Transition of railroad bridge approaches

Years of investigations have shown that very stiff track structures on railroad bridges and abrupt stiffness changes between the bridge and the approach are two factors that can accelerate the performance problems associated with concrete tie track, ballasted deck concrete bridges. These problems include rapid track geometry degradation and cracking of concrete ties. For the four sites investigated, the resulting geometry degradation (or differential settlement between bridge and approach) came from the ballast and subballast layers, with additional contribution from the underlying soil layers (subgrade). Remedies intended to strengthen the approach subgrade may not be effective, if they are not designed to produce consistent and acceptable track stiffness between the bridge and the approach. The study presented in this paper was conducted on a number of railroad bridges and their approaches on a western railroad in the United States. The objective of the study was to investigate the factors that can cause or accelerate performance problems associated with bridge approach or track transition, and to identify and evaluate appropriate mitigation methods.