Material Selection for the Design of inclined Covers with Capillary Barrier Effect

A design procedure is proposed to select landfill cover materials. The specific case of inclined covers that limit infiltration due to the capillary barrier effect is investigated. A well known model for the calculation of the diversion capacity is employed. Material selection is mainly based on hydraulic conductivity functions (k-functions). The capillary break layer (CBL; bottom layer) of an ideal inclined capillary barrier should include a material within which capillarity forces are as weak as possible for the infiltration rate considered, whereas the moisture retaining layer (MRL; top layer) must be capable to develop the strongest capillarity forces possible, for the same infiltration rate. In addition, the MRL must be as permeable as possible, so that water is efficiently drained downslope and out of the cover. Application of the proposed procedure shows that a combination of coarse materials (such as sand over gravel) diverts water over greater lengths than barriers employing fine-grained materials as MRL.