Influence of Coal Fouling on the Shear Behavior of Elastan-Treated Railroad Ballast

Abstract

The shear behavior of coal-fouled unstabilized ballast and that stabilized with Elastan was assessed in direct shear mode at various normal stresses (σn) and shearing rates (Sr). The materials used in the test were fresh granite ballast and coal fines of mean particle sizes (D50) of 42 mm and 545 μm, triangular aperture geogrid, and Elastan polyurethane polymer with a density of 1,100 kg/m3. Test results indicated that the shear strength of both unstabilized and stabilized coal-fouled ballast is highly affected by the applied normal stress and shearing rate. The results further established the performance of ballast stabilized with Elastan to be significantly more enhanced than unstabilized ballast and that stabilized with geogrid. Furthermore, the results also confirmed that the shear strength of Elastan-stabilized ballast is highly influenced by the presence of coal fines. The friction angle (φ) of coal-fouled Elastan-stabilized ballast reduces from 75° to 65° and dilation angle (ψ) from 19° to 8° as the void contamination index (VCI) increases from 0% to 45%. The performance index of Elastan-stabilized ballast, expressed as the ratio of shear strength of fouled ballast to the shear strength of fresh and unstabilized ballast, lies in the range of 1.60–1.29. The breakage of fouled ballast (Bg) was found to decrease owing to the addition of coal fines. Further, analysis of tested samples revealed that while geogrid reduced the particle breakage considerably, the Elastan treatment completely eliminated the breakage of particles.