Damage Evolution and Acoustic Emission Characteristics of Sandstone under Freeze-Thaw Cycles

The deformation and fracture characteristics of rocks under freeze-thaw cycles were investigated by using uniaxial compression tests with acoustic emission (AE) monitoring. The results showed that the sandstone peak stress and elastic modulus decreased with an increasing number of freeze-thaw cycles, and the strain increased significantly. The rates of increase in the total energy and elastic energy decreased with an increasing number of freeze-thaw cycles. The freeze-thaw damage factor D_e was directly proportional to the number of freeze-thaw cycles. The total damage factor D was inversely proportional to the freeze-thaw cycles when the freeze-thaw-induced damage and load-induced damage were coupled. By analyzing the AE energy rate, event rate, amplitude, and frequency of the sandstone during damage, it was found that the amplitude varies irregularly with the freeze-thaw cycles and that the AE energy and event rates can better show the development of internal cracks in the sandstone. The peak frequency was the most sensitive and could be used as an index to predict when the sandstone ultimately failed. The increase in the number of freeze-thaw cycles encouraged the development of internal cracks in the sandstone. The crack characteristics change from mixed tensile-shear fractures before they undergo freeze-thaw cycles to tensile fracturing after a high number of freeze-thaw cycles. These research results provide a valuable reference for understanding the mechanisms of rock damage caused by freeze-thaw cycles as well as for making predictions about the safety of engineering structures in cold climates.