BSc Environmental Studies

1
BSc Environmental Studies

• Non-Renewable Resources
• Impacts of Resource Extraction

EV3903 Non Renewable Resources
2
Impacts of Resource Extraction - 1
Introduction - 1

• mining activity has major effect on stability of
  rocks at depth
• probably most intrusive industrial activity in
  terms of penetration of lithosphere
• mine workings can reach depths of hundreds or
  even thousands of metres

• mining changes stress conditions within rocks
  (Fig. 1) - hence their geotechnical behaviour
• mining also affects surface stability
• also leads to landscape changes through extensive
  storage of

• soil
• rock
• ore processing waste

1
EV3903 Non-Renewable Resources
Fig. 1
3
Impacts of Resource Extraction - 1
Introduction - 2

• 4 main impacts of mining

• requirement for large-scale drainage mainly in
  case of subsurface mining

• instability of land surface (Fig. 2) and its
  effects on land use (subsurface mining)
• creation of enormous quantities of waste
  materials (Fig. 3)
• contamination of air, soil and water

Fig. 2


1
EV3903 Non-Renewable Resources
Fig. 3
4
Impacts of Resource Extraction - 3
Introduction - 3

• extent of environmental damage and cost of
  mitigating it site specific
• influenced by local geology, geography and
  climate
• chemistry of deposit and thus its pollution
  potential may also vary considerably
• specific controls are

• number of different metals contained in deposit -
  determines degree of risk of emissions from mine
  area
• characteristics of rock and overburden underlying
  mine area controls

• degree of seepage from unlined mine dumps and
  tailings ponds

EV3903 Non-Renewable Resources
3
5
Impacts of Resource Extraction - 4
Introduction - 4

• degree of neutralisation of acidified water
  emanating from mine wastes
• geographical location of deposit relative to
  urban centres
• topographic location of deposit relative to water
  table (near surface, height above OD)
• climate specifically

• prevailing winds and shelter or exposure of the
  mine area
• total precipitation - weathering and generation
  of acid mine drainage
• aridity - dust

EV3903 Non-Renewable Resources
4
6
Impacts of Resource Extraction - 5
Surface Mining - 1
Blasting - 1

• associated with both surface and subsurface
  mining, but main effects related to surface
  mining (Figs. 4 5)

5
EV3903 Non-Renewable Resources
Fig. 5
Fig. 4
7
Impacts of Resource Extraction - 6
Surface Mining - 2
Blasting - 2

• damage to buildings related to size of charge and
  distance from point of detonation (Figs. 6 7)

Fig. 5
Fig 6.  Probability of damage versus charge and
distance
EV3903 Non-Renewable Resources
6
8
Impacts of Resource Extraction - 7
Surface Mining - 3
Blasting - 3

• damage to buildings classified into three
  categories

• Threshold Damage

• widening of old cracks and formation of new ones
  in plaster

• dislodgement of loose objects

• Minor Damage does not affect strength of
  structure includes

• broken windows,
• loosened or fallen plaster
• hairline cracks in masonry

7
EV3903 Non-Renewable Resources
Fig. 8
9
Impacts of Resource Extraction - 8
Surface Mining - 4
Blasting - 4

• Major Damage seriously weakens structure
  includes (Fig 8)

• large cracks
• shifting of foundations and bearing walls
• distortion of superstructure caused by settlement
• walls out of plumb

• blasting vibrations (Fig. 9) related to

• amplitude
• particle velocity
• acceleration

Fig. 9  Record of typical blasting vibrations
8
EV3903 Non-Renewable Resources
Fig. 8
10
Impacts of Resource Extraction - 9
Surface Mining - 5
Blasting - 5

• particle velocity most closely related to damage
  in frequency range of typical blasting operations
  (Figs. 10 11)

• peak particle velocities of up to 50 mm sec-1
  regarded as safe as far as structural damage
  concerned
• 50-100 mm sec-1 requires caution
• above 100 mm sec-1 - high probability of damage
  occurrence

Fig. 10

9
EV3903 Non-Renewable Resources
11
Impacts of Resource Extraction - 10
Surface Mining - 6
Blasting - 6

• other effects include human discomfort and
  sensitivity (Fig. 12), noise, dust, etc.

