Hydraulic-fracturing measurmements in two boreholes near the Spent Fuel Test-Climax, Climax Stock, Nevada Test Site

Hydraulic-fracturing measurements are used to infer the magnitude of the least principal stress in the vicinity of the Spent Fuel Test-Climax, located in the Climax stock at the Nevada Test Site. The measurements, made at various depths in two exploratory boreholes, suggest that the local stress field is not uniform. Estimates of the least principal stress magnitude vary over distances of a few tens of meters, with the smaller values averaging 2.9 MPa and the larger values averaging 5.5 MPa. The smaller values are in agreement with the minimum-stress magnitude of 2.8 MPa determined in a nearby drift in 1979, using an overcoring technique. Jointing in the granitic rock mass and (or) the influence of nearby faults may account for the apparent variation in minimum-stress magnitude indicated by the hydrofracture data.