Future Plans 
The first effort in designing the cylindrical enclosure for sediment 
penetration appears to be an investigation of the potentially severe structural 
problems which will occur upon dewatering and externally loading the cylinder 
because of dimensional change at the steel—rock interface. The nature of these 
structural problems is described in the final section of this report. 
LARGE HOLE PENETRATION OF COMPETENT ROCK 
The central problem of rapid tunneling in rock today is the development 
of rock fragmentation techniques which will allow the use of semiautomated 
equipment of the type shown (Figure 56) in very hard, unfaulted rocks such as 
granite and basalt, to name two of the more difficult. This initial brief study of 
the problems has been greatly facilitated by three recent comprehensive studies 
(National Research Council, 1968; and Nasiatka, 1968). A concise compilation 
of cost data (Hill, 1968) is also very timely, as cost is a major factor. 
Two particularly important points are quoted from the National 
Academy of Science Panel Reports: 
[I] t is clear that material improvement in cost and productivity 
in tunneling must focus on the rock disintegration process. Generally 
rock which is weaker than the usual concrete offers no serious problems 
for any of several well-known methods of disintegration, 
The probable hardness* and compressive strength of rocks in the 
ocean is very high. This is the basis for the proposed type of one-atmosphere 
construction which depends on the strength of the rock to withstand the 
hydrostatic pressure surcharge upon dewatering. If this assumption of the 
ubiquity of hard rock is correct, major improvements in rock disintegration 
methods may be needed before subbottom drilling and excavation can be 
accomplished in any but selected, favorable rock formations. On the other 
hand, a recent survey article (van Andel, 1968) indicates that fairly soft rock 
might be expected near the water—bottom interface in most parts of the world. 
At this stage of investigation, it is necessary to consider all possible contingen- 
cies of rock hardness, including the most difficult to penetrate. 
* |t is generally agreed that hardness and/or compressive strength of rock may not be the 
real criteria for difficulty of fragmentation. The usual small diameter core tool produces 
a cylindrical specimen which is typically tested in axial compression. The tunneling and 
mining industries have related excavation rate to such test results as a convenience, but 
they are searching for a better index, which is badly needed as a basis for research. 
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