# Comparison of DFN Modelled Microfracture Systems with Petrophysical Data in Excavation Damaged Zone
## 5 Conclusions  
The physical and mechanical properties of drill core specimens were determined as a part of investigations into excavation damage in the dedicated study area. Additionally, microfractures in 16 specimens were analysed and used as a basis for DFN modelling. Composition was analysed via thin sections and microfracture network properties via tinted epoxy impregnated rock disks with a MATLAB algorithm. The possible influence of drilling, cutting, grinding, and polishing on the specimens was considered and concluded not to affect the results of individual specimens to any significant degree.  
There was a notable difference in resistivity between the pegmatoid and pheissic specimens, even though previous studies have shown that the resistivity distributions of Olkiliuoto pegmatoids and veined and diatexitic gneisses are similar [6; 32]. Furthermore, the observed differences in the resistivity of water-saturated specimens were found to be controlled mainly by differences in porosity [6]. As the observed porosities of the specimens did not differ significantly, the observed differences in the resistivities are likely due to differences in the rock matrix and the resulting differences in the type of microfractures, such as their orientation and following interconnectivity. This hypothesis was supported by the analysed thin sections and simulations: fractures in gneiss were short and mostly in one preferred orientation, likely controlled by foliation, whereas the fractures in granite were longer and had two preferred orientations. This suggests that gneiss and granite may suffer different types of excavation damage. A complementary or alternatively measure for the bulk porosity could be the microcrack porosity determined from mechanical testing [34]. In conclusion:  
* The number of large microfracture clusters and maximum number of fractures per cluster increases linearly with increasing volumetric granite content.
* The total number of connected fracture clusters is negligible from the point of view of hydraulic conductivity in both rock types.
* No systematic changes in the geometric parameters of the microfracture networks were observed with respect to depth, while differences between gneiss and granite were observed.
* This suggests that excavation does not cause detectable perturbance of the intact crystalline rock's microfracture porosity, i.e., that the excavation damaged zone cannot be identified based on changes in the parameters of the microfracture networks.
* The disturbed EDZ layer observed by geophysical methods may be caused by larger-scale fractures not present in the relatively intact specimens.  
Conceptualization, R.K., D.K. and L.J.; methodology, R.K., D.K., G.D. and L.J.; software, D.K. and G.D.; formal analysis, R.K. and D.K.; investigation, R.K., D.K. and L.J.; writing--original draft preparation, R.K. and D.K.; writing--review and editing, R.K., D.K., G.D. and L.J.; visualization, R.K. and D.K. All authors have read and agreed to the published version of the manuscript.  
This research is based on work funded by Posiva Oy. This research was funded by the Academy of Finland, grant number 319798.  
Not applicable.  
Restrictions apply to the availability of these data. Data was obtained from Posiva Oy and are available in the cited working reports at www.posiva.fi (accessed on 1 February 2021) or from the authors with permission of Posiva Oy.  
We would like to thank Posiva Oy for access to the data and the possibility to publish the results.  
This research is based on work contracted by Posiva Oy. The views expressed are those of the authors and do not necessarily reflect those of Posiva Oy.