Abstract:

Permeability is one of the key factors in hydro-mechanical coupling study for underground engineering. A series of cyclic triaxial compression tests were conducted with red porous sandstones; the axial permeability was calculated according to Darcy’s law during the failure process. Based on the mechanical and permeability results, the influences of mean stress and stress cycles on permeability were investigated according to stress-strain curves and deformation modulus evolutions. Some conclusions are drawn: (1) With the increase of axial strain, permeability is consistently decreased in initial compaction and elastic deformation stages; during the plastic deformation stage, the reduction ratio of permeability is gradually decreased; in the end, permeability is even increased under low confining pressure. (2) The skeleton grain compaction causes porosity decrease, consequently permeability decreases; an empirical function is proposed to describe the relationship between permeability and mean stress. (3) During the stress cycles, the irreversible permeability behavior is induced by the irreversible deformation of skeleton grains. (4) There is a weak augment of permeability in post-peak stage, which shows the effect of induced cracks corresponds with the one of pore, the augment extent has a negative correlation with confining pressure, for porous sandstone.

Key words: permeability, sandstone, porosity, stress cycle, mean stress