Shakedown Limit Analysis of Layered Slab Track Substructures

ABSTRACT Shakedown analysis provides a mechanistic criterion for evaluating the long‐term stability of geomaterials subjected to infinite loading cycles, such as those induced by highways and railways. This study focuses on prefabricated slab tracks in high‐speed rail and introduces a computational method that explicitly considers stress responses at two critical locations: structural expansion joints and continuous slabs. Although expansion joints have occasionally been mentioned in prior studies, their role in shakedown analysis has not been systematically investigated. Addressing this gap, the present work extends the analysis to better reflect actual service conditions of slab tracks. By superimposing computed stress fields with self‐weight stresses, shakedown analyses of a two‐layer subgrade system were performed under varying soil parameters, following Melan's lower‐bound theorem. Results show that the trackbed surface is the most critical stress location. When the surface friction angle increases from 30° to 60°, shakedown capacity improves by about 32%, demonstrating that enhancing soil strength can significantly extend slab track design life. In contrast, increasing the stiffness ratio between the surface and bottom layers markedly reduces shakedown capacity, highlighting the importance of controlling stiffness contrasts within the subgrade. Thickness ratio variations also influence capacity, though less strongly. For practical application, a simplified closed‐form solution is proposed to estimate the bounds of shakedown axle loads at different train speeds. Overall, this study quantifies the sensitivity of shakedown capacity to key soil parameters and demonstrates that expansion joints play a pivotal role in governing track performance, thereby guiding safer, more durable slab track subgrades.