A comparative study between two rock stress measurement techniques at Luossavaara Mine

Summary

As part of a comprehensive geomechanical pre-investigation scheme, rock stress measurements were conducted at four locations, representing three different rock types, in the Luossavaara Mine, located within the Kiruna iron ore fields in northern Sweden. Two similar triaxial overcoring techniques, the CSIRO Hollow Inclusion Technique and the LUH Triaxial Technique, were used in a parallel fashion in order to obtain redundant results, but also with the intention of comparing the field applicability of the two methods.

The results show that the state of stress is characterized by a sub-horizontally directed maximum stress with a magnitude of about 10 MPa. The agreement in terms of stress results between the two methods was generally good.

The study demonstrated that the technical differences between the two devices used were of little significance as compared to the observed, often non-ideal mechanical characteristics of the rock. The latter added considerable uncertainty to the data, regardless of the measuring technique used, and it is therefore concluded that the rock quality is a major factor in the application of any overcoring method. Finally, it was shown that the biaxial test method, which is frequently used for the determination of rock properties in connection with stress measurements, is not always relevant for this purpose.