Experimental investigation on crack coalescence and strength loss of rock-like materials containing two parallel water-filled flaws under freeze-thaw

The freezing of water-bearing flaws has a much more serious threat on the stability of fractured rock slopes, because saturated flaws provide more liquid water for frost expansion and thus induces frost cracking. The freeze-thaw collapse of alpine mountains is mainly caused by the frost cracking of rock bridges between flaws. In this research, the frost propagation and coalescence process of two parallel water-filled flaws was investigated by experiment, by considering the effects of flaw angle and bridge angle. It indicates that the maximum frost heaving pressure in these elliptical flaws is more than 4 MPa, which is large enough to drive flaws propagation and cause bridge cracking. A considerable uniaxial compressive strength (UCS) loss occurs after freeze-thaw cycles when the flaw or bridge angle is close to the inherent rupture angle of intact samples, because the loading rupture coincides with new frost heaving cracks. Therefore, more attentions should be paid on these flawed rocks with flaw or bridge angles equal to the rupture angle, which is easier to rupture and fall down from the mountains. In addition, the unidirectional freezing mode is more conducive to drive the flaw propagation than the uniform freezing mode, because the frost heaving pressure under unidirectional freezing is much larger due to the ice plug effect, which means that the solid ice is like a plug blocking the mouth of cracks and preventing the water flowing outside. This study can provide a better understanding of the frost propagation of water filled flaws in rock masses and the stability of rock engineering under freeze-thaw in cold regions.