TM 5-818-1 / AFM 88-3, Chap. 7
Table 15-2. Compaction Density as a Percent of CE 55 Labortory Test Density
CE 55 Maximum Density, %
Cohesive
Cohesionless
Soils
Soils
Fill, embankment, and backfill
a
Under proposed structures, building
90
95
slabs, steps, and paved areas
Under sidewalks and grassed areas
85
90
Subgrade
Under building slabs, steps, and paved
90
95
areas, top 12 in.
Under sidewalks, top 6 in.
85
90
a
May be 85% relative density, whichever is higher.
ered ground. Methods of compaction controf during
especially attractive from an economic standpoint for
construction are described in TM 5-818-4/AFM 88-5,
development purposes. Dikes are usually required to
Chapter 5.
retain hydraulic fills on land and may be feasible for
underwater fills. Underwater dikes may be constructed
of large stones and gravel.
15-5. Fill settlements. A fill thickness of even 3 feet
a. Pervious fills. Hydraulically placed pervious
is a considerable soil load, which will increase stresses
fills with less than 10 percent fines will generally be at a
to a substantial depth (approximately 2B, where B =
relative density of 50 to 60 percent but locally may be
smallest lateral dimension of the fill). Stress increases
lower. Controlled placement is necessary to avoid silt
from the fill may be larger than those from structure
concentrations. Compaction can be used to produce
footings placed on the fill. Use procedures outlined in
relative densities sufficient for foundation support (table
chapter 10 to obtain expected settlements caused by fill
15-1). Existing uncompacted hydraulic fills of pervious
loading. Many fills are of variable thickness, especially
materials in seismic areas are subject to liquefaction,
where an area is landscaped via both cutting and filling
and densification will be required if important structures
to obtain a construction site. In similar cases, attention
are to be founded on such deposits. Rough estimates of
should be given to building locations with respect to
relative density may be obtained using standard
crossing cut and fill lines so that the proper type of-
penetration resistance. Undisturbed borings will be
building settlement can be designed (building may act as
required to obtain more precise evaluation of in situ
a cantilever, or one end tends to break off, or as a beam
density and to obtain undisturbed samples for cyclic
where the interior sags). Proper placing of reinforcing
triaxial testing, if required. For new fills, the coarsest
steel in the wall footings (top for cantilever action or
materials economically available should be used. Unless
bottom for simple beam action) may help control building
special provisions are made for removal of fines, borrow
cracks where settlement is inevitable; building joints can
containing more than 10 percent fines passing the No.
be provided at critical locations if necessary. The
200 sieve should be avoided, and even then controlled
combined effect of structure (one- and two-story
placement is necessary to avoid local silt concentrations.
residences) and fill loading for fills up to 10 feet in
b. Fine-grained.fills.
Hydraulically placed
thickness on sound soil and using compaction control
overconsolidated clays excavated by suction dredges
should not produce a differential settlement of either a
produce a fill of clay balls if fines in the washwater are
smooth curved hump or sag of 1 inch in 50 feet or a
permitted to run off. The slope of such fills will be
uniform slope of 2 inches in 50 feet.
extremely flat ranging from about 12 to 16H on 1V.
(1) These fills will undergo large
15-6. Hydraulic fills. Hydraulic fills are placed on
immediate con-
land or underwater by pumping material through a
pipeline from a dredge or by bottom dumping from
barges. Dredge materials vary from sands to silts and
fine-grained silty clays and clays.
Extensive
maintenance dredging in the United States has resulted
in disposal areas for dredge materials, which are
15-4
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