Micro-cracks are one of the degradation mechanisms in rocks and concrete structures. For serviceability design, it is important to understand the microcrack behavior in the host rock around tunnels during excavation. This study aimed to annex the specifics of the stress level (state) to the excavation damaged zone (EDZ) definition. Further, the influence of aggregate shape and water binder ratio on the crack behavior of cement-based materials was also investigated. To achieve the aim of this study, inclined shear tests (ISTs) were conducted on scaled non-hollow and hollow artificial rock samples. The samples were made of differently shaped aggregates (angular, A, and rounded, R) at varying water binder (w/b) ratios (w/b= 0.23 and w/b=0.35). Moreover, discrete element (DEM) simulations of the tests were carried out and their output was compared against the tests.

There was good agreement between the test and DEM simulations, thereby validating the capability of the variable bond property model proposed in this study to be used for crack evaluation studies in brittle materials. New definitions of the EDZ incorporating the stress state have been proposed. The crack mechanism under varying shear angles, water binder ratio, and differently shaped aggregates is also presented. The results indicate that the water binder ratio only affects macro-parameters i.e., Young’s modulus (E) and Poisson’s ratio (v). The cracking in samples made of angular (A) aggregate seems concentrated but sparse. The ability of A-aggregates to interlock limits the spread and intensity of cracks in samples made of angular aggregates, whether in hollow or non-hollow samples. The rounded (R) aggregates on the other hand have no interlock capability, as a result, the cracking is more widespread and intense. The acoustic emission (AE) events seem to align themselves along the direction of the resultant force or parallel to the shear planes and around the hollow openings. The DEM’s broken bonds, on the other hand, seem to propagate in the direction parallel to the loading plates bearing the applied external major principal stresses. At a low load level (LL), only microcracks occur in the sample, when LL increases to generally between (47-60) %, localization occurs (i.e., micro-cracks populate the shear zone), and the microfracture slowly transforms to macro-fracture. Finally, the presence of the internal balancing support, pi, seems to lessen the extent and severity of the cracks around the opening for anisotropic loading cases, as observed from both tests and DEM results.

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