Quantcast SUBAQUEOUS PLACEMENT OF STONE OR SIMILAR MATERIALS

 
  
 
Construction of Stabilization Works
(f) Alternatives available to the construction forces if specifications call for a dike crown
width too narrow for the operation of construction equipment are to:
Construct "turn-arounds," or maneuvering areas, by widening the crown at
intervals along the dike. The expense of doing this will of course be
reflected, at least indirectly, in the bid price for the work if the work is
contracted out.
Construct the top portion of the dike (that portion which is higher than the
elevation at which there is a crown width sufficient for hauling and handling
stone) as a separate operation, in which stone that was previously
"stockpiled" alongside the dike, but outside the specified dike cross-section,
is pulled up and into the design cross-section. The piece of equipment which
performs this operation literally backs toward the end of the dike, finishing
the dike as it proceeds. Some inefficiency is involved in this method, and
some stone is inevitably left outside the design cross-section, especially if
some of the stockpiled stone is underwater.
(g) Stone dikes can be successfully constructed even if the entire structure riverward of the
bankline is underwater during construction, although careful control of the operation is
necessary. Precise control of the profile and crown width of the finished structure is not
feasible, but the structure will be functional nevertheless. An overrun in quantity is
likely, because of less precise placement and increased stone displacement by the flow
over the structure. This overrun will be offset in some cases by the relief provided by
flow over the structure that would otherwise have been diverted around the end of the
dike during construction, causing scour ahead of it, had it been above water during
construction.
10.4.3 SUBAQUEOUS PLACEMENT OF STONE OR SIMILAR MATERIALS
Conventional draglines and bucket machines of all descriptions can be used
successfully to place stone fill underwater. Bottom-dumping hopper barges can be used to
increase rate of placement. This practice is more common in European practice than in the
United States. Lacking such specialized equipment, ingenious use of available equipment,
such as coal hoppers mounted between pontoon barges, can expedite the work.
Subaqueous stone paving or granular filters can be placed more efficiently by
specifying the quantity in terms of weight or volume per unit of area covered rather than in
terms of blanket thickness. In-place thickness is difficult to measure underwater, and
adequate coverage can be obtained by careful placement of the material using a grid system
and pre-placement allocation of the amount of material to be placed per grid unit (for
example, 7 tons per 100 square feet, in lieu of a paving thickness of 15 inches). Regardless
of the placement and measurement procedure, the specified quantity should be greater than
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