Clay minerals separation in soft rock driven by the liquid bridge force during water–rock interaction

Mineral change and micropore development are important deterioration features of soft rock during water–rock interaction, but ignoring the differences and contributions of potential physical and chemical processes in existing laboratory studies. This paper carried out multiple micro-measurements on mudstone and sandstone after powder immersion and wetting–drying cycles of coarse grains, and proposed a liquid bridge model to distinguish the potential microscale process. The results indicate a complementary relation of mineral composition in the sieved fine particles, increasing clay minerals, and decreasing detrital minerals and cement with wetting–drying cycles. The variation in mineral and ion is slight after 320 days immersion. Micropores develop along mudstone boundaries after the wetting–drying cycle, and fewer clay minerals are found in sandstone whose skeleton of detrital minerals remain undamaged. The repeating liquid bridge force, varied in direction and magnitude, softens the cement strength inter minerals and induces them detaching from rock skeleton and remaining micropores. Combining with the weak chemical action, the rock damage evolution driven by the liquid bridge force helps us clarify the specific microscale processes involved in a short period of water–rock interaction, on the mechanism responsible for desiccation cracks, water-soil erosion and rock slaking.