Sand reinforced with short polypropylene fibres has been tested in conventional triaxial compression and extension. The contribution of fibres to the strength was remarkable in compression while limited in extension confirming that it depends primarily on their orientation with respect to tensile strains. A modelling approach is proposed for coupling the effects of fibres with the stress-strain behaviour of unreinforced soil. It is necessary to define a fibre stiffness matrix and in this investigation it is assumed that fibres are working in their elastic domain. Any distribution of fibre orientations can be accounted for. The sand stiffness matrix is based on the Mohr Coulomb model although more elaborate models could be used. The constitutive model for the fibre-sand composite is calibrated against the results of drained triaxial compression and extension tests. Despite the simplistic nature of the Mohr-Coulomb assumptions for the sand matrix, simulations show how the influence of fibre orientation with respect to the strain conditions is captured and provide good agreement with experimental data. (C) 2009 Elsevier Ltd. All rights reserved.