A study is presented on the seepage flow occurring through homogeneous soil beneath
two structures in series separated by an intermediate filter with concrete blocks founded on two
pervious layers. The lower layer is of very high permeability than the upper one. The objective of
this study is to determine the effect of relative filter length, length of the filter/length of upstream
floor, provided with concrete blocks, on the seepage characteristics (uplift pressures under the two
floors and exit gradient downstream each structure). It's found that the increase in the relative filter
length causes a negligible effect on the relative uplifl; pressures under the upstream floor, a decrease
in the relative uplift pressures under the downstream floor, and a decrease in the exit gradient
downstream the downstream structure. It's reconomended to use a filter length of the same length of
the upstream floor. The concrete blocks are arranged with 20% perforated area and the block depth
is 25% of upstream floor depth