PERFORMANCE OF LARGE-SCALE MODEL SINGLE TIE-BALLAST SYSTEMS.

Large-scale models of a single tie-ballast system were constructed over artificial ballast support that had variable compressibility. The principal objectives of the experimental work were to investigate the influence of load level and ballast support compressibility on the rate of accumulation of permanent deformations and ballast degradation. The test results show that at a given load level the rate of tie settlement is quite sensitive to ballast support compressibility. A competent ballast support resulted in a deformation-log tonnage response that was essentially linear. However, progressively weaker supports gave increasing semilogarithmic rates of settlement with tonnage. For a given support compressibility, a critical load level was identified that, if exceeded, led to a dramatic increase in settlement rate.