The great majority of railroad roadbeds in service today were originally constructed many years ago and
without the benefit of modern methods and equipment, or the benefit of current engineering
understanding. In many instances the track was built directly on top of the native loose soils or on nearby
borrow soils that were loosely dumped and spread in place to form narrow shallow fills with steep side
slopes. Little attention, if any, was given to selecting soils with more favorable roadbed properties or
compacting the roadbed soils before constructing track. However, over the years, these roadbeds have
tended to become firm and stable from the compaction and consolidation effects of rail traffic and from the
numerous surfacing cycles that have contributed granular materials and ballast to the roadbed. Subsurface
exploration of existing roadbeds will often reveal several layers of soil, imported granular materials, and old
ballast of varying thicknesses and depths. An example of a distorted roadbed and method of reporting such
conditions is shown in Figure 1-1-12.