In order to study the shear-flow coupling characteristics of joints under constant normal stiffness (CNS) boundary condition

the shear-flow coupling tests under three different stiffness and seepage pressure settings were carried out for duplicate joint specimens with three different joint roughnesses. Meanwhile

the effects of normal stiffness

seepage pressure and joint roughness on the mechanical properties and seepage characteristics in joint shearing process were systematically analyzed. The test results indicate that the peak shear strength of joint increases with the increase of normal stiffness

while the flow rate

equivalent hydraulic aperture and transmissivity decrease with the increase of normal stiffness; and the flow rate of seepage through joint surfaces during shearing process decreases with the increase of joint roughness. A three-stage change rule of flow rate that is similar to the joint dilatancy is shown in the shearing process: rapid growth stage

slow growth stage

and stable stage. The same rule has also been observed in equivalent hydraulic aperture and transmissivity. During the stable stage

the flow rate is approximately linear with the variation of the normal stiffness and seepage pressure

and the joints with higher roughness present lower flow rate as the seepage pressure increases.