Development of inter-particle friction in a railway ballast

A detailed experimental programme investigated how the coefficient of friction at particle contacts for a typical UK railway ballast varied during cyclic loading. Despite a decrease of roughness, the friction coefficient increased steadily, stabilising in the region of tens of cycles. In contrast to previous work on the contact behaviour of sands, water inundation caused a significant but reversible decrease of the coefficient, while the generation of a significant amount of abraded fines did not affect it, nor did the load level.