Assessment of the Effect of Under-Ballast Mats on Vibration Reduction

Objective: development and substantiation of a computational and experimental approach to assessing the impact of under-ballast mats on reducing vibration in the track on railway lines, providing a transition from laboratory-determined characteristics of elastic material to the calculation of vibration transmissibility, insertion losses, dynamic stiffness and mechanical impedance of the “track–UBM– foundation” system. Methods: this paper examines existing viscoelastic models, vibration isolation assessment methods, and the requirements of DIN 45673, ISO 10846, and EN 17282. Standard and vibration isolation mechanical models of the track superstructure, as well as methods for calculating complex dynamic stiffness, transmissibility, and insertion loss in the frequency domain, are considered. For experimental evaluation, an indirect test method is proposed using a vibration rig with harmonic excitation, static preload, and recording of the displacement amplitudes of the support plate and loading mass. Results are processed using an equivalent single-mass model, which allows for the determination of the equivalent dynamic stiffness, damping coefficient, and mechanical impedance modulus based on the resonant frequency and peak width. An analytical impedance approach is proposed for the potential prediction of vibration impact, taking into account the ratio of the dynamic resistances of the track, mat, and foundation. Results: it has been established that the vibration isolation efficiency of under- ballast mat is determined not only by its dynamic stiffness and loss factor, but also by the system’s natural frequency and the impedance ratio of the structural elements. It has been shown that resonant amplification of vibrations is possible at frequencies below the natural frequency, while in the midand high-frequency ranges, the under- ballast mat reduces transmitted vibration. In the considered calculation example, positive insertion losses were obtained at frequencies above 33 Hz. The possibility of determining the equivalent dynamic stiffness, damping coefficient, and mechanical impedance modulus based on the amplitude frequency response obtained using two vibration transducers is substantiated. It has been determined that without measuring the phase shift or dynamic force, it is impossible to accurately determine the real and imaginary parts of the complex stiffness and complex impedance. Practical significance: the proposed approach allows the use of laboratory test results for under- ballast mats for preliminary calculations of insertion losses, determining the operating ranges of vibration isolation, and comparing materials in terms of dynamic stiffness and damping. The resulting equivalent characteristics can be used as input for a finite element model of a railway track.