Stress distribution in roadbeds of slab tracks with longitudinal discontinuities

Abstract

Stress concentration occurs in the foundations of railway tracks where discontinuous components are located. The exacerbated stress under the expansion joints in slab tracks may trigger foundation failures such as mud pumping. Although the higher stress due to the discontinuities of track structures has been discussed in past studies, few focused on the stress response of roadbeds in slab tracks and quantitatively characterized the stress pattern. In this paper, we performed a dynamic finite element analysis of a track-formation system, incorporating expansion joints as primary longitudinal discontinuities. The configurations of CRTS III slab tracks and the contact conditions between concrete layers were considered. Numerical results show that longitudinal influencing length of induced stress on roadbed under wheel load relates to the contact conditions between concrete layers, increasing nonlinearly at a larger coefficient of friction. Given a measured coefficient of friction of 0.7, the calculated longitudinal influencing length (9.0 m) matches with field data. The longitudinal influencing length is not affected with the increasing velocity. As stress concentration arises with expansion joints, the worst-case scenario emerges when double-axle loads are exerted immediately above the expansion joints between concrete bases. A stress concentration factor Cv on the roadbed is proposed; it increases with the increasing velocity, changing from 1.33 to 1.52 at velocities between 5 and 400 km/h. The stress distribution on roadbeds transforms from a trapezoid pattern at continuous sections to a triangle pattern at points with longitudinal discontinuities. An explicit expression is finally proposed for the stress pattern on roadbed under expansion joints. Although structural discontinuities induce stress raiser, the extent of concentration is mitigated with increasing depth at different velocity levels.