In geomechanics and engineering practice one of the many uses of man-made and natural coarse-sized and uniformly graded granular materials is to distribute and transfer loads from a surface structure or system to the subgrade as uniformly as possible. A typical example is railroad ballast, which is a highly coarse gravel, comprised of particles with sizes in the range of 30 to 70 mm, which is used to fill in irregular surface topology and provide embankment support for railroads. While ballast is typically deposited or placed at variable packing densities, it is expected to behave elastically and exhibit minimal stiffness and strength degradation over long time periods, and after large numbers of repeated load cycles. For moderate stress levels, there is experimental evidence that indicated elastic shake-down at a densified state after repeated roll-over load cycles. After numerous cycles the response is characterized by the resilient elastic modulus. However, for large stress levels and due to complex three-dimensional features in the rail-tie/sleeper-ballast system the material continues to degrade until plastic shake-down is reached. Since the performance of modern high-speed trains rely heavily on the dynamic interaction behavior of the vehicle-support system, it is of great practical importance to determine the overall characteristics and constitutive properties of the ballast. The presentation will describe experimental results and analytical modeling issues related to cyclic shake-down of ballast.
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