# Qualitative Analysis of Sleeper Supporting Condition for Railway Ballasted Tracks Using Modal Test
###### Abstract  
During railway operations, changes in the support conditions of sleepers, owing to various internal and external factors, can damage rails and concrete sleepers and alter the structural characteristics of gravel-ballasted tracks. However, current methods for evaluating gravel ballast conditions primarily rely on visual inspection. This study proposes a quantitative approach using modal testing to assess ballast conditions. This is achieved by analyzing and experimentally verifying the relationship between track ballast loosening (caused by subgrade deformation) and track support performance. Finite element analysis results and field experimental values were compared using spring stiffness as a parameter. The results showed that natural frequencies and mode shapes changed in response to variations in the vertical spring stiffness of the gravel-ballasted track. Therefore, the steeper support condition of a gravel-ballasted track can be readily identified by analyzing the natural frequency corresponding to different sleeper support conditions. gravel-ballasted track; visual inspection; concrete sleepers; modal testing; subgrade deformation 2025  
25 February 2025 15 March  
Various researchers have contributed to understanding the dynamic changes associated with damage to concrete sleepers. [PERSON] et al. [2] applied modal testing techniques and impact hammer tests to study the dynamic characteristics of concrete sleepers. [PERSON] and [PERSON] [3] explored how boundary conditions affect the vibration characteristics of these sleepers, whereas [PERSON] [4] examined the influence of changes in material properties and rail pad stiffness on the free vibration characteristics of in situ concrete sleepers. [PERSON] and [PERSON] [5] employed impact hammer tests to assess the structural integrity of aging railway plate bridges and validated the reliability of these field tests through full-scale experimental modal analysis. Furthermore, [PERSON] and [PERSON] compared the outcomes of non-destructive impact hammer testing with those of visual inspections [6], whereas [PERSON] et al. and [PERSON] et al. investigated the potential damage to concrete sleepers [7; 8]. [PERSON] et al. determined, based on indoor testing and numerical analysis, that the primary type of damage to prestressed sleepers typically occurs directly beneath the rail [9]. [PERSON] et al. attributed sleeper damage to dynamic loads from train operations and exposure to climatic variations [10]. [PERSON] et al. [11] and [PERSON] [12] investigated damage types in concrete sleepers situated on the sharp curves of operational tracks, exploring how gravel replacement and sleeper renewal could mitigate this damage. Their findings indicated that axial cracks are prevalent, and improvements to the track structure significantly enhance load distribution, thereby reducing stress on the sleepers. [PERSON] and [PERSON] et al. employed numerical simulations to model gravel ballast and analyze track irregularities and the forces of wheel-rail interactions resulting from excavation activities on operational gravel-ballasted tracks [13; 14]. [PERSON] et al. [15] conducted both theoretical and experimental studies on sleeper support conditions using a mechanical model integrated with a data-driven approach. Their findings demonstrated that recent air gaps could be accurately identified by extracting wavelet scattering features from trackside measurements using machine learning techniques. [PERSON] et al. [16] examined the effect of sleeper support modulus on the dynamic behavior of railway tracks caused by moving wagons, employing both numerical simulations and field tests. Their results indicated a strong agreement between the numerical analysis and field measurements. Similarly, [PERSON] et al. [17] investigated the dynamic properties of railway ballast mixed with tire-derived aggregates using modal shaker tests.