The present study is intended to investigate the effect of the sub-layers formation on seepage characteristics (uplift pressure, seepage discharge and hydraulic gradient). This objective is fulfilled through studying a hydraulic structure founded upon two horizontal layers with different arrangement and relative thickness. The study is carried out experimentally by using the sand model technique and numerically by using the boundary element method. The results indicate that, the decreasing of the permeability of the lower sub-layer causes an increasing in the values of the uplift pressure, an increasing in the hydraulic gradient, and a decreasing in the seepage discharge. Both the experimental and the numerical results show reasonable agreement in comparison with published results. A solved example is considered to illustrate the use of the obtained charts.