Dynamic characteristics of frozen ballast beds in cold-region railways under cyclic train loading.

Due to the freezing influences in alpine regions, an in-depth study of the dynamic characteristics of frozen ballast beds is urgently needed. This paper established discrete element method (DEM) models incorporating ballast-ice bonding, validated through laboratory cyclic loading tests, uniaxial compression tests and vehicle-track coupled dynamics (VTCD). Using the validated models, the effects of varying ice contents on cumulative settlement, bearing stiffness, particle movement, coordination number, number of ice bonding keys, and force chain evolutions were investigated. The results show that high ice content significantly inhibits cumulative settlement, with stabilization typically after 200 loading cycles. The average coordination number, number of ice bonding key, and bonding failure rate all exhibit pronounced segmented changes, with ice content 20% as a key value. Freezing drives the transfer mechanism of internal load from “particle force chains” to “ice-bonded blocky aggregates”. The average coordination number increases markedly with rising ice content, reflecting a structural evolution from a loose granular skeleton to a dense frozen network. These mesoscopic mechanisms directly control the macroscopic dynamic responses by elevating the ballast bed stiffness, localizing particle motion beneath the sleeper, and suppressing overall settlement.