Fig. 12
EV3903 Non-Renewable Resources
10
Fig. 11  Particle velocity and damage in basement
walls
12
Impacts of Resource Extraction - 11
Surface Mining - 7
Sand and Gravel Pits

• visual impact - scar on landscape (Fig. 13) -
  generally dont re-vegetate easily
• slopes unstable - slumping and sliding possible,
  but not significant hazard
• abandoned gravel pits commonly used as dumps
  (Fig. 14) - gravel overburden highly permeable -
  leachate percolates rapidly down to water table -
  little attenuation groundwater pollution

11
EV3903 Non-Renewable Resources
Fig. 13
Fig. 14
13
Impacts of Resource Extraction - 12
Surface Mining - 8
Quarries - 1

• visual impact - scar on landscape - bare rock
  (Fig. 15)
• slopes generally vertical - very dangerous (Fig.
  16)

EV3903 Non-Renewable Resources
12
Fig. 15
Fig. 12
Fig. 16
14
Impacts of Resource Extraction - 13
Surface Mining - 9
Quarries - 2

• slopes generally relatively stable, but danger of
  toppling failure (Fig 17)
• quarrying involves blasting - extremely dangerous
  - nuisance effect
• abandoned quarries often become filled with water
  - also major safety hazard (Fig. 18)

13
EV3903 Non-Renewable Resources
Fig. 18
Fig. 17
15
Impacts of Resource Extraction - 14
Surface Mining - 10
Quarries - 3

• abandoned quarries commonly used for dumps
  (landfills) (Fig. 19) - very dubious - all
  overburden stripped off - so no attenuation of
  leachate
• rocks highly fractured due to blasting, - open
  pathways for leachate to percolate down to water
  table - groundwater pollution likely
• even if not used as landfills, infiltrating
  rainwater not purified due to absence of
  overburden

Fig. 14

14
EV3903 Non-Renewable Resources
Fig. 19
16
Impacts of Resource Extraction - 15
Surface Mining - 11
Placer Mining - 1

• removal of material from streambed changes stream
  dynamics
• may lead to severe erosion immediately downstream
  from dredging operation
• enhances flood potential of stream (Figs. 20 21)

15
EV3903 Non-Renewable Resources
Fig. 20
Fig. 21
17
Impacts of Resource Extraction - 16
Surface Mining - 12
Placer Mining - 2

• stream pollution likely due to use of heavy
  equipment, oil etc. during dredging operations
  (Figs. 20 21)
• processing of immense amounts of gravel, sand and
  mud, results in the severe siltation of streams
  and lakes

• particularly damaging in countries such as the
  Philippines, Indonesia, Brazil, etc.
• in one river in Guyana, water undrinkable for 65
  km downstream (Fig. 22)

EV3903 Non-Renewable Resources
16
Fig. 22
18
Impacts of Resource Extraction - 17
Surface Mining - 13
Placer Mining - 3

• pollution damages fish stocks also destroys fish
  habitats and alters migratory patterns (Fig. 23)

EV3903 Non-Renewable Resources
17
Fig. 23
19
Impacts of Resource Extraction - 18
Surface Mining - 14
Solution Mining - 1
Brining - 1

• controlled brining produces stable cavities that
  cause ground subsidence only if allowed to
  coalesce (Figs. 24 25)

EV3903 Non-Renewable Resources
18
Fig. 24
Fig. 25
20
Impacts of Resource Extraction - 19
Surface Mining - 15
Solution Mining - 2
Brining - 2

• wild brining (Fig. 26) less predictable -
  produced large subsidence zones in Cheshire
  saltfield - often elongated over subsurface
  brine streams (Fig. 27)

27
EV3903 Non-Renewable Resources
19
Fig. 26
21
Impacts of Resource Extraction - 20
Surface Mining - 16
Solution Mining - 3
Brining

