Experimental study of the effect of boundary layer on the solute transport in a rough single fracture

To explore the phenomena of early peak arrival and trailing of non-Fickian migration, the solute migration experiment of a rough single fracture is carried out, the solute migration characteristics and migration mechanism in the rough single fracture are summarized, and the phenomena of early peak arrival and trailing are analyzed and explained in combination with the boundary layer theory. The results show that there is a good linear correlation between the peak arrival time, the trailing time and the thickness of the boundary layer; The boundary layer has a significant effect on the solute transport in fractured media, that is, the smaller the flow velocity is, the greater the thickness of the boundary layer is, the more solutes remain in the boundary layer, and the lower the solute acquisition rate is; the peak advance and trailing of solute penetration curve in the rough single fracture are caused by the joint action of the main flow area dominated by the inertial force in the fracture center and the boundary layer area dominated by the viscous force on the fracture wall. Among them, the peak arrival time is mainly controlled by the convection factor in the main flow area and the existence of the boundary layer area has a great influence on the trailing time.