Sandwich Model to Evaluate Railroad Asphalt Trackbed Performance under Moving Loads

Abstract

Today, asphalt trackbed is gaining more attention because it effectively strengthens railroad track support, helps waterproof underlying sub-grade, and securely confines the subgrade layer. Traditional analytical track models are either quasi-static or based on a continuous support assumption, which does not consider nonuniform, discrete support due to varying tie and ballast service conditions. In this paper, a discretely supported track model with asphalt trackbed under dynamic moving loads was solved semianalytically. On the basis of this solution, a computer program was developed and applied to study, under different train speeds, the effect of track defects, such as broken tie and weak sub-grade, on asphalt trackbed service life. A case study analysis showed that all cases of faster train speed, weaker subgrade support, and missing tie support decreased asphalt trackbed fatigue life. Of the scenarios tested, missing tie support was proved to be the most critical factor that could dramatically decrease the trackbed fatigue life. Increasing asphalt trackbed thickness from 0.1 to 0.2 m significantly extended its fatigue life and also decreased subgrade stress. Although only limited situations are discussed here, the developed computer program based on the derived semianalytical solution can be used as an optimization tool for evaluating asphalt trackbed performances under various field conditions. It also has the potential for backcalculating dynamic track modulus when track deflections are measured.