TM 5-818-4/AFM 88-5, Chap. 5
lowed for most sheepsfoot and pneumatic-tired rollers.
frost-susceptible materials or material containing ad-
Cohesive soils placed inapproximately lo-inch loose
ditives, such as calcium chloride, to lower the freezing
lifts will compact to approximately 6 inches, and cohe-
temperature of the soil water should be used. Each lift
sionless soils placed in approximately 8-inch base lifts
should be checked for frozen material after compac-
will compact to 6 inches. Adequate compaction can be
tion and before construction of the next lift is begun.
achieved in cohesionless materials of about 12- to 15-
If frozen material is found, it should be removed; it
inch loose-lift thickness if heavy vibratory equipment
should not be disked in place. Additives should not be
is used. The addition of vibration to rolling equipment
used indiscriminately since they will ordinarily change
used for compacting cohesive soils generally has little
compaction and water content requirements. Prior
effect on the lift thickness that can be compacted, al-
laboratory investigation should be conducted to deter-
though compaction to the desired density can some-
mine additive requirements and the effect on the com-
times be obtained by fewer coverages of the equip-
paction characteristics of the backfill material.
ment.
(b) Under no circumstances should frozen ma-
(b) In confined zones where clean cohesionless
terial, from stockpile or borrow pit, be placed in back-
backfill material is used, a loose-lift thickness of 4 to 6
fill that is to be compacted to a specified density.
inches and a vibratory plate or walk-behind, dual-drum
(c) Prior to halting construction during the
vibratory roller for compaction is recommended.
winter, the peripheral surface drainage system should
Where cohesive soils are used as backfill in confined
be checked and reworked where necessary to provide
zones, use of rammer compactors and a loose-lift thick-
positive drainage of surface water away from the exca-
ness of not more than 4 inches should be specified. Ex-
vation.
perience has shown that "two-by-four" wood rammers,
(d) Foundations beneath structures and backfill
or single air tampers (commonly referred to as
around structures should not be allowed to freeze, be-
"powder puffs" or "pogo sticks") do not produce suffi-
cause structural damage will invariably develop.
cient compaction.
Structures should be enclosed as much as possible and
(4) Density requirements. In open areas of backfill
heated if necessary. Construction should be scheduled
where structures will not be constructed, compaction
so as to minimize the amount of reinforcing steel pro-
can be less than that required in more critical zones.
truding from a partially completed structure since
Compaction to 90 percent of CE 55 maximum dry
steel will conduct freezing temperatures into the
density as obtained by MIL-STD-621 should be ade-
foundation.
quate in these areas. If structures are to be constructed
(e) Permanent backfill should be protected from
on or within the backfill, compaction of cohesionless
freezing as discussed in paragraphs 2-3h (3) and (4).
soils to within 95 to 100 percent of CE 55 maximum
Records should be made of all temporary coverings
dry density and of cohesive soils to at least 95 percent
that must be removed before backfilling operations are
of CE 55 should be required for the full depth of back-
resumed. A checklist should be maintained to ensure
fill beneath these structures. The specified degree of
that all temporary coverings are removed at the begin-
compaction should be commensurate with the
ning of the next construction season.
tolerable amount of settlement, and the compaction
(f) During freezing weather, records should be
equipment used should be commensurate with the al-
kept of the elevation of all critical structures to which
lowable lateral pressure on the structure. Drainage
there is the remotest possibility of damage or move-
blankets and filters having special gradation require-
ment due to frost heave and subsequent thaw. It is im-
ments should be compacted to within 95 to 100 per-
portant that frost-free bench marks be established to
cent of CE 55 maximum dry density. Table 5-1 gives a
which movement of any structure can be referenced.
summary of type of compaction equipment, number of
Bench marks also should be established on the struc-
coverages, and lift thickness for the specified degree of
tures at strategic locations prior to freezing weather.
compaction of various soil types (TM 5-818-1/AFM
(g) At the beginning of the following construc-
88-3, Chap. 7).
tion season and after the temporary insulating cover-
(5) Cold weather. In areas where freezing
ings are removed, the backfill should be checked for
temperatures either hamper or halt construction dur-
frozen material and ice lenses, and the density of the
ing the winter, certain precautions can and should be
compacted material should be checked carefully before
taken to prevent damage from frost penetration and
backfilling operations are resumed. If any backfill has
subsequent thaw. Some of these precautions are pre-
lost its specified density because of freezing, it should
sented below.
be removed.
(a) Placement of permanent backfill should be
(6) Zones having particular gradation require-
deferred until favorable weather conditions prevail.
ments. Zones that have particular gradation require-
However, if placement is an absolute necessity during
ments include those needed to conduct and control
freezing temperatures, either dry, cohesionless, non-
seepage, such as drainage blankets, filters, and zones
5-2
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