DYNAMIC BEHAVIOUR OF RAILWAY BALLAST EXPOSED TO FLOODING CONDITIONS

Abstract

Railway ballast is one of the main components in ballasted railway track systems. It is
installed under the railway sleeper to absorb dynamic wheel/rail interaction forces, preventing the underlying
railway track subgrade from excessive stresses, enabling the interlocking of skeleton track onto the ground
and providing lateral track stability. Generally, the dynamic modeling of ballast gravels relies on the
available data, which are mostly focused on the condition at a dry condition. Recent findings show that
railway track could significantly experience extreme climate such as long-term flooding. This phenomenon
gives rise to a concern that the ballast may experience a higher level of moisture content than anticipated in
the past. On this ground, a test rig for estimating the dynamic properties of rail ballast has been devised at the
University of Birmingham. A non-destructive methodology for evaluating and monitoring the dynamic
properties of the rail ballast has been developed based on an instrumented hammer impact technique and an
equivalent single-degree-of-freedom system approximation. This investigation focuses on the dynamic
single-degree-of-freedom (SDOF) model of rail ballast submerged under the flood where the dependent
effects of frequency can be distinguished. Based on the impact-excitation responses, the analytical statedependent model was applied to best fit the experimental modal measurements that were performed in a
frequency range of 0-500 Hz. The curve fitting gives such dynamic parameters as the modal mass, dynamic
stiffness and dynamic damping constant, all of which are required for modern numerical modeling of a
railway track.