In situ stress measurement by the stress relief technique using a multi-component borehole instrument

Abstract

Abstract We have developed a two-dimensional method for calculating principal stresses on a plane by measuring strain changes obtained by the stress relief technique using a multi-component borehole instrument. If the ratio of the radius of the core to that of the borehole is 1.4–2.0, a uniform strain change occurs in any stress field due to the overcoring. It is therefore desirable that the radius of the core obtained by overcoring is larger than that of the borehole by a few orders of magnitude. We applied the proposed calculation method to a stress measurement performed at the Hishikari mine, southwest Japan. The maximum and minimum principal stresses were determined to be 5.0 and −0.2 MPa, respectively. The nearly vertical stress was estimated to be 1.5 MPa, which was merely 30% of the predicted vertical stress (5.6 MPa). One of causes of the small vertical stress obtained in this study is considered to be the limitation of the two-dimensional method for calculating principal stresses.