Experimental study on crack coalescence behavior of double unparallel fissure-contained sandstone specimens subjected to freeze-thaw cycles under uniaxial compression

To study the rock fracturing characteristics in cold-region engineering, uniaxial compression tests are conducted on double unparallel fissure-contained sandstone specimens subjected to freeze-thaw (FT) cycles. First, the effects of FT cycles on the water absorption, peak strength, initiation stress and deformation behavior of flawed sandstone specimens are investigated. The water absorption, uniaxial compressive strength, initiation stress, elastic modulus and deformation modulus of flawed sandstone specimens decrease with an increase in the number of FT cycles. However, the peak strain of flawed sandstone specimens increases with an increase in the number of FT cycles. Second, the cracking processes of flawed sandstone specimens are investigated in detail via images captured by a high-speed digital video camera system. The relationship between the real-time crack coalescence and the axial stress-strain curve of flawed specimens, which evaluates the macroscopic deformation characteristics of precracked rock subjected to FT cycles well, is considered. Third, the interaction mechanism of fissures in rock specimens is discussed. Fourth, the influence of water and temperature on the rock-weakening process is discussed. In this study, during the rock FT cycle weakening process, the effect of water, including the dissolution effect and the stress effect, is analyzed, whereas temperature damages the rock by means of different temperature gradients and the phase transition of water. Finally, the local strong fatigue-damaged zones around the fissure tips of sandstone specimens are also analyzed. These experimental results are helpful to improve the understanding of fracture mechanisms of a rock mass in cold-region engineering.