Influence of clay fraction on the shear behavior of an interface between sand-clay mixture and concrete

In geotechnical engineering, the soil-structure interface is an important aspect to be taken into account in soilstructure interaction because it relates to the stability of supported structure. In particular, the shear behavior of the soil-structure interface plays a key role in the design of civil engineering structures and their analysis over time. The interface is a thin zone of soil in contact with the structure where major stresses and strains develop in. To our knowledge, previous works on the characterization of the mechanical behavior of the soil-structure interface mainly include typical soils (sand or clay) or natural soils, in contact with variable structural materials (concrete, steel, wood). However, natural soils are very complex, partly due to geological heterogeneities, and the mechanical response of typical soils does not always represent accurately intermediate soils between sand and clay. Previous studies on the mechanical behavior of those soils are significantly represented in the literature, especially in experimental research, however it is rather poorly documented on the interface between these soils and structural materials, whereas their response to mechanical loadings is different. The objective of this paper is to characterize the shear behavior of the soil-structure interface for intermediate soils between sand and clay, by experiments at the laboratory scale. Artificial mixtures of silica sand and kaolinite-rich clay are chosen to represent the intermediate soils in this study. For this propose, the research is organized in a main experimental campaign that aims to investigate the effect of the clay fraction, from 0% (sand) to 55% (kaolin clay) on the mechanical behavior of a soil-concrete interface by a direct shear device in the laboratory. The characterization of the shear behavior of the soil-concrete interface at various clay and sand fractions allows to enlighten the role of soil microstructure at the soil-structure interface on the stability of civil engineering structures.