Determination of Unit Ballast Resistance from Discreet Resistance per Tie

This is demonstrated in an earlier paper that the current practice to determine the unit resistance of ballast, τ [N/cm] from resistance per tie, RPT [N] by dividing it with tie spacing is not appropriate. Ballast resistance depends on the quality of track support, which mainly depends on tamping with subsequent stabilization of track and ballast quality. The quality of track support is characterized by the characteristic length of a track. The higher the quality of track support, the shorter the characteristic length or vice versa. Thus, unit ballast resistance is inversely proportional to the characteristic length of a track. The constant of proportionality is assumed to be equal to the RPT; this leads to a relation between unit resistance of ballast and the characteristic length of a track. Using the relationship, unit ballast resistances are computed and validated by comparing with unit ballast resistance values suggested by code or used by railways. The track stiffness can be determined quickly by a simple test at site as opposed to the characteristic length. The characteristic length is related with the track stiffness. Thus, τ-value is also related with the track stiffness. Using the relationship, unit ballast resistances are also computed and validated. From Prud’homme law resistance values for concrete and wood tie in a stabilized track is related by a factor of 1.5. Based on literature and analysis done in the paper, a conservative qualification of RPT (discreet resistance of tie) and τ (unit resistance of ballast) is presented. Track professional may use the τ-values presented in the paper to estimate breathing length, rail break gap, and track buckling load. The paper would help track professionals to choose their own values too.