Excavation
7 5 principles
In this chapter, we explain the fundamental principles of rock excavation.
Initially, the excavation process is discussed in its most basic form, i.e.
reaching the post-peak region of the complete stress-strain curve and
altering the in situ block size distribution to the excavated fragment size
distribution. Then the basic principle of blasting rounds is discussed; all
blasting rounds involve a stress wave effect, stress wave reflections at free
surfaces and a gas pressure effect. We highlight the pre-splitting method
of near-surface excavation in which the final face is blasted before the bulk
of the material is removed, in order to produce a boundary across which
fragmentation is reduced. The complementary method for underground
excavation, known as smooth-wall blasting, is also explained.
The principles of excavation using mechanical means, such as picks, discs
and buttons, on partial- and full-face excavation machines are explained.
The use of such machines within the excavation system is considered to
demonstrate how important it is to consider the machine excavation
process within the context of the overall construction strategy. Finally, we
introduce the concepts associated with assessing effects of vibrations
emanating from the excavation process on other structures.
15.1 The excavation process
It is instructive to consider the fundamental objective of the excavation
process-which is to remove material from within the rock mass resulting
in an opening (the geometry of which is set by some operational criteria).
Bear in mind that there are two potential objectives in removing the rock
one is to create an opening; the other is to obtain the material for its
inherent value. Examples of the first case include civil engineering works,
temporary or permanent mine accesses and petroleum wellbores. In the
second case, the material may contain some valuable mineral, or may be
required in toto as, for example, concrete and road building aggregate.
There will be projects where some parts of the work involve permanent
openings and some parts involve temporary openings, e.g. a mine in which
the access/egress through shafts and tunnnels must be by permanent