observing fall of small rocks of high density and approximately spherical 
shape. Second, to achieve a dilute suspension and rapid volume movement 
useful velocities will usually be considerably higher than the minimum for 
particle suspension. The net flow velocity upward would, of course, be the 
difference between the fluid velocity and the falling velocity of the particle. 
The practices in wood particle handling are fairly well standardized. A typ- 
ical practice is to specify a minimum velocity in a vertical riser and a minimum 
velocity in a horizontal run. For wood waste the velocity is held between 
2,500 and 5,000 feet per minute, with the lower value useful for sawdust and 
the higher value for heavy chips (Marks, 1958). Similar data are not readily 
available for water-filled conveyors, but Marks does give a few hints on the 
design of ash-conveying systems and slurry pipelines for coal. 
Tunnel excavators have considered fluid handling of the spoil (muck) 
as it comes from the working face of a tunnel boring tool. The requirements 
for rapid excavation with the type of cutters commonly used are incompatible 
with use of a slurry system. The trend is to develop cutter systems that will 
produce the maximum size fragments possible, as this generally requires the 
least power per unit weight of spoil. To successfully move this material long 
distances through a pipeline requires either (1) finely subdividing the frag- 
ments in a crusher to allow use of relatively low velocities or (2) using very 
high velocities to transport a dilute slurry of the large fragments. Unfortunately, 
either approach requires many times as much power as the boring machine, the 
first for crushing, the second for pumping. Nevertheless, this appears to be the 
only reasonable approach to high production material handling over along 
distance which can keep up with advances in the output of tunneling machines 
(National Research Council, 1968). 
Fortunately, the probable material handling rates foreseen for the 
deep-ocean application are much less than those in surface dredging. Since 
it will usually be practicable to move the spoil only a short distance, power 
requirements will be moderate. In developing cutter heads for various kinds 
of spoils (from oozes to soft rock), fine subdivision to facilitate handling as 
a slurry in seawater should be kept as a goal. A similar goal should be set for 
developing rock disintegrating techniques as discussed in this report under 
“Large Hole Penetration of Competent Rock.” 
To summarize, slurry-handling systems suitable for spoil removal are 
in rather broad use industrially, but there is a paucity of technical literature, 
either empirical or theoretical, on which to base new designs. This is probably 
because, in dredging operations especially, simple rules of thumb, such as 
inducting 10 times as much water as spoil, seem to work well. To develop 
a spoil-milling concept as proposed in this report, some practical experience 
on avariety of materials should be accumulated in controlled tests of early 
designs. 
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