Experimental observation and numerical investigation on propagation and coalescence process of multiple flaws in rock-like materials subjected to hydraulic pressure and far-field stress

•A newly similar material (cement mortar) is used to simulate rock specimens.•Laboratory tests on specimens with multiple flaws under UCS and BCS are performed.•Two schemes in inclined flaws are considered: with water pressure and no water.•The crack propagation and coalescence laws have been obtained by laboratory tests.•The CDEM codes have a good ability to simulate the whole failure process. In this paper, a newly developed rock-like material (cement mortar) was proposed. Multiple flaws (including horizontal and inclined flaws) were prefabricated in the testing specimens, and a number of specimens subjected to hydraulic pressure and far-field stress were performed to study the crack propagation and coalescence process. Experimental results show as following. (1) Under uniaxial compressive condition, the propagation path and direction of preexisting flaws change obviously after the inclined flaws meet the horizontal flaws during the propagation process, and the phenomenon of ‘displacement jumping’ appears. (2) Under biaxial compressive condition, the increase of lateral pressure suppresses the initiation of cracks and secondary cracks at the ends of the inclined flaws. Under the condition of high lateral pressure, these inclined flaws would not propagate through the horizontal flaws and the failure mode changes from splitting to shear failure. The shielding effect of horizontal flaws on stress transfer is gradually increased. (3) Under the combined action of internal water pressure and far-field stress, with the increase of internal water pressure, the maximum principal stress distribution at the tip of wing crack in uniaxial compression gradually decreases, and the initiation stress, initiation angle and peak strength are also gradually reduced. The crack propagation and coalescence laws obtained by numerical simulation based on Continuum-based Discrete Element Method (CDEM) are basically in good agreement with the experimental results. The numerical analysis of the inclined flaws with different internal water pressures penetrating through the horizontal flaws without water pressure is also carried out. With the increase of internal water pressure, the inclined flaws firstly initiates the coplanar crack and then generates the wing crack. When the wing crack propagates though the horizontal flaw, the propagation path also changes. Under the combined action of internal water pressure and far-field stress, the lateral pressure also suppresses the initiatio