Quantification and acoustic emission characteristics of sandstone damage evolution under dry–wet cycles

Rocks are continuously affected by dry–wet cycles, which leads to intensified weathering and deterioration of the mechanical properties and often triggers engineering disasters. This study analysed the changes in the mechanical properties and microstructure of sandstone under dry–wet cycles. Based on the box dimension theory and the associated dimensions, the fractal dimension and correlation dimension were developed through digital images and time-series parameters to analyse the microstructural features and acoustic emission (AE) in MATLAB. The degree of microstructure damage under different dry–wet cycles was determined, and the relationship between the microstructure characteristics, fracture development trend, fractal dimension, and correlation dimension was established. The uniaxial compressive strength, elastic modulus, p-wave velocity, and resistivity of the sandstone decayed in distinct stages as the number of dry–wet cycles increased. The degree of microstructure damage was observed to be directly proportional to the fractal dimension. The physical and mechanical properties of the sandstone exhibited a significant relationship with the fractal dimension; it could be used to quantitatively describe the parametric characteristics of the sandstone. The change law of AE energy is consistent with the damage process of sandstone. Based on the analysis of the correlation dimension and sandstone microscale failure, its variation characteristics could be used to quantitatively evaluate the trend of sandstone fracture development and microstructural characteristics. The research results provide a reference for further exploration of the deterioration mechanism and engineering application of the sandstone during dry–wet cycles.