Abstract
This paper presents the development of a rational design method for determining the formation thickness of a railroad track. The design method is based on keeping the maximum deviator stress induced on the subgrade surface due to traffic loading below the threshold stress of the subgrade soil by providing a suitable formation thickness. The design method is intended to achieve a stable deformation behavior of the subgrade soil under repeated loading, limiting plastic deformation. The new method has significant advantages over existing methods. The new method is applicable to various soil types, and different ballast and subballast qualities. The effect of the rail size and the tie spacing is separated from the formation quality and design charts for different values of rail size and tie spacing can be readily prepared. A simple laboratory test procedure for quick evaluation of the threshold stress of the subgrade soil is suggested. A flow chart is given for systematic formation design along with a suitable design example. The importance of drainage condition for the success of this approach is emphasized. The design method is evaluated by observing the performance of an actual track under repeated load applications.
