Rock Mechanics.pdf - Mining and Blasting

Figure 11.31 Toussaint–Heintzmann
yielding arch: (a) cross section;
(b) clamp joint; (c) alternative joint;
(d) arch configuration before and after
yielding; (e) idealised load–radial
displacement response.
ROCK SUPPORT AND REINFORCEMENT
11.6.6 Steel sets
Steel arches or steel sets are used where high load-carrying capacity elements are
required to support tunnels or roadways. A wide range of rolled steel sections are
available for this application. Where the rock is well jointed, or becomes fractured
after the excavation is made, the spaces between the sets may be filled with steel
mesh, steel or timber lagging, or steel plates. Proctor and White (1977) provide the
most detailed account available of the materials and techniques used in providing
steel support.
Steel sets provide support rather than reinforcement. They cannot be preloaded
against the rock face and, as pointed out in section 11.3, their efficacy largely depends
on the quality of the blocking provided to transmit loads from the rock to
the steel set. Steel arches are widely used to support roadways in coal mines where
they are often required to sustain quite large deformations. These deformations may
be accommodated by using yielding arches containing elements designed to slip at
predetermined loads (Figure 11.31), or by permitting the splayed legs of the arches
to punch into the floor. Where more rigid supports are required as, for example, in
circular transportation tunnels, circular steel or concrete sets are used.
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