Some of the most sustainable and economical benefits of using geosynthetics are found in reinforcement applications. These applications allow the use of lower quality on-site material such as fine grained soils often referred to as ‘marginal fills’. This paper identifies the state of practice and understanding of designing with these soilsin applications such as embankments, slopes and retaining walls. Designers often rely on published guidance documents and the paper discusses the influence BS 8006 (2010) has on the use of  ‘marginal fills’ in construction and how the need for clearer more specific guidance. The study highlightsthat often well compacted fine grained fills placed close to optimum moisture content generate suctions, and this results in relatively high strength interaction between the fill and geosynthetic reinforcement. In cases where a fine grained fill with high moisture content is used, geosynthetic reinforcement that provides in-plane drainage may be beneficial.