Subgrade and Sub-ballast
The finished subgrade shall be covered with a sub-ballast composed of crushed rock or other suitable material
as approved by the Engineer. It shall be so placed that all high points in the tunnel floor are covered with a
minimum of 4 inches of sub-ballast. The sub-ballast shall be compacted and finished to true line, grade and
cross section suitable for ballasting and track laying. Filter fabric shall be placed between the sub-ballast and
subgrade, if required. Side ditches and subdrains shall be provided as required