Multi-objective optimisation methodology for stiffness combination design of bridge-embankment transition zones in high-speed railways

Bridge-embankment transition zones, in which unexpected amplifications of vehicle-track interactions and infrastructure degradation are concentrated, are critical areas of high-speed railways. To mitigate the dynamic issues induced by uncertain filler stiffness, an available stiffness combination of transition zone components is required. Combining with robust designs, a multi-objective optimisation methodology is proposed to determine the compromise design of transition zones, which considers trade-offs among dynamic stress, dynamic displacement and system robustness. An optimal stiffness combination of subgrade bed surface layer (E1) and graded broken stone area (E2) in a typical bridge-embankment transition zone is presented by employing this methodology. The results indicate that the Pareto fronts visually show the dynamic response contradiction. Based on the conflicting evaluation criteria, i.e., minimizing the displacement and stress of the subgrade and maxi-mizing the system robustness, the knee points objectively render the best compromise design with E1 and E2 values of 1200 and 1000 MPa, respectively. Not only the dynamic response of the vehicle-track-subgrade system but also the negative effect brought by filler uncertainties are well controlled. Such a methodology is available for configuration design of projects in which uncertainties exist and design criteria are hard to weigh.