ABSTRACT
Intact rock strength, usually characterized by Unconfined Compressive Strength (UCS), represents a key parameter for performance and tool wear assessment for any hardrock excavation methods, i.e. TBM, drill & blast, roadheader or other mechanical excavation. An accurate assessment of UCS and its variation is therefore of crucial importance in the course of any preliminary site investigation in order to allow for appropriate tender baselines and reasonable bid estimates. Although “intact rock” is usually understood as a small volume of rock material, that behaves as a continuum and shows no significant influence of discontinuities, many rock types, including a majority of sedimentary and metamorphic rocks, might still incorporate internal structural features like lamination, bedding or foliation, which might not be discontinuities by definition, but might cause directional dependent behaviour. If insufficiently considered during sampling, testing and interpretation, such features inherit the risk of artificially biassed strength results and unnecessarily broad value ranges which might even question the overall significance of UCS as input parameter. This paper includesexperimental test results on directional strength behaviour, presents approaches for the classification of anisotropy, displays examples for the practical impact of anisotropy on strength and states recommendations for sampling and testing of such rock types.
