Performance evaluation of polyurethane-stabilized railroad ballast under direct shear conditions

Abstract

The behavior of Elastan-stabilized and unstabilized ballast was explored using the large-scale direct shear apparatus under different normal stresses (σn) and shearing rates (Sr). Fresh granite ballast and Elastan polyurethane having a density of 1100 kg/m3 was used for the study. Further, a triangular aperture geogrid was also used to compare its benefits with that of Elastan treatment of ballast. Elastan-stabilized ballast samples were tested after a curing period of 3 days. Test results established that the shear strength of ballast was profoundly affected by both the applied normal stress and shearing rate. The friction (φ) and dilation (ψ) angles of unstabilized ballast were found to decrease from 65° to 59° and from 21° to 10°, respectively with an increase of σn and Sr. The results further confirmed that the Elastan treatment significantly enhanced the shear strength of ballast. The friction (φ) and dilation (ψ) angles of Elastan-stabilized ballast increases from 65° to 75° and 21° to 22°, respectively. The stabilization efficiency factor (Sef), defined as the fraction of the shear strength of stabilized ballast to that of unstabilized ballast, varies from 1.6 to 1.75 for Elastan-stabilized ballast. The breakage of ballast (Bg) increased from 7.62 to 11.72% with an increase of σn and Sr. Further, the geogrid reinforcement reduced the Bg from 11.72 to 4.24% when compared to unstabilized ballast. On the other hand, visual inspection of the Elastan-stabilized ballast indicated no degradation of ballast particles.