Cyclic shear stress degradation and post-cyclic behaviour from sand–steel interface direct shear tests

The sliding interaction between sand and structural materials is involved in many geotechnical applications and is particularly important for the derivation of the shaft capacity of piles. Such interaction develops principally at the interface between the sand mass and the structural surface, and the comprehension of such interaction can be analysed through soil–structure interface tests. In particular, by using a modified version of the interface direct shear apparatus, that is, the constant normal stiffness direct shear apparatus, the friction characteristics of the interface and the role of the soil deformability on the experimental results can be studied. This paper focuses on the stress degradation occurring in these types of tests when cyclic loading is applied on sand–steel interfaces. Also, the post-cyclic response is analysed and compared to the response under monotonic conditions.Key words: interface, sand, shear stress, cyclic loading, stress degradation.