Frost heave is a well-known phenomenon in cold regions. It may happen in the wet clayey ground during winter in seasonally frozen regions and during autumn to winter in active layers in permafrost regions. The railway track upheaval, which happens in cold regions, is generally understood as due to frost heaving in subgrade layers. However, it has been confirmed that the upheaval due to frost heaving sometimes happens in the ballast layers. This understanding has been acquired by observing active railway tracks in northern Japan. Samples have been collected from ballast and subgrade layers and have been examined their frost heave susceptibilities along with mineral compositions with X-ray diffraction analysis. The results confirmed that fine materials in the ballast layers consist of clayey minerals and crushed rock-forming minerals of ballast. Those fine minerals have confirmed to be frost heave susceptible with frost heave tests. A series of frost heave tests has conducted using crushed rock and fine material, i.e. Kaolinite, mixture and confirmed that the mixtures frost heave. The frost heave susceptibility of the mixture is almost proportional to the saturation ratio of the fine materials in its voids, even if the voids of the crushed rock are not saturated with fine materials. This has been understood that initially crushed rocks support the overburden and the fine materials in voids does not have to support overburden. Then the high heave ratio is expected in the fine materials until the voids are filled with fine materials and ice lenses. After the voids are filled with the fine materials and ice lenses, segregating ice lens starts to push up the overburden, 1 .e. ballast layer, and cause macroscopic upheaval due to frost heaving.
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