Mechanical damage and aging characteristics of artificial pillar materials in moist environments: insights from humidity-controlled experiments and acoustic emission analysis

This study investigates the mechanical damage properties of artificial pillars in moist humid environments using specimens obtained from the mill mining area of Wengfu phosphate rocks. A custom-made humidity control device to provide four relative humidity levels (70%, 80%, 90%, and 100% RH). The mass and size of each specimen were tracked over time and unconfined expansion, uniaxial, and triaxial compression tests conducted and a digital image correlation method used. Scanning electron microscopy (SEM) and an acoustic emission (AE) device were used in this study to analyse the temporal changes in microstructure, expansion, mass loss, and corrosion depth, and assess the effects of humidity on macroscopic mechanical properties respectively. The findings indicate that hydro-rock interaction leads to the transformation of crystal morphology and the formation of microcracks in specimens, and higher relative humidity levels cause greater changes in mass, size, and expansion. The uniaxial compressive strength (UCS) decreases with storage time, particularly in specimens exposed to 100% RH for 60 days. Cohesion and internal friction angle also decrease over time, with cohesion being more sensitive to humidity. These results provide construction of a mechanical damage model, which can contribute to the prediction and assessment of pillar deterioration in high-humidity underground environments.