Effects of Stress History on Ballast Deformation

The behavior of densely prepared specimens of a crushed dolomite railroad ballast subjected to triaxial compression repeated loading at a constant effective confining stress of 35 kN/m² (5 psi) is reported. The effects of the magnitude of the applied stresses and stress history are observed in the resulting permanent deformation. It is found that this characteristic was influenced significantly by the magnitude and order of application of the applied stresses. Stresses less that about 50% of the static failure stress are found to have negligible effect in conditioning the ballast for subsequent higher stresses. On the other hand, the application of a high stress prior to a smaller stress (50% of high stress) and progressively increasing stresses up to 82% of the static failure stress are found to result in negligible increases in plastic deformation and reduction in the rate of accumulation of plastic deformation, respectively.