Effects of dry fractures on matrix diffusion in unsaturated fractured rocks

Abstract

Matrix diffusion has been recognized as an important mechanism affecting solute transport through unsaturated fractured rock, where a significant portion of the fracture network remains relatively dry and inactive in conducting liquid flow. This simulation study shows that dry fractures act as strong diffusion barriers to solute transport when such fractures divide the matrix into discrete blocks. Where fracture surface roughness causes certain amount of direct contact between matrix blocks separated by a dry fracture, the contacts of the matrix blocks provide conduits for liquid flow and molecular diffusion across dry fractures. Simulation results indicate that the presence of dry fractures and their discontinuities can considerably affect solute transport in unsaturated fractured rock, depending on the magnitude of molecular diffusion.