• room and pillar mining with excessive extraction
  ratios - even more damaging method - eventually
  banned around 1930

• bastard brining - resulted in catastrophic
  formation of sinkholes up to 100m wide and 10m
  deep as remaining pillars dissolved and collapsed
  (Fig. 28) led to major property damage (Fig. 29)

EV3903 Non-Renewable Resources
20
Fig. 24
Fig. 29
Fig. 28
22
Impacts of Resource Extraction - 21
Surface Mining - 17
Solution Mining - 4
Mercury Separation - 1

• mercury pollution due to extraction of gold with
  mercury during placer gold mining (Fig. 30)
• estimated that gold mining introduces 100 tons
  of mercury into Amazon ecosystem in Brazil every
  year
• numerous other streams similarly affected
• mercury accumulates in plants and animals -
  biomagnifies as it rises through food chain
  (Figs. 31 32)

21
EV3903 Non-Renewable Resources
Fig. 30
23
Impacts of Resource Extraction - 22
Surface Mining - 17
Solution Mining - 4
Mercury Separation - 1

• causes severe neurological diseases and birth
  defects in both animals and humans

EV3903 Non-Renewable Resources
22
Fig. 32
Fig. 31
24
Impacts of Resource Extraction - 23
Surface Mining - 18
Solution Mining - 5
Mercury Separation - 2

• mercury poisoning insidious - often occurs years
  after person exposed to metal
• mercury levels in fish in several Amazon
  tributaries and other South American streams now
  exceeds safe levels for human consumption (Fig.
  33)
• mercury poisoning begun to appear amongst native
  and other people living in Amazon riverside
  villages, where fish major food source

EV3903 Non-Renewable Resources
23
Fig. 33
25
Impacts of Resource Extraction - 15
Surface Mining - 13
Solution Mining - 3
Heap Leaching - 1

• permits allowing use of highly toxic cyanide for
  gold treatment readily granted
• in well-constructed and well-managed heap leach
  operations, cyanide can be looped through a
  closed system so that none is lost (Figs. 34 -36)

EV3903 Non-Renewable Resources
15
Fig. 34
Fig. 35
26
Impacts of Resource Extraction - 15
Surface Mining - 13
Solution Mining - 3
Heap Leaching - 1

• in practice cyanide solutions commonly escape -
  enter surface and groundwater
• numerous accidental spills have occurred in US,
  including

• failure of dam on leaching pond -resulted in
  10,000 gallons of cyanide pouring into nearby
  river
• major fish and bird kills due to cyanide leaks
• Summitville Mine disaster

15
EV3903 Non-Renewable Resources
Fig. 36
27
Impacts of Resource Extraction - 15
Surface Mining - 13
Solution Mining - 3
Heap Leaching - 1

• Summitville Mine, Colorado elevation 3800 m
  headwaters of Rio Grande (Fig. 37)
• high snowfall - 7-11 m per year creates
  landslides and avalanches

Fig. 37

• mining began 1985 leach pads 73 acres in area -
  one heap gt 60 m high - 3 m bond posted
• HDPE liner damaged by avalanches during
  construction not repaired
• 1991 very high snowfall - release of excess
  water from snowmelt contaminated with cyanide and
  heavy metals into Alamosa R.

15
EV3903 Non-Renewable Resources
28
Impacts of Resource Extraction - 15
Surface Mining - 13
Solution Mining - 3
Heap Leaching - 1

• all aquatic life for 17 miles downstream
  exterminated
• report on fish kills estimates 20 m clean up
  costs
• 3 days later mine owners walk away

Fig. 38

• forfeiting 3 m bond dont even lock doors
• 1992 - EPA take over Summitville - 200-m gals
  cyanide-laced water in leach pit
• cost to date of cleanup 150 m and still rising
• Clinton signed bill to increase size of
  environmental bonds for mining activities but
  Bush administration has reduced size of bonds

15
EV3903 Non-Renewable Resources
29
Impacts of Resource Extraction - 16
Surface Mining - 14
Solution Mining - 3
Heap Leaching - 2

