UFC 3-220-01N
15 AUGUST 2005
detailed plan for excavating and stockpiling the material. The plan should indicate the
location of stockpiles for various classes of backfill so that the material can be tested for
compliance with the specifications. The contractor may elect to obtain backfill material
from borrow or commercial sources rather than to separate and process excavated
materials. Then the specifications should require that stockpiles of the various classes
of needed backfill be established at the construction site in sufficient quantity and far
enough in advance of their use to allow for the necessary testing for approval unless
conditions are such that approval of the supplier's stockpile or borrow source can be
given.
8-6.3
Foundation Preparation. The provisions for preparation for structures
will generally not be grouped together in the specifications but will appear throughout
the earthwork section of the specifications under paragraphs on excavation, protection
of foundation materials, backfill construction, and concrete placement. When a structure
is to be founded on rock, the specifications will require that the rock be firm, unshattered
by blasting operations, and not deteriorated from exposure to the weather. The
contractor will be required to remove shattered or weathered rock and to fill the space
with concrete.
8-6.3.1
Structures on Soil. Specifications for structures founded on soil require
the removal of all loose material and all unsuitable material, such as organic clay or silt,
below the foundation grade. When doubt exists as to the suitability of the foundation
materials, a soils engineer should inspect the area and his recommendations should be
followed. When removal of rock material below the planned foundation level is required,
the over-excavation will usually require filling with concrete. The specifications also
require dewatering to the extent that no backfill or structural foundation is placed in the
wet.
Specifications for preparation of the soil foundation to receive backfill
require removing all debris and foreign matter, making the area generally level, and
scarifying, moistening, and compacting the foundation to a specified depth, generally
305 mm (12 in). Specific provisions may or may not be given with respect to leveling
procedures.
8-6.4
Backfill Operations. The specifications define the type or types of
material to be used for backfill construction and provide specific instructions as to where
these materials will be used in the backfill. The percentage of ASTM D 1557 maximum
dry density to be obtained, determined-by a designated standard laboratory compaction
procedure, will be specified for the various zones of backfill. The maximum loose-lift
thickness for placement will also be specified. Because of the shape of the compaction
curve, the degree of compaction specified can be achieved only within a certain range
of water contents for a particular compaction effort. Though not generally specified in
military construction, the range of water contents is an important factor affecting
compaction.
8-6.4.1
Compacting. The specifications sometimes stipulate the characteristics
and general type of compaction equipment to be used for each of the various types of
backfill. Sheepsfoot or rubber-tired rollers, rammer or impact compactors, or other
suitable equipment are specified for fine-grained, plastic materials. Non-cohesive, free
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