TM 5-818-4/AFM 88-5, Chap. 5
areas where heavy equipment cannot operate. Rock-
tion equipment, such as vibratory plate or rammer
soil mixtures having greater than 8 to 10 percent bind-
type, will be specified before heavy equipment is al-
er should be prohibited in all areas. In the case of back-
lowed to operate over the structure. The specifications
fill containing rock, the density is not generally speci-
require that the surface of the backfill be sloped to
fied. Obtaining adequate density is usually achieved
drain at all times when necessary to prevent ponding
by specifying the compaction procedures. The specifi-
of water on the fill. The specifications also provide for
cations may require that these procedures be devel-
groundwater control, so that all compacted backfill
oped in field test sections.
will be constructed in the dry. Where select, free-
draining, cohesionless soils of high permeability are re-
b. Specifications may also require specific equip-
quired in areas where compaction is critical, the
ment and procedures to ensure adequate bedding for
specifications list gradation requirements. Gradation
round-bottom structures such as tunnels, culverts, con-
requirements are also specified for materials used for
duits, and tanks. Procedures normally specified for
drains and filters.
placement of bedding for these types of structures are
discussed in paragraph 5-1c (2).
d. Unusually severe specification requirements may
be necessary for backfill operations in confined areas.
The requirements may include strict backfill material-
placed against permanent concrete construction with
type limitation, placement procedures, and compac-
respect to the time after completion; this time period
tion equipment.
is usually from 7 to 14 days. To provide adequate pro-
tection of the structures during backfill construction,
e. It is not the policy of the Government to inform
the specifications require that the backfill be built up
the contractor of ways to accomplish the necessary
symmetrically on all sides and that the area of opera-
protection from freezing temperatures. However, to
tion of heavy equipment adjacent to a structure be lim-
ensure that adequate protection is provided, it may be
ited. Also, the minimum thickness of compacted mate-
necessary to specify that the contractor submit de-
rials to be placed over the structures by small compac-
tailed plans for approval for such protection.
6-3
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