Cyclic and post-cyclic shear behaviours of natural fibre reinforced soil

Soil behaviour under cyclic loading is a key component in assessing potential effects of earthquakes on infrastructure and the response of earth structures to dynamic loading. In this study, cyclic and post-cyclic shear behaviours of fibre reinforced and unreinforced soil were investigated. Series of undrained cyclic triaxial tests were performed to study effects of sisal fibres of 25 mm length and contents of 0.25%, 0.5% and 1% on the shear modulus, damping ratio, permanent strain, cumulative strain and liquefaction potential. The post- cyclic shear tests were conducted to study effects of fibre inclusion on the post cyclic energy absorbing capacity, toughness and static energy ratio. The results showed that fibre inclusions caused an increase in shear modulus to a limiting fibre content of 0.5% beyond which modulus reduced. The reduction was attributed to the loss of stiffness of soil composite due to high amount of voids. Fibre inclusions increased damping ratio due to enhanced resistance to deformation. Both permanent and cumulative strains reduced with fibre inclusions as a result of an increase in the resilience of soil composites to deformation. Both reinforced and unreinforced soil types exhibited high resistance to liquefaction. Increasing fibre content caused an increase in the post cyclic energy absorbing capacity, toughness and static energy ratio of the soil composite.