To enhance national energy security

recent years have witnessed an increase in state investment directed towards the research and development of compressed air energy storage (CAES) technology. These initiatives are inherently more complex than traditional projects

as the stress relaxation characteristics of geological formations

particularly rocks

are influenced by a multitude of factors. According to the characteristics of CAES engineering

stress relaxation experiments of salt rock under barometric stress coupling were carried out from a new perspective to explore the stress relaxation characteristics of salt rock under different air pressures and axial starting stress conditions. The results show that: (1) The macroscopic behavior of stress relaxation in salt rock is independent of air pressure

and the process can be categorized into three distinct stages: rapid relaxation

decelerated relaxation

and stable relaxation. Notably

the rapid relaxation phase accounts for approximately 50% of the total relaxation

while the stable relaxation phase represents the predominant portion of the entire relaxation process. (2) The stress relaxation behavior of salt rock is significantly influenced by both axial starting stress and air pressure. Specifically

increased axial starting stress and air pressure correlate with heightened initial stress relaxation rates

greater relaxation rates

and an enhanced degree of stress relaxation during the stable relaxation phase. (3) Under cyclic pressure conditions

the stress relaxation of salt rock exhibits a cyclic relaxation pattern

with the relaxation curve being governed by the stress relaxation curve of salt rock at constant pressure

corresponding to its cyclic upper and lower limits. (4) Environmental scanning electron microscopy (ESEM) images of the relaxed salt rock reveal that the formation and propagation of micro-cracks constitute the primary mechanism of internal damage within the salt rock. Post-relaxation

the meso-structural damage observed in the salt rock includes grain debris

intragranular cracks

intergranular cracks

and trans-granular cracks. (5) The improved nonlinear two-element generalized Maxwell relaxation model can better describe the stress relaxation behavior of salt rock under different starting stresses and pressure conditions

and provide a certain reference for the stability assessment of salt cavern compressed air energy storage.