Splitting characteristics of diaspore-type bauxite in coal measure strata under water-rock interaction

The bauxite deposits in Shanxi Province are located within the Carboniferous-Ordovician composite aquifer system. Understanding the mechanisms of ore body weakening and fracture propagation due to water-rock interactions is essential for ensuring the safe and efficient mining of bauxite. This study focuses on the Loufan bauxite in Shanxi, conducting Brazilian tests on specimens with varying water saturations (0%, 25%, 50%, 75%, and 100%) to investigate tensile strength, damage evolution, and fracture energy characteristics. A parametric program was developed to quantitatively characterize the fracture surface morphology and study the effect of water saturation on the splitting characteristics. Molecular dynamics simulations and CT scanning tests were employed to elucidate the micro-mechanisms of water-rock interactions that weaken bauxite strength. Additionally, ESEM images were analyzed to reveal the fracture mechanisms at different water saturations. The results indicate that: (1) Diaspore, the primary component of the studied bauxite, exhibits strong hydrophilicity. (2) As water saturation increases from dry to fully saturated, the tensile strength decreases from 14.851 MPa to 6.364 MPa, and the fracture energy drops from 10 426.63 J/m² to 6 772.35 J/m², indicating a progressive weakening of its resistance to failure. (3) The Joint Roughness Coefficient (JRC) increases from 7.30 to 17.02, and the fractal dimension rises from 1.923 00 to 1.948 45, suggesting that the fracture surface morphology becomes increasingly complex. (4) CT scan results indicate that mineral expansion and dissolution are not the primary mechanisms contributing to strength weakening. (5) Molecular dynamics simulations and ESEM analysis reveal that water molecules interact with the diaspore crystal through hydrogen bonding, which reduces inter-crystal friction and alters the fracture mechanism. The failure transitions from transgranular fracture (dominated by the cleavage of Al-O covalent bonds) to intergranular fracture (dominated by the rupture of hydrogen bonds (O2-H…O₁)). Macroscopically, this results in rougher fracture surfaces and a gradual reduction in tensile strength. These findings provide experimental evidence for the mining of diaspore-type bauxite.