Present status of mechanical investigation in deep rock mass. Initial stress measurements with various methods

Initial stress measurements have been performed at the Kamaishi and Tono mines using the hydraulic fracturing, overcoring deformation rate analysis, acoustic emission and differential strain curve analysis methods. The purpose of the measurements were to assess the applicability of each method in sedimentary (Tono) and crystalline rock (Kamaishi) environments and to determine the three-dimensional stress state in both mines. The results indicate that it is preferable to use more than one measurement method as each has certain limitations and may be affected by local lock mass conditions in different ways. The measurement layout needs to be considered carefully and the results analyzed with regard to the local site geometry, overlying topography and regional-scale tectonic stress regime. (author)