Improved Performance of Ballasted Tracks at Transition Zones: A Review of Experimental and Modelling Approaches

Track transitionssuch as bridge approaches, road crossings and shifts from slab track to ballasted track are common locations wheretrack degradation accelerates due to dynamic and high impact forces; as a consequence there is higher differential settlement. Thesetypes of discontinuities cause an abrupt change in the structural responseof the track due mainly tovariations in stiffness and track damping. Track transitionzones are prone to an accelerated deterioration of track material and geometrythat leads to increased maintenance costs.Track deteriorationalso leads to vehicle degradation due to enhanced acceleration, low frequency oscillation, and high frequency vibrations. While ballastdeterioration is amajor factor affecting thestability and longevity of rail tracks, the cost of tackling transitionrelatedproblems that detract from passenger comfort is also high.A good transition zone lessens the impact of dynamic load of moving trains by minimising theabrupt variations in track stiffnessand ensuring asmooth and gradual change from a less stiff (ballasted track)to a stiff (slabtrack) structure. This paper presents a critical review of various problems associated with transition zones and the measures adopted to mitigate them; it also includes critical review of research work carried out using large-scale laboratory testing, mathematical and computational modelling and field measurements on track transition zones