Numerical and Experimental Study on the Cracking Behavior of Marble with En-Echelon Flaws

En-echelon fractures have been commonly observed in nature. To understand the interaction of en-echelon flaws, numerical simulation with flat-jointed model and laboratory experiment has been conducted on specimens containing en-echelon flaws of various configurations. With reliable micro-parameters of the flat-joint contact through a comprehensive calibration, numerical results reveal a strong interaction in flaw configurations of extensional bridges but a mild interaction in flaw configurations of contractional bridges. The patterns of linking cracks are found to be dependent on the flaw configurations. Furthermore, two typical linking cracks, tensile and shear cracks, are identified in terms of contact force evolution, crack development, micro-components and damage zone width. Experimental results not only verify the above conclusions given by simulation, but also provide more distinctions between tensile and shear cracks in grain scale. Based on these findings, an empirical correlation is suggested between debonding behavior in PFC models and microcracking behavior in laboratory experiments. Finally, the tendency of crack initiation stress and peak stress in simulation and experiment is compared and explained with respect to the flaw-array angle. A good agreement between simulation and experiment indicates the capability of the flat-jointed model of PFC2D in handling complex crack coalescence problems in rocks.