Experimental study on seepage–corrosion coupling characteristics of a single fracture in limestone subjected to acid mine drainage

Abstract

To investigate the influences of the acid mine drainage (AMD) in a closed coal mine on the corrosion and seepage stability of limestone with rough fractures, both distilled water and AMD solution were employed to implement seepage-corrosion tests on the seven sets of a single fracture of limestone specimens under different hydraulic conditions. We investigated the effects of confining stress and solution on the seepage parameters. Also, the mechanism of seepage reduction of fractured limestone caused by AMD solution was proposed. Moreover, COMSOL numerical software was used to simulate the chemical-seepage coupling field characteristics of a rough fracture under condition 4. The results are as follows: (1) The permeability, the Ca²⁺ concentration gradually decreases, and the osmotic stress, the total iron concentration gradually increases during the seepage process. (2) Differences between the bedding and matrix corrosion exist, the roughness of the fracture surface decreases, and “passivation” occurs on the surface, which makes the permeability decrease rapidly in the early stages and stabilize later. (3) The real-time permeability of fractured limestone under high confining stress is smaller than that under low confining stress and the sensitivity of permeability decreased with the increase of confining stress. (4) The numerical simulated results show the diffusion area of the solution on the fracture wall expands with increasing seepage-corrosion time and osmotic stress of the entrance section. This work will be of great significance to guide the treatment of AMD and the stability analysis of engineering rock masses.