Properties of rubber under-ballast mat used as ballastless track isolation layer in high-speed railway

Abstract

Rubber under-ballast mats (UBM) commonly used in metro traffic in China are applied in high-speed railway ballastless tracks as the isolation layer to improve the operating conditions of high-speed trains. Due to the different operating conditions between the high-speed railway and the metro traffic, the rubber UBM, used as the isolation layer in ballastless tracks, needs to be investigated furtherly. In this paper, a finite element analysis of the China Railway Track System (CRTS) III ballastless track was initially carried out, and the stress state and distribution of the rubber UBM used as the isolation layer were obtained at the service condition. Furthermore, the static, dynamic and fatigue tests of the rubber UBM samples were designed and carried out based on the analysis results. The main conclusions are as follows: under normal service conditions, the stress level of the rubber UBM is low, and it can be considered that the rubber UBM is still in the stage of linear elasticity. The material properties of the rubber UBM can be characterized by the equivalent elastic modulus, which has been determined to be 0.6 MPa by the experimental research. Furthermore, the dynamic characteristic of the rubber isolation layer exhibits a hysteresis phenomenon. The equivalent dynamic stiffness is larger than the equivalent static stiffness due to the viscoelastic characteristics of rubber material. The rubber UBM has large internal friction, high energy absorption rate and good damping performance characterized by its large loss factor. In addition, following the application of 3,000,000 repeated load, which is 1.5 times of a train axle load, the equivalent static stiffness only changes by 2%, indicating that the rubber UBM used as an isolation layer can maintain good mechanical performance under repeated loading. As such, the appropriate selection of rubber UBMs for the isolation layer in ballastless tracks can be made following the analysis and investigation of its performance characteristics.