## 7 Conclusions and Summary  
The main conclusion for the results presented is that the type of stress path influences the failure envelope, whereby the classic laboratory experiments overestimate the rock strength in comparison to the real in situ stress paths. This conclusion is derived for a RVE model, using distinct element simulations. The latter were earlier calibrated at laboratory scale [54; 55]. The simulations clearly indicate the importance of (micro-)fracturing during the entire interval of stress changes. This (micro-)fracturing influences the macro-fracture and the strength. The simulations also indicate that the effect is significant. Strength reduction values of up to 40% were calculated. The strength reduction values in the simulations seemed to be realistic when compared to some published laboratory experiments [16; 20; 28]. In situ rock can undergo very complex stress paths. In this study, three basic stress paths were analysed. First, the conventional loading experiments, whereby the minor principal stress was kept constant, and the major principal stress was increased till failure. These simulations were close to the conventional compressive tests. The other two stress paths were close to the in situ change of stress around an excavation. The second stress path was rather the opposite of the first ones. For the second stress path, the major principal stress was kept constant, and the minor principal stress was decreased until failure occurred. The simulations that started from an initial isotropic stress state, followed by unloading one stress component, resulted in the weakest failure envelope. The simulations close to the conventional loading resulted in the strongest failure envelope and, thus, significantly overestimated the real in situ strength. The third basic type of stress path was the simultaneous increase in the major principal stress and decrease in the minor principal stress with the same absolute stress increments. The failure envelope of this third type was situated between the two previous envelopes. If the second type of stress paths was applied, but starting from an anisotropic stress state, the failure envelope for a large anisotropy moved closer to the one of the conventional loading paths. For these additional simulations, the initial minor principal stress was decreased. The variation of the fracture mode (i.e., tensile, shear, or mixed) during the stress changes showed some interesting observations. The start of all (micro-)fracturing in the simulations was characterised by tensile failure. This tensile (micro-)fracturing started at small load increases of the major principal stress for the stress paths close to the conventional loading experiments. At the end of the stress path, the predominant fracturing mode was shear. At the point of macro-failure, the sum of the proportion of shear and mixed modes varied between 64% (unconfined loading) and 82% (largest confinement stresses) of all activated contact elements. It was difficult to conclude if this was also what happens in the laboratory when studying acoustic emissions. For cored specimens, the Kaiser effect could play a role [34], and this could incorrectly result in an absence of acoustic emission for low stress levels in laboratory experiments. The black box models were not affected by the memory effect, as no coring, i.e., stress relaxation, took place. [PERSON] and [PERSON] [43] clearly observed acoustic emissions from the start of axial loading in a triaxial test set-up, i.e., similar to the simulations. The analysis of the recorded signals indicated that the predominant failure mechanism was in shear mode, also at the start of loading. However, non-negligeable amounts of tensile and mixed mode cracks were recorded from the initial cracks until full failure occurred. A similar observation was made for uniaxial [46] and biaxial compression tests [31].