Fracture Deformation Measurements in the Large Block Test

Fracture deformations were measured in a 3m x 3m x 4.5m block of Topopah Spring tuff as part of a larger effort to characterize coupled thermal-hydrologic-mechanical-chemical processes in an isolated rock mass subjected to a one-dimensional thermal gradient. The fracture deformations were measured in three orthogonal directions at 17 points on the vertical faces of the block over a time span of 19 months. Eight fractures, including a major sub-horizontal fracture near the top of the block and five large, sub-vertical fractures, were selected for study. The data provide point measurements of apparent aperture change and slip motions parallel and perpendicular to the block faces. The fracture aperture and slip motions, though only a few tenths of a millimeter, form a significant portion of the total block deformation. The data reveal some fairly complex behaviors, such as nonuniform slip motions along individual fractures and sub-vertical fractures that sometimes open and close simultaneously at different elevations. Slip motions along sub-vertical fractures near the heater plane were relatively large and well correlated with temperature. The heating phase deformations were only partially recovered during cool-down. The fracture deformation data show that fractures deformed in conjunction with water movements and associated temperature fluctuations during more » the test. Simultaneous slip and aperture data also provide estimates of fracture dilation angle. « less