Effect of short, randomly distributed polypropylene microfibres on shear strength behaviour of soils

An experimental programme was carried out on the shear strength behaviour of sandy and clayey soils reinforced with short, randomly distributed, polypropylene (PP) microfibres. The influence of fibre texture, fibre content, fibre length and normal stress level was investigated by means of direct shear tests. The best procedure to mix the soil with the fibres in order to achieve homogeneous and isotropic samples is described. This study shows that fibres increase the shear strength and significantly modify the shear stress displacement behaviour of the tested soils. Shear strength increases with increase in fibre content, fibre length and displacement. No appreciable advantage is achieved by using crimped (texturised) fibres as far as shear strength is concerned. Furthermore, mixture is achieved with greater difficulty when compared with straight fibres. There is an increase in both the apparent cohesion and the angle of shearing resistance of soils, owing to the short PP microfibres. The fibre contribution is especially significant for low normal stress levels. Despite the occurrence of some fibre damage, damaged fibres are still suitable for reinforcement.