Experimental investigation on static and dynamic characteristics of granulated rubber-sand mixtures as a new railway subgrade filler

Because of their low unit weight, strong linear elastic deformation ability, good durability and high energy dissipation, mixtures of waste tire rubber and sand have been increasingly used as a new type of subgrade filler in railway engineering. To investigate static and dynamic characteristics of granulated rubber-sand mixtures as a new filler, consolidated undrained monotonic and cyclic triaxial tests were carried out. The monotonic triaxial tests reveal that the shear strength of mixtures first increases and then decreases with increasing granulated rubber content and is maximized when the rubber content is approximately 10%. Based on the theory of an equivalent intergranular void ratio, a new equation for estimating the peak deviatoric stress of mixtures is proposed. The cyclic triaxial tests reveal that the addition of granulated rubber can constrain the generation and accumulation of dynamic pore water pressure and improve the liquefaction resistance of mixtures. The change in shear modulus is inversely proportional to the change in granulated rubber content and frequency, and directly proportional to the change in confining pressure. A new equation is also established for calculating the maximum shear modulus considering the effect of the equivalent intergranular void ratio and confining pressure. By comparing the maximum shear modulus of the new railway subgrade filler with that of other subgrade filler, it is concluded that a granulated rubber content of less than 20% can meet engineering requirements related to shear stiffness. The damping ratio is correlated with granulated rubber content, negatively correlated with confining pressure and insensitive to loading frequency. The relationship between the damping ratio and shear strain conforms to the equation proposed by Hardin and Drnevich. Based on the analysis of static and dynamic characteristics of granulated rubber-sand mixtures with different rubber content, the optimum granulated rubber content should be approximately 10%. (C) 2020 Elsevier Ltd. All rights reserved.