The effect of vibration on ballast beds

The Paper describes the effect of vibration on the stability of a bed of ballast, the material being crushed limestone in a nominal 19 mm single size grading. Stability is assessed by measuring the settlement of a plate placed on the surface when subjected to several cycles of sustained load. Tests on a vibrating table show that significant changes can be produced by vibration. An initially loose ballast bed is noticeably stabilized by vibration in which α> 1 (a being the ratio of peak table acceleration to that of gravity). A bed which has previously been well stabilized by many cycles of sustained load is modified by such vibration, into a structure which is indistinguishable from that resulting from vibration of an initially loose ballast bed. When vibration is applied at a loading platen placed on the surface of a bed previously stabilized by many cycles of sustained load, a resonant frequency is found, at which a small exciting force produces a fast continuous penetration of the platen into the surfa...