Table 2.

Types and methods of coal mining and associated land-use issues

Type of mining (period used)LocationMethodLand-use issues
Crop working (Middle Ages and earlier)Exposed coalfieldDirect working of coal at surface(1) Very shallow workings
(2) Line of subsidence along crop
Bell pits (Middle Ages)Wollaton, Trowell, StrelleyShaft c. 1.25 m diameter, up to 12 m deep; radial working to 10 m from shaft(1) Risk of voids remains
(2) Shaft sites poorly known
(3) Shaft infilling variable and doubtfully compacted
Pillar and stall (from 15th to 17th century)Wollaton, Trowell, Strelley, NuthallCoal cut along grid of roads with rectangular pillars left for support(1) Up to 60% coal may be left, so site investigation may not detect workings
(2) Moderately strong overlying beds (such as Cadeby Formation) may have resisted collapse, leaving large voids
(3) Collapse of pillars may result in cavities and breccia pipes in rock above
(4) Shaft sites poorly known
(5) Shafts variably backfilled and doubtfully compacted
Panel working and longwall mining (from 18th century)Progressively deeper workings from collieries on, and later to the east of, exposed coalfieldExtraction along continuous coalface (up to 200 m wide); temporary support of roof then collapse of all except lateral roadways(1) Collapse of face underground produces subsidence and lowering of ground surface; effects usually immediate and assumed to be complete within a few years
(2) Differential subsidence along faults can lead to severe damage
(3) Faults may ‘reactivate’ as a result of minewater rise long after cessation of mining (years to decades)
(4) Minewater rise may result in acidic minewater at surface
(5) Mine gases may be driven ahead of minewater to surface
(6) Variable backfilling and capping procedures applied to shafts
Opencast mining (from 1940s)Wollaton, StrelleyExcavation of pit, extraction of coals; backfill with spoil; restoration of site(1) Compaction may be incomplete locally on earlier sites
(2) Differential settlement possible along sides of former workings
(3) Natural drainage altered