Variations of pore structure in Wanzhou sandstone subjected to different wet-dry cycles and treated with Na2SO4 solution.

Analysis of changes in rock pore structure under the action of dry–wet cycles is of great significance to the evaluation of slope stability in the reservoir area. We have selected the purple sandstone as the experimental sample in the Three Gorges Reservoir area of Wanzhou District, Chongqing City of China, and conducted dry and wet cycle tests under different Na₂SO₄ solution concentrations (0%, 1%, 3%, 5%). Colorimetry, ultra-eye observation (using the Hi-View software), and nuclear magnetic resonance (NMR) techniques were used to study the change in the sandstone pore structures and its surface characteristics. The results reveal that (1) with the increase in the Na₂SO₄ concentration and number of cycles, the total chromaticity (E*) increases. Simultaneously, L*, which represents light and shade (black and white) decreases, the value of a* (representing red and green), and the value of b* (representing yellow and blue) increases. (2) The greater the concentration and the higher the number of cycles, the smaller the number of micropores (< 0.1 μm) in sandstone. The larger the proportion of macropores (> 0.1 μm), the better the connectivity of the internal structure, and the greater the porosity. This study has a certain reference value for the slope stability evaluation of the Three Gorges Reservoir Area in Wanzhou District, Chongqing City of China. [ABSTRACT FROM AUTHOR]