Fibres and roots for soil improvement

Paper in proceeding, 2015

Observing the experimental interaction of flexible fibres and granular soils provides inspiration for the development of continuum models for the behaviour of fibre/soil mixtures. The detailed experimental observations come from mixtures of sand with flexible polypropylene fibres but the principles are believed to be relevant also for soils containing flexible plant roots. Two features are particularly important: the distribution of orientations of fibres (no method of preparation produces an isotropic distribution) and the allowance for the volume of void space not only occupied but also influenced by the presence of the fibres. As the soil-fibre mixture deforms, the straining of the soil generates fibre stresses in favourably oriented fibres. A simple shear element is used as a quasi-one-dimensional demonstrator platform for the development of this model. Pedagogically such an element has a number of desirable benefits: it represents a familiar configuration in which phenomena such as dilation and friction can be directly observed; and it is straightforward to convert the model for application to axisymmetric or general stress conditions.