• sodium cyanide solutions chemically unstable
• cyanide quickly decomposes in surface waters
  where oxygen is plentiful and acidic conditions
  prevail
• cyanide can persist at toxic levels for much
  longer periods in groundwater
• so poses long term threat to water wells used for
  human consumption, livestock and irrigation
• cleanup costs immense - at one major gold mine in
  US, operation running at no profit, only break
  even situation
• decision to keep mine in operation based on fact
  that cheaper to keep it running than closing mine
  down and starting to pay for cleanup

EV3903 Non-Renewable Resources
14
30
Impacts of Resource Extraction - 17
Surface Mining - 15
Open Pit Mines - 1

• visual impact huge hole and enormous surface
  spoil heaps - major scars on landscape (Fig. 39)
• slopes generally very steep- very dangerous

Fig. 39

• slopes designed for stability - but danger of
  oversteepening slopes leads to

• collapse
• sliding failure
• mudflows

• particularly prone if discontinuities (bedding,
  cleavage, joints, faults) dip towards open pit

9
EV3903 Non-Renewable Resources
31
Impacts of Resource Extraction - 17
Surface Mining - 15
Open Pit Mines - 2

• dewatering of mine area - creates cone of
  depression around mine (Fig. 40)
• modifies the hydrogeological regime for mine area
  and perhaps larger region (more later)
• abandoned open pits commonly become filled with
  water - also major hazard (Fig. 41)

EV3903 Non-Renewable Resources
9
Fig. 40
Fig. 41
32
Impacts of Resource Extraction - 17
Surface Mining - 15
Open Pit Mines

• extraction of the ore deposit, exposes sulphide
  minerals to oxygen and water
• results in weathering and oxidation (Fig. 42)
• leads to acidification of surface and groundwater
  and dissolution of heavy metals acid mine
  drainage (AMD - more later)
• contaminates groundwater and standing surface
  water within the open pit e.g. Berkeley Open
  Pit pH 2.5 (Fig. 43)

Fig. 42


9
EV3903 Non-Renewable Resources
Fig. 43
33
Impacts of Resource Extraction - 18
Surface Mining - 10
Strip Mining

• major environmental degradation
• topography altered - land rarely rehabilitated in
  past - now requirement (Fig. 44)

Fig. 44

• abandoned mine area subject to severe soil
  erosion - sediment eroded from spoil banks etc.
  can silt up streams - increases potential flood
  risk
• coal mining wastes highly toxic sulphur, zinc,
  lead, arsenic
• leads to contamination of drainage (both surface
  and groundwater) by base metals and sulphuric
  acid - AMD
• visual impact - spoil banks unsightly and highly
  toxic, so vegetation wont re-establish, even
  after several decades

EV3903 Non-Renewable Resources
18
34
Impacts of Resource Extraction - 19
Subsurface Mining - 1
Mine Drainage Operations - 1

• mine dewatering mainly necessitated for
  underground mining (Fig. 45)
• has objective of protecting shafts and adits from
  flooding
• also required for deep open-pit mining if water
  table relatively close to surface
• pumped water dumped at surface, usually into
  surface streams

EV3903 Non-Renewable Resources
19
35
Impacts of Resource Extraction - 19
Subsurface Mining - 1
Mine Drainage Operations - 1

• leads to changes in hydrogeological conditions -
  have following impacts

• changes groundwater flow dynamics, e.g. flow
  rates and direction - due to creation of
  artificial discharge zone
• change in groundwater recharge - due to
  fluctuation in water exchange rate above water
  table
• change in groundwater discharge - affects
  recharge of surface waters

EV3903 Non-Renewable Resources
19
36
Impacts of Resource Extraction - 19
Subsurface Mining - 1
Mine Drainage Operations - 1

• changes in groundwater regime increase extent of
  interconnection between

• different aquifers
• ground and surface water

• two major consequences

• possible deterioration in groundwater quality
  common when water from various sources mix e.g.
  if dewatered mine area near coast may lead to
  intrusion of highly saline water into aquifer
• may lead to reduction in river discharge - since
  groundwater in high latitude parts of globe feed
  rivers

