a. The sensitivity of the structure to total and/or
differential settlement as related to the structural
design. This is particularly true of structures to
be founded partly on fill and partly on natural
ground.
b. The ability of normal compaction equipment to
produce the desired densities in existing or locally
available materials within a reasonable range of
molding moisture content. If considered essential,
special equipment will be specified.
c. The compaction requirements for clean,
cohesionless, granular materials will be generally
higher than those for cohesive materials because
cohesionless materials readily consolidate when
subjected to vibration. For structures with
critical stability requirements and settlement
limitations, the minimum density requirements may be
altered. If only a cohesionless soil or only a
cohesive soil is used, the inapplicable values will
be deleted.
d. The exception to required high degree of
compaction in fills and backfills is in expansive
soils (see TM 5-818-7). Where it is necessary to
use materials having swelling characteristics,
usually CL or CH classifications, the specified
degree of compaction will be related to laboratory
test results for swelling under a considerable range
of molding moisture and compactive effort. In
swelling soils, it is important to specify a density
and molding moisture range that will enable the soil
to stay stable, striking a reasonable balance
between potential swell and excessive settlement
under load, even at the expense of accepting a
reduced bearing capacity. A maximum permissible
density should be established to minimize swelling.
If possible, soils with swelling characteristics
will be classified as unsatisfactory material,
particularly under critical stability structures.
e. ASTM D 1557 is satisfactory for establishing
moisture density characteristics of a material in
most cases. However, other modifications may be
necessary as discussed in this ASTM and under soil
tests in DM 21.3/ TM 5-825-2. The procedures and
precautions in the subgrade compaction paragraphs of
DM 21.3/TM 5-825-2, will be considered in
establishing minimum density requirements for a
particular project.
Modifications will be made to meet the backfill
requirements for deep-seated or subsurface
structures as discussed in TM 5-818-4.
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Backfill adjacent to any and all types of structures shall be placed and
compacted to at least 90 percent laboratory maximum density for cohesive
SECTION 02300
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