Page 330 - Rock Mechanics For Underground Mining

11 Rock support and reinforcement

11.1 Terminology

The term support is widely used to describe the procedures and materials used to im-
prove the stability and maintain the load-carrying capability of rock near the bound-
aries of underground excavations. As will be shown in this chapter, the primary
objective of support practice is to mobilise and conserve the inherent strength of the
rock mass so that it becomes self-supporting.
In accord with modern practice particularly in Australia, a distinction will be made
between the terms support and reinforcement, using the definitions introduced by
Windsor and Thompson (1993). Support is the application of a reactive force to
the surface of an excavation and includes techniques and devices such as timber, fill,
shotcrete, mesh and steel or concrete sets or liners. Reinforcement, on the other hand,
is a means of conserving or improving the overall rock mass properties from within
the rock mass by techniques such as rock bolts, cable bolts and ground anchors.
It was once the custom to describe support as being temporary or permanent. Tem-
porary support was that support or reinforcement installed to ensure safe working
conditions during mining. For centuries, such support consisted of some form of tim-
bering. If the excavation was required to remain open for an extended period of time,
permanent support was installed subsequently. Quite often, the temporary support
was partly or wholly removed to enable the permanent support to be installed. As
will be demonstrated in section 11.2, this practice negates the advantage that can be
obtained by applying the principles of rock–support interaction mechanics and so
should be avoided.
Modern practice is to describe the support or reinforcement of permanent exca-
vations as being primary or secondary. Primary support or reinforcement is applied
during or immediately after excavation, to ensure safe working conditions during sub-
sequent excavation, and to initiate the process of mobilising and conserving rock mass
strength by controlling boundary displacements. The primary support or reinforce-
ment will form part, and may form the whole, of the total support or reinforcement
required. Any additional support or reinforcement applied at a later stage is termed
secondary.
It was once common practice to regard stopes as temporary excavations having
different support requirements from the more permanent mine installations such as
major access ways, haulages, crusher chambers, workshops, pumping stations and
shafts. Indeed, this distinction may still be made, particularly in the mining of narrow
orebodies where the support techniques used in the vicinity of the face may be quite
different from those used for permanent mine installations. However, many large-
scale metalliferous mines now use mechanised stoping methods in which individual
stopes may be very large and may have operational lives measured in years rather
than weeks or months. In these cases, the support and reinforcement techniques used
may have much in common with those used for permanent mine installations and in
civil engineering construction.

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