Cracks Evolution and Mechanical Properties of Granite with Random Damage under Freeze-Thaw Action

Freeze-thaw cracking is considered to be one of the main reasons for the failure of low permeability hard rock in the high cold area, repeated freezing-thawing will lead to increased damage and intensity weakening of rock mass. Granite samples with random damage were obtained through temperature impact test, and cyclic freeze-thaw tests were carried out. CT and nuclear magnetic resonance tests were used to study the evolution process of microscopic cracks in granite during freeze-thaw cycle, and uniaxial compression tests were used to study the weakening law of its mechanical properties. The results show that: The damage of granite under the action of freeze-thaw cycle is mainly caused by the expansion and connectivity of the initial fissure, and the porosity and the proportion of macropores increase gradually with the freeze-thaw cycle. It is difficult to form long and large freeze-thaw fissures due to the mutual influence and restriction of the initial fissures distributed randomly, and the fissures are mainly distributed in irregular network. With the progress of freeze-thaw cycle, the permeability of rock increases gradually and the saturation wave velocity presents a unimodal curve form of first increasing and then decreasing. The degradation of rock strength follows the form of exponential function, and the degradation relationship between strength value and elastic modulus value of rocks with different initial damage degree is similar under the condition of long-term freeze-thaw weathering, and may eventually tend to the same level. The research results have important reference values for the long-term mechanical properties evaluation and engineering stability evaluation of crystal rocks in cold regions.