It is planned to further investigate the current research in rock 
comminution by novel techniques and to prepare one or two requests for 
proposals. If a positive response is obtained from industry, it is planned to 
take the first steps toward developing machines, at first on small scale to 
demonstrate their efficacy. Successful tests will lead to further consideration 
of these advanced techniques for incorporation into the complete construction 
systems. 
LARGE HOLE SEALING AND DEWATERING 
OF CAVITY 
To the potential occupant of an undersea manned station in 
subbottom rock, probably two safety aspects will be of prime interest— 
the integrity of the rock in which the excavation Is made, and the quality 
of the seal at the point of entry to the ocean (A, Figure 57). The variability 
of natural rock makes the former always open to question, but the problems 
of seal leakage are approachable by modern methods of analysis, design, and 
testing. 
Probably largely because the levels of leakage are acceptable and the 
pressures and temperatures are moderate, industrial practice for many years 
has relied on rather simple gasketing, of which that shown schematically in 
Figure 68 is acommon example. Here, a deformable gasket material such as 
rubber, leather, or a semirigid synthetic material is placed in compression by 
a ring of bolts or other confining mechanical device. Aging, prolonged heating, 
oxidation, and other chemical attack usually will change the physical pro- 
perties of the materials used for the purpose and, except for low-pressure 
applications, some leakage usually results. Conformability allows this type 
of gasket to be used with moderately poor surface finish, so the joints are 
comparatively low cost. With increasingly higher pressures and need for 
rapid assembly in high production, industrial gasketing has increasingly 
drifted toward some form of the packing recognized for its unique merits 
by P. W. Bridgeman (Griggs, 1954) of the Massachusetts Institute of Tech- 
nology and developed in many forms for pressures in the thousands of 
atmospheres. This pressurized form of gasket was based on what Bridgeman 
termed the “‘principle of the unsupported area.’’ Griggs (1954) categorically 
stated that only gaskets based on this principle will not leak if the pressure 
is raised sufficiently high. The underlying principle exploited is that of 
having a somewhat deformable or composite gasket loaded on the high- 
pressure side over an area greater than that on the low-pressure side (Figure 
69). 
90 
