Effect of Coal Fouling on Railroad Ballast Under Direct Shear Loading Conditions

Abstract

Abstract Contamination of ballast generally occurs due to particle breakage, infiltration of other undesired materials from the surface or base of the ballast is one of the primary reason for track deterioration. In this context, large scale direct shear tests were conducted to examine the shear behavior of unstabilized and geogrid-stabilized fresh and coal fouled ballast. Fresh granite ballast with an average particle size (D50) of 42 mm and triaxial geogrid having 69 × 69 mm aperture were used in this study. Tests were conducted at different Void Contamination Index (VCI) values ranging from 0 to 60% at a constant shearing rate (Sr) of 3 mm/min and normal stress (σn) of 90 kPa. The test results revealed that the shear strength of ballast is highly influenced by the coal fouling. The friction (φ) and dilation angles (ψ) of unstabilized ballast is found to decrease from 63.06° to 55.55° and 17.7° to 11.22°, respectively as the VCI increases from 0 to 60%. It is further observed that the breakage of ballast (Bg, computed in terms of Marsal’s breakage) decreases from 9.37 to 3.98% with the presence of coal fines. However, the presence of geogrid was found to increase the friction angle and reduce the particle breakage and dilation of fresh and coal fouled ballast. These test results show the effectiveness of triaxial geogrid in stabilizing the fresh and coal fouled ballast.