ANALYSIS OF STRESS DISTRIBUTION IN METER GAUGE RAILROAD TRACKS SUBJECTED TO MODERATE AXLE LOADS AND RAIL SPEEDS

Abstract

This paper presents the characteristics of traffic stress distribution in the track substructure with an emphasis on those of meter-gauge railroads subjected to moderate axle loads (12-20 metric tons) and rail speeds (50-120 km/h). Such conditions are prevalent to the contexts of rail transportation in Thailand. A computer program based on three-dimensional beam-on-elastic foundation (BOF) theory is employed to calculate stresses in the substructure due to traffic loads. An assemblage of rails, pads, and ties is supported by the substructure consisting of multiple layers of elastic materials. Each is characterized by a nonlinear model of stress-dependent resilient modulus. The numerical method is validated by the substructure stresses measured from a fully instrumented rail track section under real services. A series of numerical parametric studies are performed using the validated BOF model however with different boundary conditions. Key track parameters used in the calculations are the axle load, rail speed, and stiffness and thicknesses of the ballast, subballast, and subgrade layers. The values these parameters are selected to best represent the traffic and track conditions of railroads founded on the soft cohesive soils of the central region of Thailand. The calculated track stresses are analyzed and employed to determine cumulative deformations of the subgrade soil using a simple plastic strain model. Comparison between the predicted deformations due to repetitive axle loads and those monitored from the experiment track section is made. Then the applicability of this approach to predict subgrade settlements in meter-gauge tracks under moderate axle loads and rail speeds is preliminarily assessed.