Useful locations for subbottom installations of the types discussed 
in the next section might not be where the rock is exposed. Typically, it 
might be necessary to penetrate a significant layer of silt, clay, or ooze. To 
drill into the rock with a large drilling machine, it will be necessary to sink 
a large-diameter casing to rock, make a minor penetration and grout or 
otherwise set the lower end of the casing in the rock. The enclosed sedi- 
ment could then be rather readily removed by pumping or jetting, or a 
combination, depending upon the consistency. In any case, the sediment 
removal appears to be the only part of the operation which can be done 
with certainty by existing, proved techniques. 
The anchored casing would be useful for subsequent operations, as 
it could form a guide for the large-diameter boring machine of the type shown 
schematically in Figure 56. This would solve a difficult problem of vertical 
stability and obtaining initial entry with the large machine, which must be 
guided until it makes penetration. 
The presence of this large tube will not simplity entry to the 
underground workspace, however, because it must remain as part of the 
completed installation. But, if techniques for securing a positive seal at its 
lower end can be developed, it would be comparatively simple to make the 
final closure at the top of the tube (point A, Figure 57). This could readily 
be entered through a suitable hatch system from either a small submersible 
Or a personnel transfer capsule (PTC). It would be possible in principle to 
enter from a suitable personnel transfer capsule if the pressure closure were 
made at the bottom of the tube, but this method does not appear attractive 
from a safety and utility standpoint under present concepts for control. Con- 
siderable study will be required before such an operation can be conducted 
with confidence. The presence of the tube would also complicate the process 
of subbottom excavation and spoil removal. These problems would be miti- 
gated by drilling a very deep hole which could be used for storage of spoil from 
the lateral excavations (Figure 58b). 
On asmall scale, the initial penetration of the tube into the rock 
would present no problems—there are many commercial cylindrical coring 
augers which can readily trepan to considerable depths with modest power 
requirements (Figure 59). Extending the technique to very large cylinders, 
it is reasonable to consider the details of fitting cutters to the lower edge of 
a cylinder perhaps 30 feet in inside diameter for trepanning several feet into 
the rock. The large area in shear and the high apparent viscosity (Reiner, 
1954) which might be expected would make rotation of the entire cylinder 
difficult, although ways could be visualized to reduce the drag. Pumping 
seawater through orifices near the bottom to the outside, forming a film of 
water along the outside would be an example. This particular configuration 
probably would provide the necessary vertical stability if the sediment were 
fairly viscous; the water would provide the lubricant and the whole assembly 
would perform like a journal bearing. 
7) 
