Feasibility of Impulse Response Test for Characterizing Railway Ballasts

Abstract

The contamination of ballast (a.k.a. ballast fouling) because of the intrusion of clay, rock dust, coal dust, or any other agent accelerates track degradation and affects the stability of the ballast in particular and the track in general. The feasibility of nondestructively characterizing the structural integrity of ballast using the dynamic stiffness measured with the impulse response (IR) method is explored in this paper. A number of large-size laboratory specimens were constructed at three different degrees of fouling using both rock dust and clay as fouling agents. Each specimen was tested at three moisture contents. Four different source-sensor configurations were examined. Characterizing the impact of ballast fouling with the IR method is feasible. Based on the practicality of field implementation and the detectability of fouling and moisture effects, the test configuration where the hammer energy is imparted to the tie and the receiver is placed on the ballast is the reliable one. The dry density and fouling percentage influence the IR stiffness more than the moisture content. The preloading force applied to the tie before IR testing also strongly influences the IR stiffness of clay-fouled and rock dust–fouled specimens.