For the design and performance analyses of geosynthetic-reinforced soil structures under repeated loading, such as those induced by compaction, traffic and earthquakes, the understanding of cyclic soil–geosynthetic interface behaviour is of great interest. Nevertheless, experimental data concerning this type of behaviour are very scarce. A laboratory study was carried out and is described in this paper. This paper presents the behaviour of an interface between a silica sand and a high-strength geotextile under monotonic and cyclic loading conditions. A large-scale direct shear test device able to perform load- or displacement-controlled cyclic tests was used. The results obtained are presented and discussed, especially in terms of interface shear stiffness and damping ratio. Monotonic direct shear tests indicated that the coefficients of interaction for the sand–geotextile interface depend on the confining pressure. Cyclic direct shear tests indicated that the interface stiffness tends to increase during the first loading cycles, exhibiting slight variation after 10 cycles. Slightly higher values of shear stiffness and damping ratio were reached with displacement-controlled cyclic direct shear tests. The cyclic loading of the interface did not lead to the degradation of the post-cyclic peak shear strength; however, the post-cyclic shear strength for large displacements exhibited an important decrease.

The success of experimental studies to investigate hydraulics of dam breaching requires an adequate specification of geotechnical parameters and control over its realization in field or in laboratory conditions. Although this is known, there are few studies specifically addressed to formulate and discuss the requirements for comparable laboratory hydraulic tests to study embankment failure by overtopping. This study addresses this research gap specifically for homogeneous earthfill dams. It is aimed at proposing and discussing a set of core procedures and monitoring techniques to be observed in studies of dam breaching by overtopping. A first procedural step involves the theoretical discussion of similarities between model and prototype erodibility. Further steps involve observations of breached model dams under controlled hydraulic and geotechnical conditions. Requirements for comparability of hydraulic laboratory practice are described and discussed, and it is argued that the key geotechnical parameters of control are the soil composition (more specifically, the fraction of fine material) and the compaction conditions (relative compaction and water content). To attain similarity conditions in what concerns model dam erodibility, whose failure modes should include headcuts and undercutting, a range of reference values for the geotechnical control parameters is suggested and construction/compaction methods are discussed.