Abstract
'Hanging sleepers', which have gaps between sleepers and ballast layer are often found in the neighborhood of rail joints or rugged surface rails. This suggests that differential settlement of the ballast layer is due to impact loading generated by the contact between running wheel and rugged surface rail. Then cyclic loading tests were performed on crushed-stone layer with two loading patterns, the one is a cyclic impact loading and the other one is cyclic 'standard' loading controlled at 1/10 loading velocity of the impact loading. It was shown that the crashed-stone layer deforms with volumetric expansion during every off-loading processes under the cyclic impact loading. This phenomena prevents crushed stone layer from forming stable grain columns, then the residual settlement under the cyclic impact loading is larger than that under the cyclic 'standard' loading. A simple mass-spring model simulates that two masses move in the opposite direction with increased frequency of harmonic excitation.
