Effects of wetting/drying cycles on pore characteristics in sandstone from Wanzhou, China

The microstructure and appearance of sandstone samples from the bank slope of the Three Gorges Reservoir of the Yangtze River in Wanzhou District, Chongqing, China were evaluated before and after wetting/drying cycles in aqueous solution using nuclear magnetic resonance spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Water/rock interactions including dissolution, ion exchange, hydration, dissolution and oxidation/reduction changed the mineral composition and microstructure of the rock mass media along with the pore structure and mineral particle shape of the rock mass. During wetting/drying cycles, the internal morphology of the sandstone gradually changed from neat and dense to fractured and loose. In greenish-grey sandstone, multiple wetting/drying cycles led to decreases in the proportions of micropores (0–0·01 μm) and small pores (0·01–0·1 μm), while the proportions of mesopores (0·1–1 μm) and macropores (>1 μm) gradually increased. In grey-white sandstone, multiple wetting/drying cycles also led to a decrease in the proportion of micropores, while the proportions of small pores, mesopores and macropores gradually increased. These results could provide a significant guidance for the further study of the stability of the slope rock on the reservoir bank and the formation of effective stability maintenance and reinforcement measures.