Strain rate effect of frozen ballast aggregates under compression: Experiments and discrete element simulations

Abstract

Ballast railway tracks in cold regions are typically affected by severe freezing damage. To further investigate the mechanical properties of the ballast layer under freezing conditions, ice–bonded ballast specimens are prepared, and uniaxial compression tests are performed in a low-temperature environment. The effect of strain rate on the stress–strain curve, failure mode, and compressive strength are discussed comprehensively under two ice content ranges. Meanwhile, a dilated polyhedron discrete element method based on bonded particle model (DP-DEM-BPM) was developed to establish the discrete element model of ice–bonded ballast under uniaxial compression. The results show that the strain rate significantly affects the deformation characteristics of the frozen specimens. When the strain rate is low, the stress–strain curves exhibit clear strain-softening characteristics. As the strain rate increases, the post-peak stress decreases more rapidly, and the brittleness becomes more prominent. Meanwhile, the strain rate can be categorised into ductile, ductile–brittle transition, and brittle zones based on the stress–strain curve and failure mode. The specimens in the ductile zone primarily present axial splitting failure, whereas those in the brittle zone present brittle fracture with multistage local crushing. The corresponding discrete element simulation reveals the internal mechanism of failure modes in the specimen from the point of view of the bond. In addition, the uniaxial compressive strength and effective elasticity modulus increase in the ductile zone and then decrease in the brittle zone as the strain rate increases. The relationship between compressive strength and strain rate can be expressed using a piecewise function.