Influence of ice-bonded ballast on rail break gap size: A laboratory and finite element model investigation

Sub-freezing temperatures result in ice formation within the ballast layer of railroad track. Given the proper moisture and fouling conditions, the retained moisture bonds ballast particles together changing the mechanical properties. In temperatures above freezing, longitudinal track resistance ( f 0 ) to restrain the track system has been quantified by crosstie-type and ballast condition (e.g., consolidated or disturbed). Sub-freezing temperatures produce the largest differentials between the rail temperature and RNT (rail neutral temperature) [i.e., differential temperatures (dTs) exceeding 30°C (100°F)] producing tensile stresses that can exceed the strength of the rail at defects, causing the rail to break and a gap to open. This study quantified the effect of frozen ballast on shear strength, f 0 , and rail gap size using laboratory experimental data and Illi3D, a field-validated finite element model (FEM). The laboratory data was transformed into f 0 using a novel method developed in this study and then incorporated into Illi3D to simulate single rail breaks and quantify the effect ice-bonded ballast has on rail break gap. Clean and fouled-ballast shear strengths exhibited different behaviors when frozen. The f 0 of fouled-frozen ballast increased two to five times, and the gap size reduced 76% and 56% for timber and concrete crosstie track, respectively.