Australian data range between
19 and 134. Depending on the
roadway’s angle of intersection
with the cleat and the presence or
otherwise of claybands in the seam,
as a general rule, a RRI of <50 is
associated with good rib
conditions, >50 – 75 good to
moderate rib conditions, >75 – 150
moderate to poor rib conditions and
>150 poor to very poor rib
conditions.
The installed rib support capacity
(PRDI) is captured on the vertical
axis and is calculated similarly to the
roof, except the height of the rib is
used instead of roadway width. The
PRDIs in the database range between
0 and 0.55 MN/m. The dataset results
in a favourable R-squared value of
0.62.
In regard to rib bolt length, the
database indicates that, as RRI
increases, longer rib bolts are
generally required (Figure 10). This is
almost certainly related to the fact
that, under higher vertical loads, the
b
increases.
Conclusion
The use of empirical databases can
provide a practical method to help
arrive at the minimum densities of
primary ground support required
during roadway development. This
article focused on the use of Golder’s
Primary Roof Support and Primary
Rib Support databases.
The main drivers of roof
behaviour in coal mines are
considered to be the
in situ
stress
conditions and roof competency.
Depending on these factors, the two
roof failure mechanisms are
bending/block type failure and
buckling type failure. In order to
arrive at a minimum density of
primary roof support required to
help control these types of failures,
the database assesses the roof’s Stress
Strength Ratio (SSR).
In regard to the ribs, the main
failure mechanism has been assessed
to be buckling of the column under
vertical loading. The Primary Rib
Support Database assesses the rib’s
RI) in order to
arrive at an acceptable level of rib
support. The RRI is a function of
depth of cover, roadway height and
the average
in situ
coal strength.
References
1. PENG, S.
Coal Mine Ground Control
(John
Wiley & Sons; 1978).
2. BRADY, B.H.G. and BROWN, E.T.,
Rock
Mechanics for Underground Mining,
3
rd
ed.
(
Kluwer Academic Publishers; 2004).
3. GOODMAN, R.E.
Introduction to Rock
Mechanics
, 2
nd
ed.
(
John Wiley & Sons;
1989) .
4. O’BIERNE, T., SHEPHERD, J.,
RIXON, L.K. and NAPPER, ‘A.
Instability and Support of Coal Mine
Ribs‘, ACIRL Published Report 87 – 3,
(1987).
5. COLWELL, M., ‘Rib Support Design
Methodology for Australian Colliers’,
ACARP Research Project C11027
(2004).
6. HEBBLEWHITE, B.K., WALKER, R. and
LIN, B., ‘Rib Mechanics and Support
Systems’, ACARP Research Project C3059
Final Report (1998).
7. MARK, C. and GADDE, M., ‘Global
Trends in Coal Mine Horizontal Stress
Measurements’, presentation given at
27
th
International Conference on Ground
Control in Mining
(2008).
8. MCNALLY, G.H., ‘The Prediction of
Geotechnical Rock Properties from
Sonic and Neutron Logs’,
Exploration
Geophysics
21.2 (1990), pp. 65 – 71.
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