Experimental and numerical evaluation of lateral stability of ballasted railway track under loosened ballast and localized ballast loss conditions

Abstract

Thermally induced track buckling in continuous welded rail (CWR) systems occurs primarily when the lateral ballast resistance (LR) fails to counteract accumulated compressive forces. Natural hazards can generate ballast defects that modify both LR and buckling behavior of the track structure, thereby compromising its overall lateral stability. To investigate the LR and buckling behavior of ballasted railway tracks under typical ballast defects, this study conducted both single-sleeper pullout tests (SSPTs) and track panel pullout tests (TPPTs) on 1/9-scale railway models, complemented by numerical simulations. Two types of ballast defects were considered: loosened ballast and localized ballast loss (characterized by the local ballast loss ratio (LBR) up to 100 %). First, SSPTs were performed to assess the effects of both the ballast defect types on the LR of single sleepers. The obtained nonlinear lateral load–displacement curves were fitted using both conventional bilinear method and improved piecewise nonlinear method incorporating the initial static friction. Subsequently, a ballasted track model consisting of 21 sleepers was constructed for the TPPTs to evaluate their overall lateral stability under ballast defects. A corresponding simulation model based on a spring-beam system was developed. A comparison of the two fitting methods with the experimental results under intact and loosened ballast conditions revealed that the improved nonlinear method provided superior accuracy in representing the LR and predicting track buckling behavior. Furthermore, by employing the improved nonlinear method, the influence of localized ballast loss was investigated systematically under two groups: (i) five consecutive central sleepers with varying LBR and (ii) multiple consecutive sleepers exhibiting complete ballast loss. Key indicators (including the cumulative work under lateral loading (E) and accumulated deformation (W) derived from the integral of lateral load and integral of buckling profile of tracks) were calculated to assess the lateral stability of the track. The results demonstrate that static friction contributes significantly to the LR under intact ballast conditions. As the lateral loading progressed, E and W exhibited an approximately linear relationship, with intact ballast requiring a higher E to generate an equivalent W. As the ballast density decreased or localized ballast loss increased, E_1mm decreased, and W_1mm increased. Overall, the proposed experimental and simulation methods effectively predicted the lateral resistance and buckling behavior of track models affected by ballast defects.