Study on dynamic characteristics of sandstone-damaged by loading and unloading

To investigate the impact of unloading on the dynamic mechanical properties of surrounding rock in roadway excavation, sandstone specimens were subjected to loading and unloading at six levels ranging from 0% to 80% of the uniaxial compressive strength (UCS). Subsequently, an improved SHPB was employed to perform dynamic compression tests, aiming to analyze the mechanical characteristics of the sandstone at various degrees of loading and unloading damage, investigate fractal attributes, and examine the dynamic failure process. The study uncovered that the stress-strain curve exhibits three distinct stages. Correspondingly, a more suitable set of dynamic elastic modulus denoted as Ed1, Ed2, and Ed3, were defined. Using 45% of the UCS as the threshold for unloading stress (75 MPa), both the dynamic elastic modulus and dynamic strength displayed an initial upward trend, succeeded by a subsequent decline. In contrast, the defined damage peak strain ratio Isp and damage ultimate strain ratio Ism demonstrated the opposite trend, amounting to 45.64% and 51.03% at the threshold. In addition, increasing unloading damage stress (UDS) decreases the sandstone strain rate(smax and save) gradually. Simultaneously, the fractal dimension of the cracks exhibited a linear increase, ranging from 1.159 to 1.481. Similarly, the rock exhibited the lowest proportion of reflected energy and absorbed energy at the threshold. This holds noteworthy implications for examining the dynamic load response behavior of surrounding rock in roadway unloading, ensuring the dependability of blasting unloading techniques.