Experimental Study on Mechanical Properties of Wind-Oxidized Sandstone Reinforced by Grouting Under Cyclic Loading and Unloading

To investigate the failure mechanisms of roadway-surrounding rock in the wind oxidation zone, where the rock experiences instability under cyclic excavation-induced loading and unloading, this study conducted experiments leveraging acoustic emission analysis, scanning electron microscopy, and a digital image correlation (DIC) system. The research focused on grouting reinforcement under varying gradation indices, examining its mechanical properties, deformation characteristics, and microscopic structure post-failure. Results show that as the gradation index increases, the peak strength of the grouted solid exhibits a non-linear trend, initially decreasing to a minimum of 9.40 MPa (a 40.4% drop) before rising again to a maximum of 15.76 MPa. The hysteresis loop observed follows a pattern of 'sparse-dense-sparse'. Additionally, the acoustic emission cumulative ringing count demonstrates a three-stage pattern of 'rising-active-quiet', with a similar initial decrease followed by an increase correlated with the gradation index. Using digital image correlation (DIC) technology, the study revealed the crack development characteristics of the grouting reinforcement. Higher gradation indices lead to wider localization zones, more extensive crack propagation, and greater damage. Microstructural analysis showed that PVA enhances the formation of hydration products, fostering stronger adhesion between these products and the cement matrix. This leads to a denser and more uniform microstructure, thereby enhancing the macroscopic strength of the samples. It provides a basis for practical mining engineering applications of grouting reinforcement of roadways in wind oxidation zones.