A Deep Investigation into the Mechanisms and Factors Producing Mud Pumping

Abstract

Mud pumping is a common issue facing all railroads in which wet fines within the ballast pump up around the ties and onto the surface of the track during train loading. This often corresponds to poor drainage, loss in track geometry, reduced ballast strength and stiffness, and in the worst case leading to ballast failure. Despite the prevalence of this problem, the mechanisms behind mud pumping and the factors influencing it are not fully understood, although past investigations have determined that fines and water in ballast, as well as repeated dynamic wheel loads, need to act together to produce mud pumping. An improved understanding is to how it will allow for better prediction of mud pumping and the negative effects associated with it, along with improved maintenance planning and techniques. Transportation Technology Center, Inc. (TTCI) has further reviewed and investigated mud pumping situations from both its “rainy section” test zone at the Facility for Accelerated Service Testing (FAST) near Pueblo, Colorado, and multiple revenue service locations in attempt to understand the underlying mechanisms behind mud pumping. The rainy section at FAST and some revenue service sites suggested that some (and possibly most) mud pumping situations are purely surficial, originating from the wet regions just around the ties. However, other mud pumping situations have shown a seasonal or perched water table below the bottom of the ties that appears to cause moisture and fines to pump up to the surface from the subgrade or lower ballast layer. TTCI plans to continue to investigate different mud pumping situations with the end goals of developing ballast maintenance guidelines and improving track substructure-induced track geometry degradation forecasting models.