Ground-Penetrating Radar Contamination Analysis Method Based on Time–Frequency Features and Ballast Condition

On heavy-haul railways, ballast fouling progressively reduces ballast resistance, which in turn degrades the electrical performance of track circuits. To address this cascading issue, we propose a ground-penetrating radar (GPR)-based method for assessing ballast bed conditions and inverting ballast resistance Rb continuously along the track. First, by integrating transmission line theory with Archie’s law, this paper establishes the mechanistic link between microscale dielectric deterioration of the fouled ballast and the macroscale electrical parameters of the track circuit. Next, we build a full-wave electromagnetic simulation model to extract two key GPR signal features: time-domain relative energy attenuation and frequency-domain spectral redshift. Recognizing the limitations of single-feature analysis, we introduce an adaptive weight-based multi-feature fusion algorithm to construct a comprehensive fouling index that quantifies the physical state of the ballast. Based on this index, we develop a quantitative mapping model between the fouling index (FI) and Rb, enabling continuous inversion of ballast resistance over the entire line. Our results show excellent agreement between the inverted Rb profile and the theoretical ground truth, with the FI alarm threshold precisely corresponding to the critical safety limit of Rb = 0.5 Ω km. This approach effectively overcomes the limitations of traditional discrete monitoring and provides a practical tool for predictive maintenance of track circuits.