Vibration Energy Transfer Mechanism in Ballastless Damping Track Structures Under Fastener and Damping Pad Failure Conditions

Laying rubber pads beneath ballastless tracks helps reduce substructure and environmental vibrations, but may amplify rail vibration owing to energy reflection. This study develops a coupled dynamic model of the ballastless track–rubber pad–subgrade system, with a focus on vibration energy transmission under fastener and damping pad failure conditions. An energy analysis based on power flow theory (PFT) is used to evaluate the system under harmonic excitation. The results indicate that fastener failure and damping pad failure significantly increase vibrational energy input to the rail and track slab in the low-frequency range (below 10–39 Hz). For example, at 30 Hz, rail power flow increases by 2.4 dB under single fastener failure and by up to 9 dB under consecutive failures. Failed damping pads (end or center) cause a power flow rise up to 15 dB around 65 Hz. In contrast, energy transmission to underlying layers (track slab, support layer, and subgrade surface) is reduced above 67–75 Hz, with decreases up to 35.6 dB in the subgrade under central pad failure. These shifts result from broken contact interfaces and compromised energy pathways. Therefore, selecting appropriate fastener stiffness and rubber pad stiffness is essential in the design of the ballastless track–rubber damping pad–subgrade system.