Application of Multi-laminate Model to Analyze the Influence of Principal Stress Rotation Stress Paths on Permanent Deformation of Railway Ballast

Moving trains cause significant amplification of dynamic stresses in the shallow track layers. Under these stresses, railway ballast undergoes exacerbated permanent deformation and degradation that will eventually increase the maintenance costs of railway track. In addition to stress amplification, stress paths are also affected by moving train loads due to the rotation of principal stress axes. In this paper, the influence of different principal stress rotation (PSR) stress paths on permanent deformation response of ballast are analyzed using a multi-laminate constitutive model. The constitutive model is calibrated and validated with the laboratory tests on ballast under triaxial compression stress paths and extended to PSR stress paths. The PSR stress paths are quantified using a new modified cyclic stress ratio (CSR*) which incorporates the effects of both load amplification and principal stress rotation. The model predictions show that permanent deformations increase with CSR* and vary with changes in stress path even when cyclic loading amplitude remains constant. When PSR stress paths are considered, the permanent deformations amplify at a higher rate than for the cases without PSR. Further, the shakedown response of permanent deformations under PSR stress paths is investigated based on the model predictions.