Infrared radiation test on the influence of water content on sandstone damage evolution

Abstract

The rock mechanics uniaxial compression testing system and a thermal imaging camera were used to research the influence of water on sandstone damage evolution and the concurrent infrared radiation (IR) characteristics on sandstone samples with different water contents. The field of view of the thermal imaging camera divided the sandstone surface into several small areas of equal area. When one of the small areas of sandstone ruptured (that was when a damage point was generated in the sandstone) the IR information from that area underwent abrupt changes. Based on this monitoring, a quantitative index of infrared radiation, the IR count (IRC), was adopted and investigated as the indicator for damage evolution of rocks that also linked damage intensity with the corresponding IR temperature. The research results showed that when the sandstone stress experienced a stress drop, the IRC will simultaneously undergo a sudden increase indicating that the IRC was controlled by the stress. However, this stress control on IRC decreased with increasing water content due to the softening effect of water on the sandstone. Among them, the control effect of stress on IRC reaches 100% for dry sandstone, which is reduced to 75% for sandstone with a water content of 0.5% and 66.7% for sandstone with a water content of 1.5%. The control effect of stress of saturated sandstone on IRC is 57.1%. For sandstones with other water contents, but at the same damage evolution stage, the average IRC (IRC¯) for sandstones showed an upward trend as the water content increased. Compared with other damage evolution stages, the IRC¯ of the water-bearing sandstone had the most significant difference in the failure stage, indicating that water had the most significant influence on the damage evolution of the sandstone in the failure stage. This IRC was generated at the location of a new damage point on the sandstone surface. Therefore, based on the instant of time node when the sandstone IRC suddenly increased, the IRC spatial distribution map at that corresponding time was drawn to accurately locate the sandstone damage and fracture area. The characteristics of the damage evolution process of sandstones with different water contents were the same over the time before the sudden increase in IRC, the damage points formed were disorderly distributed, and the number of damage points was less. The difference was that as the water content increased, the number of sandstone damage points became larger and more concentrated.