Performance of Fouled Railroad Superstructure Subjected to Traversing Heavy Haul Trains
Abstract
Railway transportation offers capacity, efficiency, and safety to serve the needs of modern societies for moving freight and people. Therefore, the sustainability and safety of railroad infrastructure are of paramount importance for securing transportation needs. Freight train passby loads increase the surface deformation of railroad substructure due to cumulative plastic strains, which lead to surface deviation of the railroad tracks. Correspondingly, railroad maintenance is necessary to sustain track geometry alignment and to prevent deterioration of the sub-structure over time, which can increase operating costs significantly. Therefore, this thesis evaluates the performance of fouled railroad superstructure through laboratory testing of fouled sub-structure material, field monitoring of fouled track section at the test site and finite element analysis of the fouled track performance. First, isotropically consolidated drained cyclic triaxial tests were conducted on fouled sub-ballast retrieved from the test site. Test results were used to assess the material shear stiffness during the loading cycles. Operational speed limits were deduced from the stress-strain behavior of the fouled sub-ballast to prolong the service life of the fouled foundation bed. Next, railroad superstructure performance due to track fouling was assessed through a field monitoring program. The normalized maximum rail-tie tensile force was employed to analyze the uplift resistance of a CWR section at the cross-tie. Results indicate that the tie-load ratio may misrepresent the superstructure efficiency in fouled ballast beds. Alternatively, the range of influence of wheels along with the uplift ratio may be used to assess fouled railroad performance using the proposed empirical models. Measured accelerations during the passage of various trains were analyzed in time and frequency domains. Train velocity guidelines are provided to minimize train-induced vibrations in the fouled tracks. Finally, a validated dynamic two-dimensional finite element model was developed to investigate the effect of train velocity on the generated positive and negative excess pore water pressures using loading time histories considering different train velocities. Results demonstrate that positive excess porewater pressure developed in the sub-structure due to cyclic loading. Undrained conditions prevailed in the sub-grade and sub-ballast. Capillary fringes were noticed to form in the sub-ballast layer.