Experiments of water infiltration in a vertical plane through layered soils were carried out in the laboratory. We have followed the fingering dynamics by using image techniques. The fractal theory has been applied to describe the fingering phenomena. We also have simulated a modified site gradient invasion percolation model where most of the physical ingredients relevant to the problem have been incorporated. In contrast to what occurs with the standard gradient invasion percolation model, we have found the formation of many fingers. Taking into account the bond number, the number of fingers, and the wetted area of the experiments, we have fitted the parameters of our model. This opens the possibility of a theoretical prediction of the pore size distribution of the soil. The results are then compared with the experimental data. (C) 1995 American Institute of Physics.