Stress measurements in high-stress zones using the modified doorstopper technique

Abstract

Of the existing in situ stress-measurement techniques, the doorstopper is particularly suited for use in highly stressed zones where core discing may occur. The main reason is that the doorstopper requires a very short intact core length to obtain a valid measurement in comparison with other techniques that use overcoring to perform stress relief, such as borehole-deformation gauges, CSIR (Council for Scientific and Industrial Research), and CSIRO (Commonwealth Scientific and Industrial Research Organization) gauges. The paper presents stress-measurement results obtained with the modified doorstopper technique in highly stressed granite, at the Underground Research Laboratory (URL) of Atomic Energy of Canada Limited. A brief description of the modified doorstopper technique and of a stress-calculation model that includes the nonlinear anisotropic behaviour found in highly stressed rocks is made. Stress-measurement results obtained at the URL with different techniques are compared with those obtained with the modified doorstopper cell. Key words : doorstopper, high stresses, anisotropy, nonlinear elasticity, core discing.