FEATURES
Coal cannot be mined from
underground without supporting
the roof and often the sides of
the mining shafts.
they are not complicated and easy to use. When
explaining the split props, the article mentioned that
they would normally conform to the same standards as
round props. Depending on the original diameter, spilt
props are halved or quartered. This makes them
versatile enough to be used for other functions such as
wheel chocking and lagging. According to the three
authors, lagging is described as having similar
dimensions to planks which are used for shoring sides
of mine entries, shafts and haulage ways. Lagging can be
stacked in two ways: lengthwise or crosswise on top of
crossbars for roof support.
Another category of timber product is a header which
functions as a bearing surface against mine roofs. Also
known as caps, headers are ‘conventionally mounted in
props to fill gaps and tighten the wood structure into the
mine roof’. The article highlights that headers can be
replaced by metal.
Some timber products serve more of a support
function and are used together with other timber
products. Crossbars are an example of supporting timber
products, where they are usually used along with props
and headers. ‘They help support the mine roof by
spanning two parallel mining props,’ the article states.
The article also mentions that it is possible to
rehabilitate some wood products for other uses as well.
For example, ties which can be used for railway support,
but also provide a large bearing surface against a soft or
muddy surface. In addition, after being rehabilitated,
ties can also be sawn and sacked similar to crib blocks
and be used for pillar support.
The last timber product described by the journal is a
wedge which is described as a pie-shaped wood slab.
Typically, the slabs are sawn at the mill and then
wedged on top of headers to tighten the props to the
mine roof. ‘Coal mines keep a large supply of wedges
on hand since they can be used for any purpose
requiring tightening or blocking of a support structure,’
the article says.
SOURCES
• ‘The design of pillar systems as practised in
shallow hard-rock tabular mines in South Africa’ by
MU Ozbay, JA Ryder and AJ Jager.
• ‘A look at the Mine-Timber Market in the
Appalachian Bituminous Coal Region’ by Robert
Knutron.
• Wood products use by coal mines’ by Robert Stone,
Christopher Risbrudt and James Howard.
www.timberiq.co.za
// JUNE / JULY 2019 33