Stress concentration factors for the flat borehole end for use in rock stress measurements

Uniaxial loading tests on blocks and cylinders of different materials, as well as a photoelastic model study, are described. From these tests the stress concentration factors around the flat end of a borehole, drilled into each block or model, are determined. It is shown that one of the stress concentration factors is related to Poisson's ratio of the material in which the borehole is drilled.