TM 5-818-1 / AFM 88-3, Chap. 7
solidation for about the first 6 months until the clay balls
pore pressure dissipation. It may also be necessary to
distort to close void spaces. Additional settlements for a
place settlement plates to monitor the settlement.
1-year period after this time will total about 3 to 5 percent
Depending on the thickness of the fill, settlement plates
of the fill height.
may be placed both on the underlying soil and within the
(2) Maintenance
dredgings
and
fill to observe settlement rates and amounts.
d. Compaction of hydraulic fills. Dike-land
hydraulically placed normally consolidated clays will
initially be at water contents between 4 and 5 times the
hydraulic fills can be compacted as they are placed by
liquid limit. Depending on measures taken to induce
use of-
surface drainage, it will take approximately 2 years
(1) Driving track-type tractors back and
before a crust is formed sufficient to support light
forth across the saturated fill. (Relative densities of 70 to
equipment and the water content of the underlying
80 percent can be obtained in this manner for
materials approaches the liquid limit. Placing 1 to 3 feet
cohesionless materials.)
of additional conhesionless borrow can be used to
(2) Other methods such as vibratory
improve these areas rapidly so that they can support
rollers, vibroflotation, terraprobing, and compaction piles
surcharge fills, with or without vertical sand drains to
(chap 16). Below water, hydraulic fills can be compacted
accelerate consolidation. After consolidation, substantial
by use of terraprobing, compaction piles, and blasting.
e. Underwater hydraulic fills. For structural fill
one- or two-story buildings and spread foundations can
be used without objectionable settlement. Considerable
placed on a dredged bottom, remove the fines dispersed
care must be used in applying the surcharge so that the
in dredging by a final sweeping operation, preferably with
shear strength of the soil is not exceeded (i.e., use light
suction dredges, before placing the fill. To prevent
equipment).
extremely flat slopes at the edge of a fill, avoid excessive
c. Settlements of hydraulic fills.
If the
turbulence during dumping of the fill material by placing
coefficient of permeability of a hydraulic fill is less than
with clamshell or by shoving off the sides of deck barges.
0.0002 foot per minute, the consolidation time for the fill
To obtain relatively steep slopes in underwater fill, use
will be long and prediction of the behavior of the
mixed sand and gravel. With borrow containing about
completed fill will be difficult.
For coarse-grained
equal amounts of sand and gravel, underwater slopes as
materials with a larger coefficient of permeability, fill
steep as 1V on 2H may be achieved by careful
consolidation and strength buildup will be relatively rapid
placement. Uncontrolled bottom dumping from barges
and reasonable strength estimates can be made. Where
through great depths of water will spread the fill over a
fill and foundation soils are fine-grained with a low
wide area. To confine such fill, provide berms or dikes of
coefficient of permeability, piezometers should be placed
the coarsest available material or stone on the fill
both in the fill and in the underlying soil to monitor
perimeter.
15-5
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