By using the self-developed shear-seepage coupling test device for coal rock

experiments were carried out on similar materials containing structural surface sandstone to obtain shear-seepage coupling properties under different filling degrees. The results show that under constant water pressure

the larger the filling degree is

the smaller the peak shear stress of similar materials is

the larger the normal displacement is and shear shrink phenomenon is observed

and the larger the peak flow rate is within a certain filling degrees range. The flow change during shearing is mainly controlled by the cracks generated in the filling. The larger the shear displacement is

the more the fracture develops

and the greater the flow is. The normal displacement has a certain influence on the flow rate change

but with the increase of the filling degree

the influence becomes smaller. With the increase of filling degree

the fragmentation degree of filling materials gradually increases. The small filling degree is mainly controlled by the crack opening degree

while the large filling degree is mainly affected by the normal force. Due to the softening effect of permeate water

the wear degree of the structural surface slowly decreases.