Bottom excavation and drilling of soft rocks and most soils can 
probably best be accomplished with a numerically controlled, independently 
operating machine with controls similar to those used by a milling machine 
in metal. The spoil material can best be removed from the work site as a 
slurry in seawater. 
Early future work on this or an alternative concept will probably be 
concentrated on the positioning and control aspects, both in analysis and in 
demonstration hardware. 
SPOIL REMOVAL 
In a typical dry-land excavation or drilling operation, a major part 
of the equipment, effort, and cost is related to horizontal translatory handling 
of the loosened material. Exceptions are found on large construction sites 
where permanent high-volume conveyors can be amortized during a project 
as, for instance, handling crushed rock in building a dam or on large dredging 
operations where sand, soil, and rocks are transported either by conveyor 
buckets or in a pipe as aslurry. Carrying the loosened material or spoil as 
a suspension in a moving fluid would be economical more often than gener- 
ally appreciated (Beck, 1968), and the trend to this approach can be seen by 
the increased activity in development of dredges, semiportable pneumatic 
systems, and particularly concrete pumps. 
The basic problem in handling a broad spectrum of fragmented spoil 
lies in the cohesiveness of damp soils, high density and variability in rock 
sizes, and in the low density and viscosity of air the only fluid always avail- 
able and conveniently usable in most systems. The use of water may frequently 
be worth considering where it is available, provided the solid medium is amen- 
able to ready separation in simple equipment and provided a body of water 
can be held at the excavation point. For harbors, mining dredging, and 
probably many large pit excavations where water is either present in the 
soil because of a high water table or can conveniently be introduced without 
endangering the stability of the finished walls, it appears to be a logical medium 
for rapid and economical movement. Water should become increasingly attrac- 
tive as a medium for spoil removal when the types of automated equipment 
and control outlined in previous sections of this report are developed. Where 
a friable, relatively dry material is being excavated, similar advantages should 
be readily achievable with air as the moving material. However, for reasons 
obvious from the following discussion, air velocities will have to be quite 
high except for any but very finely divided material (see Figure 53). This 
is not to indicate that the power expenditure necessary to achieve these high 
65 
