A deep investigation into the mechanisms and factors producing mud pumping of railway track

Abstract

Ballast degradation and mud pumping are common issues facing all railroads in which slurry within the ballast pumps up around the surface of the track during train operations. This often corresponds to poor drainage, loss in track geometry, reduced ballast strength and stiffness, and, in the worst cases, can lead to derailment. Despite the prevalence of this problem, the mechanisms behind mud pumping and the factors influencing it have not been fully investigated, although past studies have determined that fines and water in the ballast, as well as repeated dynamic wheel loads, need to act together to produce mud pumping. Researchers at MxV Rail (formerly TTCI) have further investigated mud pumping situations from both the test track at the Facility for Accelerated Service Testing (FAST) and multiple revenue service track locations to further understand the underlying mechanisms of ballast mud pumping. These investigations have shown that some (and possibly most) ballast mud pumping situations are surficial problems, originating from the wet regions just around the ties (sleepers), which is the focus of this paper. However, other mud pumping situations include seasonal or perched water table below the bottom of the ties that causes moisture and fines to pump up to the surface from the underlying subgrade or lower degraded ballast and subballast layers.