4, 
A crushed and compacted 
(Reprinted from an article by 
H. L. Hartman, ‘‘Basic Studies 
of Percussion Drilling,’’ Mining 
Engineering, Vol. 11, no. 1, 
January 1959, p. 68-75.) 
Figure 62. Chip formation by a 
Novel Drilling Techniques 
Known approaches to 
nonconventional drilling and frag- 
mentation of rock have been recently 
summarized by Maurer (1968). This 
section discusses those methods which 
appear to have merit for deep-ocean 
drilling. 
Nonconventional approaches 
can be grouped into four categories, 
according to the method of inducing 
local stresses in a rock mass, or other- 
wise destroying its competent structure: 
percussive drill bit 
(Hartman, 1959). 
A 1. Mechanically induced stress 
K . Thermally induced stresses 
2 
(a) Sharp indentor . . 
3. Fusion and evaporation 
4 
. Chemical disintegration 
Because of the presence of 
high-pressure seawater at the drilling 
site, items 2, 3, and 4 do not appear 
to have merit for making the initial 
penetration into the ocean bottom. 
Some might be considered for lateral 
excavation in a sealed-off, one- 
atmosphere environment but would 
probably be undesirable because of 
their potentially toxic effect on the 
cavern’s atmosphere. Spalling by an 
electrically heated plasma torch 
might be an exception, since it does not involve combustion but could use 
electrical energy. The important approaches to mechanically inducing stresses 
are discussed below. 
(b) Blunt indentor 
(c) Blunt indentor 
Figure 63. Proposed method of rock 
failure under sharp and 
blunt indentors. 
High-Pressure Water Jets or Erosion Drills. With sufficiently high 
velocities, jets of water are able to spall the hardest rocks without the use 
of abrasives. Ostrovskii (1962) and Zelenin et al. (1958) report on a four- 
nozzle drill with 1-mm nozzles delivering water at a pressure of 1,000 
atmospheres and drilled granite at 15 cm/min. Maurer (1968) cites many 
80 
