Discrete framework for limit equilibrium analysis of fibre-reinforced soil

A methodology is proposed for the design of fibre-reinforced soil slopes using a discrete framework. The analysis of fibre-reinforced soil using traditional composite approaches requires the implementation of laboratory testing programmes on composite fibre-reinforced soil specimens to characterise the material properties. Instead, the analysis of fibre-reinforced soil using a discrete approach can be conducted by independent characterisation of soil specimens and of fibre specimens, since the contributions of soil and fibres are treated separately. A fibre-induced distributed tension can be defined for use in limit equilibrium analysis using the proposed discrete framework. The fibre-induced distributed tension is a function of the volumetric fibre content and tensile strength of individual fibres when failure is induced by fibre breakage. Instead, when failure is induced by fibre pullout, the fibre-induced distributed tension is a function of the volumetric fibre content, interface shear strength and fibre aspect ratio. A critical normal stress, which defines whether the reinforced soil behaviour is governed by pullout or by breakage of the fibres, can be defined analytically using the proposed framework. An experimental testing programme involving tensile testing of fibres as well as triaxial testing of unreinforced and fibre-reinforced specimens was undertaken to validate the proposed framework. As predicted by the discrete framework, the fibre-induced distributed tension was observed to be proportional to the fibre content and fibre aspect ratio when failure was characterised by pullout of individual fibres. The discrete framework predicted accurately the contribution of randomly distributed fibres for the various soil types, fibre aspect ratios and fibre contents considered in the experimental testing programme.