Shear Strength and Drainage Characteristics of Elastomeric Polyurethane Treated Coal-Fouled Ballast

Abstract

The shear behavior and drainage characteristics of coal-fouled ballast when treated with elastomeric polyurethane are assessed by means of large-scale direct shear and permeability tests. The results from direct shear tests confirmed that the shear strength of both stabilized and unstabilized coal-fouled ballast was highly influenced by the extent of fouling (VCI: void contamination index). The performance index (PI) of elastomer-stabilized coal-fouled ballast (ESFB), determined as the fraction of shear strength of fouled ballast to the shear strength of fresh and unstabilized ballast, lies in the range of 1.23 to 0.84. Moreover, the performance of ESFB having VCI ≥30% was found to be either similar to or poorer than that of clean ballast without any treatment, thus indicating that the elastomer treatment may be provided only to ballast with VCI ≤30%. The results from constant head permeability tests indicate that the hydraulic conductivity of ballast ( k) is highly influenced by the presence of fouling materials but is only slightly reduced as a result of the elastomer stabilization. The k of ballast decreased from 43 to 0.18 mm/s as the VCI increased from 0 to 75%. For VCI ≥ 45% the k of ballast was found to be lower than that recommended for sub-ballast. On the other hand, the k of ballast reduced slightly from 43 to 37 mm/s because of the elastomer stabilization. Furthermore, an empirical relationship is established between k and e to determine the k of both stabilized and unstabilized fouled ballast.

Behaviour of coal-fouled elastomeric polyurethane-stabilized ballast under cyclic loading

“…However, the geogrid and elastomer reinforced samples have slightly higher voids than that of USB. The values of e f computed here are used to predict the hydraulic conductivity of ballast ( k ) using the empirical equation reported by Hussaini and Gundavaram 36 (equation (6)). The final hydraulic conductivity of ballast ( k ) predicted using equation (6) and the hydraulic conductivity of ballast ( k ) before the cyclic loading as reported by Hussaini and Gundavaram 36 are plotted in Figure 6(b).

Figure 6.Change in (a) void ratio and (b) hydraulic conductivity of ballast with void contamination index (VCI).

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“…The values of e f computed here are used to predict the hydraulic conductivity of ballast (k) using the empirical equation reported by Hussaini and Gundavaram 36 (equation ( 6)). The final hydraulic conductivity of ballast (k) predicted using equation ( 6) and the hydraulic conductivity of ballast (k) before the cyclic loading as reported by Hussaini and Gundavaram 36 are plotted in Figure 6(b).…”

“…33 On the other hand, the limited available studies on coal fouled polyurethane-stabilized ballast indicate that the effect of fouling content on the performance of polyurethane-stabilized ballast was found to be minimal. [34][35][36] Dӧlçek 34 stated that the polyurethane foam is effective in reducing the vertical plastic strains of ballast that is heavily fouled with clay and sand under cyclic loading conditions. Similarly, Gundavaram and Hussaini 35 reported that the effect of coal fouling content on the reduction of shear strength of polyurethane-stabilized ballast is minimal under direct shear loading.…”