College of Construction Engineering��Jilin University��Changchun 130012��China

Through seepage tests under different loading and unloading confining pressures and different hydrau- lic gradients��the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture�� The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure�� With the increasing in the confining pressure��the permeability of the fracture decreases��but the decreasing rate is changeing�� During the unloading process��the fracture seepage velocity cannot be fully recovered to the size of the loading process�� Therefore��in the unloading process of the confining pressure��the recovery of fracture per- meability shows obvious hysteresis effects�� The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure�� In each cycle�� the evolution character of the flow rate with the confining pressure remains unchanged�� These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state��