Experimental research on aperture evolution of single granite fracture under stress-chemical solution permeation condition

摘要

Experiments of granite with single fracture under constant triaxial stress and chemical solution seepage are carried out to study the evolution of fracture aperture (and related permeability) under stress-chemical solution permeation. Experimental results show that with both acid and alkaline solution seepage the fracture aperture decreases monotonically. The rapid initial closure happened during the first 300 hours of the tests, followed by slowing closure till a stable final aperture, which is obviously greater under acid flow than that under alkaline flow. The ion concentration of solution from the outlet was recorded during the test, and the 3D laser scan and mineral morphology of fracture surface before and after test were also measured. Under acid solution flow, the SiO2 and Al3+ concentrations of outlet solution increase with time, indicating that the minerals (mainly feldspar and mica) at contact surface and the free surface are dissolved constantly. Under alkaline solution seepage, the SiO2 and Al3+ concentrations of outlet solution are significantly lower than those under acidic flow, indicating that the pressure dissolution at contact points leads to the closure of fracture so that the reaction ceases gradually with the increase of contact area. The results confirm that the different evolutions of fracture aperture are due to the competition between the contact surface solution and free surface dissolving.