## 5 Comparison between the RVE Model and Published Laboratory Experiments

Table 5: Percentage of activation modes (i.e., tensile only, mixed mode, or shear only) for the unloading of the minor principal stress, followed by the loading of the major principal stress, whereby three stress levels were considered for the change from unloading to loading, i.e., 10 MPa, 12.5 MPa, and 15 MPa. (a) Percentage at change from unloading to loading for contact elements activated at that moment; (b) percentage at failure for activated contact elements. Figure 10: Stress paths for uniaxial unloading followed by uniaxial loading between initial isotropic stress state of 25 MPa and failed stress level, superimposed on failure envelopes for the three basic types of stress paths (Figure 5). Switches between loading and unloading phases were at minor principal stresses of 10 MPa (left line), 12.5 MPa (middle line), and 15 MPa (right line). (a) Full stress paths presented; (b) zoomed detail (different vertical and horizontal scale). Figure 11 presents the variation of the mode of contact element activations for the three simulations, i.e., the unloading of the minor principal stress, followed by the loading of the major principal stress. The total stress path interval is considered in these graphs, i.e., the sum in absolute terms of the unloading interval of the minor principal stress and of the loading interval of the major principal stress until failure. In other words, two different stress directions were added, which is unconventional, but it was justifiable for these specific graphs. The change from unloading to loading or the change from horizontal to vertical stress paths is indicated by the coloured vertical lines. By referring to the basic uniaxial unloading simulations, i.e., S1(=),S3(unl), it was observed that the contact elements only failed in tension during the first part of the unloading interval (Figure 7b). Thus, for the simulations of the unloading, followed by loading in the other direction, it was logical that tensile activation was the predominant mode during the first phase, i.e., the unloading interval. When unloading until 12.5 MPa and 15 MPa, only tensile activation was observed (Figure 11b,c, Table 5 (a)). When the unloading covered 15 MPa (Figure 11a, light blue colour), i.e., until a stress of 10 MPa, a limited number of contacts also failed in shear at the end of this phase, but the large proportion of failed contacts was in the tensile-only mode, i.e., 86% of all failed contacts at that moment (Table 5 (a)). For this unloading interval, i.e., over 15 MPa, the weakening of the rock material was the largest in comparison to the two other unloading intervals. At the end of this interval, about 23% of all available contact elements had failed, i.e., for a final unloaded stress of 10 MPa (Figure 11a). For the shorter unloading intervals, these percentages were about 14.5% and 9.5%, i.e., until 12.5 MPa and 15 MPa, respectively. Figure 11: Variation of the contact failure modes (i.e., tensile only, shear only, and mixed mode) for stress paths of uniaxial unloading followed by uniaxial loading (see Figure 10), as a function of the entire load interval (i.e., sum in absolute terms of unloading and loading intervals). Switches between loading and unloading phase were at minor principal stresses of (**a**) 10 MPa; (**b**) 12.5 MPa; and (**c**) 15 MPa. In the successive loading phase, the amount of tensile activation remained large for the confining stress of 10 MPa. For this case (Figure 11a) and at the moment of full failure, 55% of all failed contacts were in tension-only mode, 26% were in shear-only mode, and the remaining 19% were in mixed mode (Table 5 (b)). For the basic uniaxial loading simulations for a confining stress of 10 MPa (Figure 7a, Table 2 (a)), i.e., S1(loa),S3(=), these percentages were 22% tension, 56% shear, and 22% mixed, respectively. The difference for both stress paths was significant.