To study the characteristics of sandstone crack propagation under hydraulic coupling

sandstone laboratory tests were conducted under different seepage pressures and confining pressures. Under the same effective confining pressure

it is shown that the rock brittleness index becomes higher as the seepage pressure increases

while the crack initiation stress

the crack damage stress

and the peak stress decrease gradually. The initial volumetric strain of the crack decreases

and the volumetric strain of crack propagation decreases firstly and then increases afterward. The growth rate of the crack axial strain and the crack circumferential strain are both increasing that corresponding to the damage stress and the peak stress

however

no obvious relation is observed between the growth rate of the crack volume strain and the seepage pressure. Under the same seepage pressure

the initiation stress

damage stress

and peak stress gradually increase as the effective confining pressure increases. In addition

the growth rates of the crack axial strain

circumferential strain and volumetric strain increase gradually during deformation that corresponds to the crack initiation stress

damage stress and peak stress

respectively. When comparing the different growth rates of crack strain for a tested sandstone specimen

it is found that the strain growth rates have the following order: the crack axial strain > the crack circumferential strain > the crack volume strain.