Width. Provide a minimum of 18 inches from the toe of the ballast
to the edge of the finished grade. See AREA Manual, Chapter 1, Part 2,
Provide a minimum of 9 feet from track centerline to
the shoulder line.
Provide a minimum of 11 feet from track centerline
to the shoulder line.
Minimum Cut Dimensions. Consideration is to be given to drainage,
snow removal, debris removal, rock falls, and maintenance. See AREA Manual,
Chapter 1, Part 1.2, Design.
Slopes and Subgrade. Slope and subgrade criteria are as follows.
See AREA Manual, Chapter 1, Part 1, Roadbed.
Slope. Cut and fill slopes shall be designed according to a slope
stability analysis unless adequate local experience has shown a particular
slope to be stable.
Subgrade. For subgrade criteria, see AREA Manual, Chapter 1, Part
1, Section 1.2.5, Roadbed and NAVFAC DM-7.1 Soil Mechanics and DM-7.2
Foundations and Earth Structures. Subgrade cross slopes shall be 48
horizontal to 1 vertical. The subgrade shall slope in one direction beneath a
single track and shall be crowned between tracks for multiple tracks. In no
case shall the crown of the subgrade occur under the ties.
Geotextile Fabric. When the subgrade has a large amount of fines,
a geotextile fabric should be used between the subgrade and the ballast.
Geotextile fabrics should be man made and not biodegradable. Geotextile
fabrics should be designed to provide tensile reinforcements, filtration and
soil separation. Typical properties and standards specified should include:
ASTM D 1777
ASTM D 1682
ASTM D 1682
ASTM D 751
ASTM D 3786
Trapezoid Tear Strength
ASTM D 2261 or ASTM D 2262