Abstract: The method of incorporating tire-derived aggregate (TDA) into ballast not only has the advantages of reducing ballast crushing and vibration but also alleviates the increasing pressure of waste tire disposal. Due to its energy-saving, eco-friendly characteristics, among others, it has increasingly attracted the attention of researchers. However, current research primarily focuses on the effect of TDA content through laboratory tests, with relatively little research on the influence of other parameters. Particle shape is a crucial factor influencing the mechanical properties of granular geomaterials. Studying the dynamic properties and meso-effects of mixtures containing different shapes of TDA is a necessary foundation for enhancing our understanding and promoting the application of these methods. Based on the same TDA content and specimen void ratio, block, elongated, and flat TDA particles were mixed into ballast, and dynamic triaxial tests and discrete element simulations were conducted to compare and analyze the macro-level test results and meso-level effects of the ballast samples. The results show that the cumulative axial strain of ballast mixed with elongated and flat TDA is smaller than that of pure ballast, while the cumulative axial strain of ballast mixed with block TDA is larger than that of pure ballast; the reduction in dynamic elastic modulus caused by elongated and flat TDA is also smaller than that caused by block TDA. The dissipative energy and damping ratio of ballast mixed with elongated TDA are larger and develop stably. The damping ratio of ballast mixed with flat TDA is relatively small and gradually decreases with the number of loadings. Due to their shape characteristics, elongated and flat TDA primarily increase the coordination number between rubber particles, making the aggregate denser. Elongated and flat TDA can significantly inhibit the rotation speed and cumulative rotation angle of the particles, thus reducing the cumulative deformation of the samples

Key words: tire-derived aggregate shape, ballast, triaxial test, discrete element