TM 5-818-4/AFM 88-5, Chap. 5
ing and another place the backfill. It is probable that
a. Specifications for structures founded on soil re-
the excavation contractor will have little or no interest
quire the removal of all loose material and all unsuit-
in stockpiling the excavated materials in a manner
able material, such as organic clay or silt, below the
conducive to good backfilling procedures. When such a
foundation grade. When doubt exists as to the suitabil-
situation can be foreseen, the specifications should set
ity of the foundation materials, a soils engineer should
forth stockpiling procedures. The justification for such
inspect the area and his recommendations should be
requirements would be economy and optimum use of
followed. When removal of rock material below the
materials available from required excavation as back-
planned foundation level is required, the overexcava-
fill.
tion will usually require filling with concrete. The
(2) The specifications will contain provisions for
specifications also require dewatering to the extent
removing, segregating, and stockpiling or disposing of
that no backfill or structural foundation is placed in
material from the excavation and will refer to the
the wet.
plans for locations of the stockpiles. The subsoil condi-
b. Specifications for preparation of the soil founda-
tions and engineering characteristics requirements
tion to receive backfill require removing all debris and
may state that the specifications must be quite defi-
foreign matter, making the area generally level, and
nite concerning segregation and stockpiling proce-
scarifying, moistening, and compacting the founda-
dures so that the excavated materials can be used most
tion to a specified depth, generally 12 inches. Specific
advantageously in the backfill. The specification may
provisions may or may not be given with respect to lev-
require that water be added to the material or the ma-
eling procedures.
terial be aerated as it is stockpiled to approximate opti-
mum water content, that the stockpile be shaped to
6-4. Backfill operations. The specifications de-
drain and be sealed from accumulation of excess wa-
fine the type or types of material to be used for backfill
ter, and that the end dumping of material on the stock-
construction and provide specific instructions as to
pile be prohibited to prevent segregation of material
where these materials will be used in the backfill, The
size or type along the length of the stockpile.
percentage of CE 55 maximum dry density to be ob-
(3) An alternative to this latter action would be to
tained, determined by a designated standard labora-
specify the various classes of backfill required and
tory compaction procedure, will be specified for the
leave the procedure for stockpiling the materials by
various zones of backfill. The maximum loose-lift
type to the discretion of the contractor. In this case,
thickness for placement will also be specified. Because
the contractor should be required to submit a detailed
of the shape of the compaction curve (see discussion of
plan for excavating and stockpiling the material. The
compaction characteristics in Section B-1, app. B), the
plan should indicate the location of stockpiles for vari-
degree of compaction specified can be achieved only
ous classes of backfill so that the material can be
within a certain range of water contents for a particu-
tested for compliance with the specifications. The con-
lar compaction effort. Though not generally specified
tractor may elect to obtain backfill material from bor-
in military construction, the range of water contents is
row or commercial sources rather than to separate and
an important factor affecting compaction.
process excavated materials. Then the specifications
a. The specifications sometimes stipulate the char-
should require that stockpiles of the various classes of
acteristics and general type of compaction equipment
needed backfill be established at the construction site
to be used for each of the various types of backfill.
in sufficient quantity and far enough in advance of
Sheepsfoot or rubber-tired rollers, rammer or impact
their use to allow for the necessary testing for approv-
compactors, or other suitable equipment are specified
al unless conditions are such that approval of the sup-
for fine-grained, plastic materials. Noncohesive, free-
plier's stockpile or borrow source can be given.
draining materials are specified to be compacted by
6-3. Foundation preparation. The provisions
saturating the material and operating crawler-type
for preparation for structures will generally not be
tractor, surface or internal vibrators, vibratory com-
grouped together in the specifications but will appear
pactors, or other similar suitable equipment. The
throughout the earthwork section of the specifications
specifications generally will prohibit the use of rock or
under paragraphs on excavation, protection of founda-
rock-soil mixtures as backfill in this type of construc-
tion materials, backfill construction, and concrete
tion. However, when the use of backfill containing
placement. When a structure is to be founded on rock,
rock is permitted, the maximum size of the rock is giv-
the specifications will require that the rock be firm,
en in the specifications along with maximum lift thick-
unshattered by blasting operations, and not de-
ness, loading, hauling, dumping, and spreading proce-
teriorated from exposure to the weather. The contrac-
dures, type of compaction equipment, and method of
tor will be required to remove shattered or weathered
equipment operation. The specifications should pro-
rock and to fill the space with concrete.
hibit the use of rock or rock-soil mixtures as backfill in
6-2
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