Energy evolution model and energy response characteristics of freeze-thaw damaged sandstone under uniaxial compression

Rocks will suffer different degree of damage under FT (freeze-thaw) cycles, which seriously threatens the long-term stability of rock engineering in cold regions. In order to study the mechanism of rock FT damage, energy calculation method and energy self-inhibition model are introduced to explore their energy characteristics in this paper. The applicability of the energy self-inhibition model was verified by combining the data of FT cycles and uniaxial compression tests of intact and pre-cracked sandstone samples, as well as published reference data. In addition, the energy evolution characteristics of FT damaged rocks were discussed accordingly. The results indicate that the energy self-inhibition model perfectly characterizes the energy accumulation characteristics of FT damaged rocks under uniaxial compression before the peak strength and the energy dissipation characteristics before microcrack unstable growth stage. Taking the FT damaged cyan sandstone sample as an example, it has gone through two stages dominated by energy dissipation mechanism and energy accumulation mechanism, and the energy rate curve of the pre-cracked sample shows a fall-rise phenomenon when approaching failure. Based on published reference data, it was found that the peak total input energy and energy storage limit conform to an exponential FT decay model, with corresponding decay constants ranging from 0.0021 to 0.1370 and 0.0018 to 0.1945, respectively. Finally, a linear energy storage equation for FT damaged rocks was proposed, and its high reliability and applicability were verified by combining published reference data,the energy storage coefficient of different types of rocks ranged from 0.823 to 0.992, showing a negative exponential relationship with the initial UCS (uniaxial compressive strength). In summary, the mechanism by which FT weakens the mechanical properties of rocks has been revealed from an energy perspective in this paper, which can provide reference for related issues in cold regions.