Influence of Coupling Action of Loading and Freeze-thaw Cycles on the Energy Conversion and Damage Characteristics of Sandstone Containing Multiple Flaws

In order to investigate the fracture mechanism of loaded jointed rock in the cold region,the freeze-thaw cycles and uniaxial compression tests were conducted on the sandstone specimens containing multiple flaws.The energy characteristic parameters were introduced to quantify energy conversion of the specimens containing multiple flaws and intact specimens under the different number of freeze-thaw cycles.Based on the statistic damage theory and strain equivalent principle,the damage model of loaded jointed rock under freeze-thaw cycle was established to study the correlation between the damage and energy conversion.The failure modes of specimens containing multiple flaws before and after freeze-thaw cycles are tensile and shear mixed failure.An exponential decay relationship is found between the mechanical properties and the number of freeze-thaw cycles.The energy storage limit and post-peak conversion rate of strain energy for specimens containing multiple flaws and intact specimens decrease with the increase of the number of freeze-thaw cycles.For the same number of freeze-thaw cycles,the energy characteristic parameters are larger for specimens containing multiple flaws than those of intact specimens.These indicate that the energy is released more slowly due to the effects of freeze-thaw cycles and the existence of multiple flaws.The relationship between the damage value at peak stress and the number of freeze-thaw cycles obeys an exponential growth function.The damage values of specimens containing multiple flaws are greater than those of the intact specimens.This is because the damage of freeze-thaw cycling is aggravated by multiple flaws.Data fitting further verified a high negative correlation between the damage value at peak stress and the post-peak conversion rate of strain energy.The higher the degree of rock freeze-thaw damage,the smaller the post-peak energy conversion rate.