Experimental investigation of heavy haul railway embankment deformation under traffic-induced bi-directional principal stress rotation

Heavy haul railway line infrastructure, essential for land freight transportation, subjects its foundation soils to complex stress paths under cyclic traffic loads, including bi-directional principal stress rotation (PSR), a critical yet under-researched phenomenon. Conventional research, constrained by experimental limitations, predominantly focuses on uni-directional PSR, risking underestimation of long-term soil deformation induced by cyclic traffic loads. This study addresses this gap by first employing finite element simulations to characterize stress paths, particularly bi-directional PSR, in soil beneath a single-track heavy haul railway. These stress paths guide subsequent bi-directional dynamic simple shear tests on Leighton Buzzard sand, analyzing axial and shear deformation and axial resilient modulus under bi-directional PSR. Results reveal that bi-directional PSR induces greater vertical deformation compared to uni-directional conditions. In particular, vertical deformation at off-centerline locations near the rail may exceed that at the centerline. These findings advance the predicting accuracy for long-term deformation in heavy haul railway embankments induced by cyclic traffic loads, emphasizing the necessity of incorporating bi-directional PSR effects to enhance design and maintenance procedures.