Feature lines in the same site can only have one elevation at a crossing point. If two feature lines approach within a tolerance distance of 0.0001, the points collapse to a single point. If feature lines are so close that they nearly overlap, yet do not collapse, the topology model becomes much more difficult to represent. In these cases the model creates very small “sliver” enclosed areas, analogous to sliver triangles in a surface TIN model.
In most cases, sliver areas are not a problem, but excessive overlapping can be difficult to model in the topology and can extend the surface processing time. In particular, this can happen when you have multiple feature lines overlapping with slightly different geometry. Also, arcs tend to have more problems than lines when resolving overlapping geometry.
Keep these interactions in mind when creating feature lines for a grading plan. In general, if you try to represent duplicate feature lines, it is a good practice to put them in separate sites. Otherwise, visually inspect the feature lines within a site and remove any that are nearly tangent and not required. Remember these practices, and use them also when creating lot lines and alignments.