15 AUGUST 2005
Settlements of Hydraulic Fills. If the coefficient of permeability of a
hydraulic fill is less than 0.0616 mm/minute (0.0002 ft/minute), the consolidation time for
the fill will be long and prediction of the behavior of the completed fill will be difficult. For
coarse-grained materials with a larger coefficient of permeability, fill consolidation and
strength buildup will be relatively rapid and reasonable strength estimates can be made.
Where fill and foundation soils are fine-grained with a low coefficient of permeability,
piezometers should be placed both in the fill and in the underlying soil to monitor pore
pressure dissipation. It may also be necessary to place settlement plates to monitor the
settlement. Depending on the thickness of the fill, settlement plates may be place both
on the underlying soil and within the fill to observe settlement rates and amounts.
Compaction of Hydraulic Fills. Dike-land hydraulic fills can be
compacted as they are placed by use of the following:
Driving track-type tractors back and forth across the saturated fill.
(Relative densities of 70 to 80 percent can be obtained in this manner for
Other methods such as vibratory rollers, vibro-flotation, terraprobing, and
compaction piles. Below water, hydraulic fills can be compacted by use of
terraprobing, compaction piles, and blasting.
Underwater Hydraulic Fills. For structural fill placed on a dredged
bottom, remove the fines dispersed in dredging by a final sweeping operation,
preferably with suction dredges, before placing the fill. To prevent extremely flat slopes
at the edge of a fill, avoid excessive turbulence during dumping of the fill material by
placing with clamshell or by shoving off the sides of deck barges. To obtain relatively
steep slopes in underwater fill, use mixed sand and gravel. With borrow containing
about equal amounts of sand and gravel, underwater slopes as steep as 1V on 2H may
be achieved by careful placement. Uncontrolled bottom dumping from barges through
great depths of water will spread the fill over a wide area. To confine such fill, provide
berms or dikes of the coarsest available material or stone on the fill perimeter.