A possible alternative which would not require rotation of the long 
cylinder is shown in Figure 60. Here, a large steel tube would be placed by 
gravity or some method of forcing it through the sediment until it contacted 
and rested on the rock interface. A slightly smaller hole would then be tre- 
panned in with a special cutter, which might fit the large boring machine 
eventually used to bore into the rock. A special internal drag cutter or 
grinder would precisely form the grooves, etc., as necessary for grouting in 
the closure head. 
Summary 
For placing large hole borers in the basement rock of the sea bottom, 
it may frequently be necessary to penetrate an overburden of soft or broken 
rock or unconsolidated sediment, using a steel cylinder grouted to the base- 
ment rock. This cylinder might serve to pilot the large hole-boring mechanism. 
This cylinder will probably incorporate a final closure to facilitate approach 
and entry from a small submersible or PTC. It might also serve to carry special 
equipment for pumping, rock discharge, etc. 
power 
cutter 
control 
and power 
— 
Y xX Wi] ta WW] = VN J], 
pilot drill 
i) 
i) 
formed drag | 
cutter 
Wy 
IN 
Figure 60. Concept of a specialized machine to produce precise smooth groove 
for setting a steel liner in bedrock. 
74 
