic gradients while simultaneously monitoring changes in the fracture aperture and volumetric flow rate. The fractures were tested in three configurations: intact, mated, and offset. Fracture deformation was nonlinear over the stress range tested with permanent deformation and hysteresis occurring with each loading cycle. The offset samples had larger permanent deformation and significantly reduced normal stiffness at lower stress levels. The cubic flow law appears to be valid for the relatively undisturbed (mated) tuff fractures at the scale tested. The cubic law did not explain the observed hydraulic behavior of the offset fractures.
Subject Headings: Hydraulic fracturing | Rock mechanics | Deformation (mechanics) | Cracking | Hydrologic properties | Mechanical properties | Welding
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