ABSTRACT
One of the main functions of railroad ballast is to resist the forces applied to the sleepers and to perform as the railroad super-structure foundation. Fouling (sand and fine size granular material) that infiltrates the pore space negatively impacts the shear strength and deformation properties of the ballast. Increase in amount of fouling and its inseparable associated moisture, results in a gradual deterioration of the track to the point of needing maintenance. Also this can lead to a decrease in track class and a reduction allowable train speed. In this study fouled ballast samples provided by the Transportation Technology Center Incorporated (TCCI) from Metro-North Railroad site were used to evaluate the effects of water content on the bearing capacity of fouled ballast. Large scale triaxial tests with 10-inch (25.4 cm) diameter were conducted to determine the drained strength parameters of the ballast and evaluate the bearing capacity under different water content conditions. The tests were performed at water contents varying from 0% to the field capacity and confining pressures varying from 5 to 25 psi (34.5 to 172 kPa). In addition, the 10-inch (25.4 cm) diameter test parameters were compared with 6-inch (15.2 cm) diameter on the same samples to assess the triaxial size effects on the strength properties. This research has shown that size effects of ballast testing has little effect on determination of bearing capacity.
