Abstract: Slaking of mudstone in acid rain area is significantly stronger than that in non-acid rain area, and the slaking mechanism needs to be studied. Based on the formation and development characteristics of hydro-chemical coupled damage under acid rain, this paper took a landslide at Panzhihua city airport as an example, which is in a typical acid rain area. Silty mudstone rock samples located in the sliding zone were selected and processed. After that, a series of slaking experiments was comparatively carried out under different pH conditions. In order to explore the micro-mechanism of acid rain-aggravated slaking behavior of silty mudstone, we adopted a series of analytical methods, including analyzing cation composition changes in different pH slaking fluids, observing micro-structure change of samples before and after acid rain treatment as well as analyzing slaking failure modes of silty mudstone. Finally, an index named specific surface area increment index was introduced to reflect the impacts of acid rain-induced chemical damage on slaking behavior of silty mudstone. The results highlight that: the acid rain-induced chemical damage in silty mudstone was mainly caused by the dissolution of specific minerals, which provided extra paths for the slaking of silty mudstone. With the decrease of pH value of slaking fluid, the acid rain-induced chemical damage of silty mudstone increased, the slaking paths increased, the slaking failure mode changed, and the slaking residues were broken into finer fragments. The specific surface area increment index could well capture the fragmentation degree of slaking residuals. The more breaking the slaking residuals, the higher the specific surface area increment index, and the greater the slaking degree of silty mudstone. Conclusions of this paper provide theoretical reference for the evaluation of geotechnical engineering properties and reinforcement design in acid rain areas.

Key words: acid rain, slaking, acid rain-chemical damage, specific surface area increment, silty mudstone