ABSTRACT
The understanding of the in-situ stress state is a central concern in rock mechanics, both with respect to understanding geological processes of importance to underground operations, as well as for the design of engineered structures constructed in and on rock masses. Fairhurst (2003) gives an overview of the development of stress measurement techniques. He found that one of the earliest methods for stress estimation was the flat jack and the door stopper. Both methods were published in the 1950s. The former is sometimes classed in a group of techniques termed Surface relief methods; the latter is classed among Borehole relief methods. The analytical expression for the stresses and displacements produced around a circular hole in a continuous, homogeneous, elastic, isotropic medium developed by Kirsh 1898 has been applied in the evaluation of borehole relief methods. This was further enhanced when Leeman and Haynes (1966) proposed a solution for stresses in a thin walled cylinder, providing the theoretical background for 3-D overcoring cells. A third approach for stress estimations is the Hydraulic methods. Hydraulic fracturing (HF) was originally developed in the 1950s to stimulate production in petroleum reservoirs, and later proposed by Kehle 1964 to be used for stress determination. Later, the idea of hydraulic testing of pre-existing fractures (HTPF) was developed by
ABSTRACT: This paper reviews the latest developments for in-situ rock stress measuring techniques. The review is based on experience gained during the on-going site investigation programme for siting of a final repository for spent fuel in Sweden, and consequently focused on techniques used in slim holes in crystalline rock. Large scale measurements, such as back analysis from convergence measurements during tunneling, are also discussed. It is concluded that no major breakthrough in terms of new basic tools for stress measuring techniques have been recognized by the author during recent years. Yet, the continuous improvements in computerized control systems, logger technologies and increased computing capacity have provided an increased capability to estimate the state of stress – with higher standards in terms of data acquisition, as well as data processing and interpretation. In addition, research within rock mechanics has also highlighted physical processes that may be of importance to understand the state of stress via the measurement techniques. Thus, this paper reviews the development of measuring techniques, data acquisition and interpretations that are of significance in the stress estimation process. It also highlights the importance of employing QA routines when obtaining primary data, as well as during data evaluation.
