Method for Railroad Track Foundation Design. I: Development

This paper presents the development of a new design method for selecting granular layer thickness for railroad track. Design of an adequate granular layer thickness is intended to prevent two common railroad subgrade failures due to repeated traffic loading. One type of subgrade failure is progressive shear failure, and the other is excessive plastic deformation. The design is based on limiting traffic load-induced deviator stress in the subgrade, which represents the combined influence of both vertical and confining stresses, to levels producing acceptable subgrade performance. The new method has significant advantages over existing methods. These advantages include the way in which traffic is characterized, the multilayer representation of the track structure, and emphasis on subgrade performance under repeated loading. Design charts developed cover various soil and granular layer conditions. The soil and granular properties considered include resilient modulus, soil compressive strength, and soil type. The traffic is characterized by the dynamic wheel loads and the total equivalent number of repeated load applications for the design period.