Rock masses commonly contain discontinuities in the form of cracks and joints. Under various loads, new cracks initiate from the tips of pre-existing cracks (flaws). Propagation of new cracks ultimately leads to crack coalescence and flnal failure of the medium. In this paper, crack propagation and coalescence mechanism in rock-like materials (gypsum specimens) containing two parallel and open flaws under uniaxial compressive loads are experimentally investigated. In cubic specimens with two inclined flaws, the length of connection line between two flaws (bridge distance) and connection line inclination angle (bridge angle) are varied under fixed flaw angle and flaw length and the crack propagation and coalescence mechanism are studied. Two types of cracks initiate from the tips of the flaws: wing cracks and secondary cracks. Wing cracks, secondary cracks or combination of them produce the coalescence of the flaws. For bridge angle of 90◦, the bridge distance of two flaws has no effect on the crack propagation and coalescence pattern but the bridge angle has important role and controls the propagation and coalescence pattern. For different bridge angles (45◦ −120◦), four coalescence mode including shear, shear – tension, tension – shear and tension modes are observed.

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