Track Foundation Parameters and Their Interrelation

There is ongoing confusion among track professionals regarding various track foundation parameters, which are often labeled differently (such as track modulus, support stiffness, track stiffness, mean track stiffness, total spring constant, spring constant, characteristic length, etc.) and their relationship with each other. These terms are frequently used interchangeably by different authors in North America and Europe, leading to potential misunderstandings. To address this issue, this study defines, derives, and validates the interrelationships among these parameters using the beam on elastic foundation (BOEF) model. Transit Cooperative Research Program (TCRP) Report No. 155 presents an inaccurate correlation between track modulus and tie spacing, stemming from the use of an unsuitable track foundation parameter. This misrepresentation may lead to erroneous interpretations in track design and performance analysis. This paper demonstrates that tie spacing has minimal or no effect on track modulus when the correct parameter is applied. A formula for the distribution factor proposed by the author in an earlier work is validated. A new expression for the distribution factor in terms of deflection is developed, validated, and linked to the track foundation parameter.