Study on Mechanical Properties of Water-Immersed Mudstone Based on Nanoindentation Tests

To investigate the alterations in mechanical properties and damage mechanisms of water-immersed mudstone, the mudstone from the weak interlayer of an open-pit coal mine in eastern Inner Mongolia, China, was selected as the research focus. Mudstone samples with water contents of 0, 4.12%, 7.96%, 10.17%, and 12.73% were obtained through non-destructive immersion tests. Meso-mechanical tests on mudstone with different water contents were conducted using nanoindentation technology and scanning electron microscopy. The findings reveal a noticeable weakening of meso-mechanical properties of mudstone after water immersion. The elastic modulus, hardness, and fracture toughness all show a trend of non-linear attenuation with the increase of water content. Water-immersed mudstone exhibits changes characterized by volume expansion, decreased mineral cementation ability, reduced pore size, and increased quantity. The alteration in mudstone’s internal structure directly reflects the physical reasons for the weakening of mechanical properties after water immersion.