Investigation into geochemical mechanism and microscopic degradation pattern of red clay induced by acid rain infiltration

Elucidating the geochemical degradation mechanisms of red clay under acid rain infiltration is essential for evaluating long-term slope stability and guiding targeted disaster prevention in acid-rain-prone regions. Combining multi-scale characterization (ICP-AES, XRD, SEM, PCAS) and PHREEQC geochemical modeling, this study systematically quantified the coupled effects of degree of compaction (DOC) and pH on mineral evolution, pore structure, and aggregate stability of red clay. Results confirmed selective mineral dissolution, with cation release following the order Ca2+>Fe3+>K+>Mg2+>Al3+ and peaking at 86% DOC and pH 2. PHREEQC simulations agreed well with experimental data, identifying three hierarchical degradation patterns (10−6–10−4 mol): carbonate/free oxide dissolution, illite-to-kaolinite transformation, and diffuse double layer reconfiguration. Acidification transformed soil from dense aggregation to loose porosity, with a maximum 33.8% pore size increase and 54.5% aggregate stability loss, while higher DOC significantly suppressed degradation. These findings establish a quantitative geochemical-microstructural coupling framework for red clay slope protection.