Rock excavation 249The fundamental process of excavation, for civil or mining engin-
eering, is to alter the rock block size distribution from the natural,
pre-existing rock blocks to the fragments required for excavation, as
indicated in Fig. 15.2. The energy required for this process is the energy
required to create the new fracture surfaces, together with energy lost in,
for example, stress waves and heat.
Rock can be excavated by explosives or by machines. With explosives
(Fig. 15.3a) the excavation process is cyclical: the energy is put into the
rock in seconds via detonation of the explosives, the gases have to be
Figure 15.3 (a) Blasted rock at quarry face. (b) Tunnel bored by machine.