The effect of polypropylene fibre content on the mechanical properties of mass-stabilised soils

Mass mixing or deep soil mixing involves cement being used as a binder within a weak or soft soil, with scope to turning it into a stable foundation. In this study, we investigate the effect polypropilene fibres have when introduced within a mass stabilised soil in order to improve the soil strength and potentially be used in production of pipework, bricks, insulation, window frames, or as a substitute to bitumen acting as a binder. In order to investigate this, polypropylene fibres were added to a soil mix originating from a site in the Scottish Central Belt. The fibres were added at different contents (0%, 0.5% and 2%) and lengths (3mm and 12mm), they were then put through a series of laboratory tests (direct shear, unconfined compressive strength and oedometer consolidation) at an accredited soil testing laboratory. The data obtained from the tests show that there is a significant strength gain if polypropilene fibres are added in large quantity. However, these strength levels are achievable at relatively high strains. The results also show that the volume compressibility of the soil reinforced with plastics increases with the polypropilene fibre content, although this may depend on the length of the fibres mixed in the soil. In conclusion, the polypropilene fibres do showcase a much more ductile failure compared to the soil only, which could possibly be used and have some limited benefits. Further testing of different plastic additions and soil mixes should be carried out to explore other effects.