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After a brief review of the overcoring technique, two new borehole instruments for stress measurements in rock masses are described. These instruments enable the change in diameter and axial strain to be measured. The C.S.I.R.-triaxial cell in the version of the ISETH-Huggenberger is also discussed. Several types of error influencing the results of measurements have been observed. Some of them arise in connection with the measuring technique and arc closely related to the instrument which is used. Serious difficulties stem from nonlinear, anisotropic and non-elastic material behavior even in the case of hard rock. The extrapolation of local values of the state of stress to a representative large volume of rock is also faced with several difficulties such as the effect of discontinuities and inhomogeneities near to the measuring point. However, a great number of measurements with several types of instruments and a very careful laboratory study of the deformational behavior of the rock cores help to improve the quality of the final results for a specific area. In the opinion of the authors the reliable determination of in-situ stresses is still a very difficult task, which in many cases cannot be performed satisfactorily.
Authors:Grob, Hans and Kovári, Kalman and Amstad, Christian
Index Terms:measurements; Stress measurements; rock; TunnelingGroup; tunneling; underground openings; mechanics; Amstad, Christian; Grob, Hans; Kovari, Kalman
Further Information:Date published: 1974