A constant normal stiffness direct shear box for soil-solid interfaces tests

The paper deals with the results of interface tests conducted on a modified direct shear box apparatus, under constant normal load (CNL) and constant normal stiffness (CNS) conditions. Tests have been carried out on different types of interfaces each one consisting of an aluminium plate with a specified roughness surface in contact with a silica sand. Three different sands have been investigated. For sake of brevity only the results concerning two extreme types of interfaces for all sands have been described in detail, namely a dense rough interface (D/30) and a loose smooth interface (L/3). A description of the apparatus is provided and the factors affecting the reliability of the tests are analysed. Typical test results are shown and the influence of the “confined dilatancy” on the two different types of interfaces is discussed.