Concepts for Rock Fragmentation by High-Frequency 
Vibration 
The possibilities of avoiding use of a high static force or low-frequency 
dynamic force and the attendant heavy machines are especially attractive for 
deep-ocean applications because of the difficulties in reacting large forces on 
unstable ocean bottoms and in lowering heavy machinery from the surface. 
An ideal although probably impractical drilling machine would be light in 
weight, would react against the ocean water, and would have cutters capable 
of effectively destroying competent rock without a high force normal to the 
work face. An additional desirable if not required feature in a large drilling 
machine for subbottom rock drilling would be the lack of a cutter which 
requires replacement or sharpening. A rock fragmenting system which would, 
for example, destroy the surface by the application of high-frequency vibration 
or a series of high-velocity water jets illustrates the ideal. Neither rotational 
torque nor penetration force would be large—the system would probably also 
be small in dimension normal to the rock face, allowing easier access and more 
space for particle removal, pumps, etc. A simplified version of such a machine 
is shown schematically in Figure 56. The same or perhaps greater benefits 
would accrue from use of a similar machine in the subbottom lateral excavation 
(Figure 61) because of the difficulty of assembling and manipulating the typical 
long boring machine in close quarters. 
A quotation from page 54 of the National Research Council report 
(1968) corroborates views presented above: 
Present designs involve massive structures with accompanying problems 
of lack of flexibility, high capital cost, difficult maintenance, etc. One 
method of reducing this could be to introduce percussive energy through 
high frequency, low energy blows. Successful application of such new 
techniques would lengthen cutter life and lessen the thrust, currently 
needed. 
Identical forces applied statically and dynamically result in stresses 
that differ for elastic materials by a factor of two, with the higher values 
resulting from high dynamic load rates. Thus a 100% increase in efficiency 
might be anticipated in a mechanism which could capitalize on this difference 
in resulting stresses. It would be important that the load be applied significantly 
faster than the propagating mechanism could remove the energy within the rock. 
The velocity of the indentor must exceed some critical value of velocity for each 
rock. Determination of these values awaits suitable experiments with various 
rock types. 
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