13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- the uncracked situations are also presented for purposes of comparison. In both instances, cracking of the halfspace region will lead to a reduction in the elastic stiffness of the rigid indenter. (a) (b) Figure 5. Influence of geomaterial cracking on the stiffness of the rigid indenter 5. Concluding Remarks The objective of the study is to examine the extent to which the load displacement of the rigid indenter is influenced by indentation fracture that can occur beneath the surface of the region that is being indented. In a geomechanics context, indention testing is carried out in order to determine the in situ properties of the geomaterial. Studies of this type serve two purposes; first it will alert the user to the stress levels that can lead to the development of cracking in the indented region. Modern acoustic emissions monitoring could be used to supplement the experiments. Secondly, if fractures occur it will influence the interpretation of the in situ deformability characteristics of the geomaterial region. The boundary cracking will generally lead to a lower estimate of the in situ modulus. The methodology described here is not without constraints, the most important of which is the assumption that some estimates can be made of the fracture toughness of the geomaterial as interpreted through the critical Mode I stress intensity factor. This pre-supposes that this parameter can be estimated from either laboratory tests or preferably in situ fracture tests conducted by flat jack expansion testing of surface slots cut into the rock surface. Acknowledgements The work described in this paper was supported in part by the James McGill Professorship, awarded by McGill University and in part by a Discovery Grant awarded by the Natural Sciences and Engineering Research Council of Canada.
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