A Review of the Soil–Geosynthetic Interface Direct Shear Test and Numerical Modelling

The use of geosynthetics in reinforced soil structures (RSSs) requires the experimental and numerical modelling of the soil–geosynthetic interaction to support the design and analysis and deepen the knowledge of RSS systems. Direct shear testing has served as a fundamental laboratory choice for soil–geosynthetic interface testing, with the benefits being its availability, simplicity, and straightforward shear strength acquisition. This review paper pays attention to the direct shear testing and modelling of soil–geosynthetic interfaces. A brief laboratory interface experiment overview is presented, summarising the adopted soil–geosynthetic types, as well as the influences of various factors regarding soil–geosynthetic properties and loading/environmental conditions. Development of the finite element method to model interfaces is introduced, concentrating on the commonly adopted zero-thickness element, the thin-layer element, and continuum elements. As a result, emphasis is given to the comparison of the three element methodologies for the analysis of their advantages and limitations in accuracy, stability, and applicability for interface modelling. Based on the retrospective analysis, a summary and visions for the research progress of soil–geosynthetic interface testing and modelling are proposed to provide suggestions for future research topics.