Page 363 - Rock Mechanics For Underground Mining

MATERIALS AND TECHNIQUES

Figure 11.30 Reinforced haulage at
a depth of 1540 m following a seismic
event of magnitude 4.0. Severely dam-
aged rock is well contained by mesh
and rope lacing (after Ortlepp, 1983).

districts such as those in Western Australia and Ontario, Canada, mining regulations
and codes of practice now require some form of surface support, usually mesh, to
be used in all personnel entry excavations. In Western Australia, the code of practice
applies to all headings that are higher than 3.5 m and requires that surface support be
installed down to at least 3.5 m from the floor (Mines Occupational Safety and Health
Advisory Board, 1999).
In underground metalliferous mining, rock blocks or fragments of fractured rock
are often held in place by a pattern of hoist rope lacing installed between rockbolts
or anchor points. Rope lacing may be used to stiffen mesh in those cases in which
the mesh is unable to provide adequate restraint to loosened rock. Ortlepp (1983,
1997) gives a number of examples of the use of mesh and lacing in conjunction with
rockbolts and grouted cables and steel rods to stabilise tunnels in the deep-level gold
mines of South Africa. Figure 11.30 shows the appearance of an intensively reinforced
haulage at a depth of 1540 m following a seismic event of magnitude 4.0 which had
its source on a fault intersecting the haulage near the location of the photograph. The
haulage was reinforced with 2.5 m long grouted steel rope tendons and 7.5 m long
3
prestressed rock anchors which provided an overall support capacity of 320 kNm .
The 3.2 mm diameter by 65 mm square galvanised mesh was backed by 16 mm
diameter scraper rope. Across the intersection with the fault, the severely damaged
rock was well contained by the mesh and lacing even though several of the prestressed
anchors had failed.
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