(1) Intercepting ditches and dikes are discussed in section II where track drainage is
discussed in detail.
(2) Plant roots hold the soil together, giving it additional stability. For civilian
railroads, introducing plant growth serves the further purpose of beautifying the right of way, a
consideration often underrated in importance in a competitive transportation market. A wide
variety of vegetation can be used: honeysuckle, shrubs, vines, roses, and various pasture sods.
Experience shows that vegetation on slopes pays for itself many times over by eliminating other
costly maintenance.
(3) Where space does not permit proper sloping or where slopes persist in sliding, the
usual remedy is to construct a retaining wall at the foot of the slope. The wall may be of
concrete, stone, timbers, or discarded crossties.
2.4.
BALLAST
Ballast is laid upon the subgrade, the prepared dirt surface of the roadbed. A good ballast
material should be workable, durable and strong enough to resist crushing, and angular in shape
to resist movement and to permit drainage when compacted. Ballast supports the crossties
resting upon it, holding them firmly in place. It thereby maintains alinement, provides uniform
support for the track, and, if properly structured, distributes traffic weight evenly on the roadbed.
Ballast provides a flexible base so that ties can be moved to adjust rails to proper alinement and
surface. It reduces dust and deters the growth of vegetation along the tracks. The following
three paragraphs discuss ballast materials, their selection, and the ballast section.
2.5.
BALLAST MATERIALS
Materials used for ballast and their application vary greatly. The right ballast material to
choose depends on the location and on the kind of traffic expected. High-speed, large-volume,
or heavy-tonnage traffic all justify an expensive ballast. The type of roadbed also influences
ballasting. A high fill of easily drained, stable soil does not require as much ballast as a cut
availability and cost. Brief discussions of the properties of the more common ballast materials
follow.
a. Broken or crushed stone, usually some form of lime-stone, ranges in size from 3/4 to
2 1/2 inches. This material is
22
Previous Page
