The effect of soil on the shear strength of geosynthetic interfaces

In landfill cover systems, a geogrid or reinforced geomat is often used, placed just above the upper drainage geocomposite, to ensure the stability of the topsoil. In these cases, a specific interface occurs, which could be defined as a mixed interface, as there is a simultaneous contact between two geosynthetics and between the geosynthetics and the soil. The paper presents some preliminary results of a research on the interface shear strength of two interfaces of this type, corresponding to the contact between a drainage geocomposite and a geogrid or a reinforced geomat. A series of tests were carried out with a not standard direct shear device, operating at increased shear stress, to compare the response of the soil-less interface with that measured in the presence of the soil. The results showed how the presence of soil leads to an increase in the shear strength compared to the condition without soil and they also highlighted how the influence of soil on the behavior of the interface depends on the type of reinforcement used.