Application of Granular Material Pressure Cells to Measure Railroad Track Tie/Ballast Interfacial Pressures

This paper describes the development of a method to measure railroad track tie/ballast interfacial pressures using pressure cells specially designed for granular materials. Repeat measurements were taken during a several-month period on a Norfolk Southern Corporation high-tonnage mainline. The research employed new wood crossties routed so pressure cells could be recessed within the ties. Thus, the active surfaces of the pressure cells were flush with the tie bottoms. Cabling was run through a recess to the tie end. This greatly reduced the likelihood of damage to the instrumentation during track surfacing and lining activity. The ties were installed such that multiple cells were directly under consecutive rail seats of one rail. Several ties also had cells either at the center or the rail seat of the opposite rail. The researchers expended considerable effort to provide consistent ballast conditions for the instrumented ties and adjacent, undisturbed (transition) ties. Norfolk Southern crews surfaced and tamped through and on either side of the test section. This, plus consolidation through normal accruing train traffic, resulted in consistent measurements through the section. The paper presents ballast pressure magnitudes and distributions and discusses results, including the effects of variable ballast support, wheel loadings, and impact loadings. Typical vertical ballast pressure measurements directly under the rail seat, with compacted ballast and minimal impact forces ranged from 20 to 30 psi (140 to 210 kPa) under the heaviest common revenue wheel loadings.