The Influence of Infilling Conditions on Flaw Surface Relative Displacement Induced Cracking Behavior in Hard Rock

Abstract

The relative tangential displacement (or slip) and relative normal displacement of flaw surfaces are two of the main factors driving crack initiation and propagation of rocks. In this study, uniaxial compression experiments are performed in flawed marble under different cases, i.e., open flaw and flaw filled by gypsum, cement and resin, and different flaw inclinations, to study the influence of infilling conditions on the flaw surface relative displacement (i.e., relative tangential and normal displacement) and the induced cracking behaviors, such as crack initiation, propagation and crack patterns. The digital image correlation (DIC) technique is used to trace the evolution of relative deformation across the flaw surface and cracking process of flawed specimens. The results reveal that the difference in flaw surface relative displacement, at a given load, is introduced by different infilling materials. Among the four types of flaws, the filled flaw with smaller relative displacement is less likely to initiate cracks than the unfilled flaw with larger relative displacement. Moreover, the crack initiation position, angle, and types are also dependent on the relative deformation between the flaw surfaces. With the increase of the stiffness of the filler or flaw inclination angle, the effect of relative normal displacement on the cracking behavior is weakened, while the effect of relative tangential displacement increasingly dominates. As a result, the filled flaw with smaller relative normal displacement makes wing crack initiation points closer to flaw tips. Moreover, the filler with higher stiffness makes the wing crack initiation angle smaller, improves the possibility of the quasi-coplanar crack initiation, and suppresses the initiation of anti-wing cracks from the flaw tips in hard rock.