Characterization of Ballast Particle Movement at Mud Spot

Abstract

Mud pumping has been known to cause severe track degradation and compromise the safety of train operations. Mud pumping is normally the result of simultaneous upward intrusion of fine-grained soils into the ballast voids and downward penetration of ballast particles into the subgrade. Understanding ballast particle movement in clean versus muddy track and under dry versus wet conditions is critical for railroad engineers to make timely and effective maintenance decisions. SmartRock, a battery-powered wireless device that is produced using 3D printing technology and resembles a piece of ballast, can sense, record, and transmit its movement in real time. SmartRocks were recently used in a field test to investigate ballast particle movement in two sections of Norfolk Southern track: a control section with clean ballast and a section with an established mud-pumping problem. SmartRocks were installed in the ballast cribs in each section to investigate particle movement under both freight and passenger trains. The results show the differences of tie and ballast particle movement in clean and mud-spot sections under different freight trains. Tie acceleration was decaying from the previous wheel load under the middle of car in the mud-spot section; ballast particle acceleration appeared to be identical in both sections when the ballast condition was dry but severer in the mud-spot section when the ballast condition was wet. Two characteristics of ballast movement were used to assess ballast condition: peak acceleration range and Arias intensity. These results can be used to identify potential problematic locations on the track to prevent major repair in the future.