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A laboratory study was undertaken on the transport and the deposition of suspended particles (silt of modal diametre 6 µm) in three columns of different length, filled with glass beads or gravel. Tracer tests were carried out at various flow velocities by short pulses of a mixture of suspended particles/dissolved tracer. The breakthrough curves were competently described with the analytical solution of a convection dispersion equation with a first-order deposition rate and the hydro-dispersive parameters were deduced. For the same experimental conditions, the results showed a difference in the behaviour of the suspended particles transport and deposition rates within the two porous media tested. The internal structure of both media governs the particle-grain collision frequency as well as the particles trapping. The scale effect was highlighted and affects the dispersivity, the size exclusion effect, the recovery rates and the deposition rates. Longitudinal dispersion increases with mean pore velocity and is described with a nonlinear relationship. The dispersivity increases with the column length. The size exclusion effect is more important in the short column. The recovery rate increases with flow velocity and decreases while increasing column length. The deposition rates increases until a critical flow velocity then decreases. This critical velocity is also sensitive to the scale effect, and increases with the column length.

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International audienceThis paper discusses the transport and deposition rate of suspended particles in saturated porous media. The laboratory study used a column where the porous media were subjected to a steady state flow. Two materials were used: gravel and glass beads. Silt particles of 14 µm mean diameter were used as suspended particle tracer. By means of short pulse injection, transport tests using suspended particles and a conservative tracer were performed. The breakthrough curves were well described with the analytical solution of the convection-dispersion equation with first-order deposition rate. The experiments were performed under different flow rates. The particle size distribution, the porous media, and the flow rates tested were the main factors retained in this study to investigate the mechanisms governing the transport and deposition kinetics. The results showed the existence of a flow rate beyond which suspended particles travel faster than the conservative tracer. A decrease of the deposition rate of suspended particles beyond a critical flow velocity is observed too. Such behaviour makes us think of the couple hydrodynamic-gravity forces at high flow rates. As the hydrodynamic force increases particle deposition rates are reduced due to the effect of hydrodynamic forces inhibiting the deposition

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