Influence of geogrid stabilization on ballast breakage under monotonic triaxial loading

Railway ballast particle breakage leads to fines generation, increases fouling, reduces drainage capacity, and ultimately weakens track performance. While geogrids are known to stabilize ballast by limiting particle movement and redistributing contact stresses, their effectiveness in reducing breakage, particularly at different ballast depths, remains unclear. This study employs a large-scale monotonic triaxial testing framework to evaluate particle breakage in clean ballast, with and without geogrid stabilization, under both loose and compacted density conditions. Each specimen was divided into four vertical zones: Top , Top-Mid , Bottom-Mid , and Bottom , and particle size groups were color-coated to enable breakage tracking. The results show that geogrid-stabilized specimens exhibited greater strength and stiffness in both density conditions. For loose ballast, geogrid inclusion reduced total particle breakage by approximately 27%, with the most significant reduction occurring in the middle zones. In contrast, for compacted ballast, the total breakage remained nearly unchanged with geogrid use; however, breakage was more evenly distributed across all zones, with noticeable reductions in the Top and Top-Mid zones. Corner breakage dominated in the middle zones, and splitting breakage near the top and bottom. Marsal’s breakage (B g ) index proved most sensitive for zone-by-zone evaluation. The findings highlight the benefit of geogrids in mitigating ballast degradation and emphasize the importance of zone-specific analysis under varying density conditions. The proposed monotonic triaxial framework provides a mechanistic baseline for future cyclic triaxial studies, where repetitive loading will further clarify long-term stress redistribution, particle migration, and cumulative breakage under realistic railway service conditions.