12
CASE STUDY 12 · INTEGRATED MINING AND PROCESSING
The formula that holds the roof up
Most of South Africa’s underground coal stands on pillars, and every pillar stands on one empirical strength formula. We kept that formula honest, and mapped the century-old workings nobody wrote down.
1 formula
the empirical pillar strength formula the industry designs by
100+ years
of undocumented workings under the coalfields
2 methods
surface geophysics and records work to map old bords and pillars
2018
regional collapse mechanisms simulated for pillar design
01
The problem
Standing on the unknown
Bord and pillar mining leaves the roof standing on coal. Design the pillars too small and sections collapse, sometimes regionally. Design them too big and reserves are sterilised. The strength formula that balances those risks is empirical: it is only as good as its database of failed and intact cases. And beneath the modern workings lie a century of old ones, many unmapped, waiting for a continuous miner to find them the hard way.
“Update of the coal pillar database, strength formula and probability of failure for South African coal mining.”
The 2011 report title. Eleven words carrying every underground roof in the country.
02
The research
Keep the database honest, map the dark
The 2011 update refreshed the pillar database, the strength formula and the probability of failure for South African conditions, with Mathey’s parallel work reviewing failed and intact cases. Project 2.5.7 then pushed design further, simulating regional collapses in bord and pillar workings and testing how much more of the reserve can be safely taken. On the mapping front, Michael van Schoor’s geophysics under Project 1.3.4 tested how to find old pillars from surface, and the bords and pillars mapping work was revisited in 2019 to keep the record current.
M. van Schoor
CSIR. Mapping pillars from surface.
M. Mathey
Pillar failure database and probability of failure.
Coaltech Mining Committee
Programme oversight.
1 formula
between the coal roof and the crews beneath it. We keep it honest.
03
The impact
Quiet, which is the point
Nobody celebrates the collapse that did not happen. The formula, kept current, sits inside every underground design; the collapse simulations inform how far pillar extraction can go; and the mapping work means fewer machines cut into voids nobody recorded. This is the least visible work we fund and among the most consequential.
2011
The update
Pillar database, strength formula and probability of failure refreshed.
2016
Improved utilisation
Project 2.5.7 tests safe extraction of more of the reserve. Van Schoor maps pillars from surface.
2018
Collapse mechanics
Regional collapses in bord and pillar workings simulated for design.
2019
The record kept
Mapping of old bords and pillars revisited and updated.
The evidence. Every claim traces to a published report.
PDFUpdate of coal pillar database, strength formula and probability of failureWhat this report showsThe refreshed empirical basis for South African pillar design.2011Open in the Library → PDFTowards the failure probability of coal pillars, M. MatheyWhat this report showsFailed and intact cases reviewed for the probability model.2011Open in the Library → PDFProject 2.5.7: Improved Utilisation of Underground ReservesWhat this report showsHow much more of the reserve can be taken safely.2016Open in the Library → PDFProject 2.5.7: Quantitative pillar design, simulation of regional collapsesWhat this report showsCollapse mechanics simulated for bord and pillar workings.2018Open in the Library → PDFProject 1.3.4: Mapping Pillars from Surface, M. van SchoorWhat this report showsGeophysics for finding what the old records missed.2016Open in the Library → Where this goes next
The mapping science meets the safety programmes underground. Related: Continuous Miner Safety. Refuge Bays. Kloppersbos.