EV3903 Non-Renewable Resources
19
37
Impacts of Resource Extraction - 20
Subsurface Mining - 2
Mine Drainage Operations - 2

• rivers may become sources of recharge for
  groundwater, reversing the hydrogeological regime
  completely - in the case of small rivers, this
  can lead to them drying out completely and so
  generating intermittent flow
• other impacts of dewatering and changes in the
  hydrogeological regime are

• reduction in soil moisture due to dewatering, may
  affect vegetation
• productivity of agricultural crops may decrease
• drainage of bogs and marshes
• vegetation degradation - will affect the whole
  ecosystem, and the diversity of fish, birds,
  animals and other fauna within the dewatered area
  may be substantially reduced. - thus ecosystem
  degradation from large scale dewatering is
  additional to the impacts on ecosystems of
  chemical contamination from mining activity
• introduction of air into previously saturated
  rocks - triggers or accelerates mineral oxidation
  - accentuates acid mine drainage (AMD)

EV3903 Non-Renewable Resources
20
38
Impacts of Resource Extraction - 21
Subsurface Mining - 3
Mine Drainage Operations - 3

• removal of water from rock pore spaces increases
  the potential for deformation of rock strata
  (consolidation) - pore water pressure (PWP)
  reduction changes the physico-mechanical
  characteristics of rock - stress previously
  accommodated by PWP is redistributed to the
  adjacent rock grains - reduces stability of the
  rocks - impacts on construction stability and
  also agricultural activity in area affected by
  dewatering
• leads to the intensification of karstification
  and suffusion - rate of flow of groundwater in
  the drawdown cone is increased, so

• water exchange is accelerated, leading to an
  increased potential for solution and
  karstification, where the bedrock is limestone,
  e.g. Silvermines
• washes out of fines from unconsolidated sands and
  gravels (suffusion internal erosion)

• openings created by karstification and suffusion
  affect stability of overlying rocks
• local water supplies in dewatered areas affected
  - wells go dry

EV3903 Non-Renewable Resources
21
39
Impacts of Resource Extraction - 22
Subsurface Mining - 4
Mine Drainage Operations - 4

• groundwater extracted during dewatering is
  discharged into surface streams - affects stream
  dynamics - can also affect natural balance of
  ecosystems by changes in river velocity, river
  depth and even the amount of oxygen in the
  discharged groundwater
• chemical composition of groundwater differs from
  that of surface water, so this may also have
  impacts on aquatic flora and fauna
• groundwater may be contaminated with acid mine
  drainage
• finaly, degree of impact of dewatering depends on

• natural (local) hydrogeological conditions
• size of ore body
• depth of ore deposit

EV3903 Non-Renewable Resources
22
40
Impacts of Resource Extraction - 23
Subsurface Mining - 5
Mine Drainage Operations -5
Effects of Water Table Recovery - 1

• abandonment of mining activity and cessation of
  water extraction leads to recovery of the water
  table and progressive flooding of underground
  workings
• rate of recovery depends on permeability of the
  dewatered zone and the size of the depression
  cone (depth and radius)
• original hydrogeological conditions may be
  restored over a period of time but numerous
  environmental problems may be associated with
  flooding of old mine workings

• pollution of water entering old workings, with
  resulting potential pollution of groundwater
  aquifers, possibly used for groundwater supplies
  - also potentially surface waters through springs
  and streams.
• reduction in stability of the mine area, due to
  the influence of the rewatering on

• the mechanical properties of mined out rocks or
  rocks surrounding mine area
• the stability of fine-grained unconsolidated
  backfill deposits

EV3903 Non-Renewable Resources
23
41
Impacts of Resource Extraction - 24
Subsurface Mining - 6
Mine Drainage Operations -5
Effects of Water Table Recovery - 2

• addition of water reduces compressive strength,
  as pore water acts oppositely to normal stresses,
  and reduces the angle of friction on joint
  surfaces

? S0 (? - p) tan?

• estimated reduction in strength of order of 10
  may result
• clay-rich rocks may undergo a reduction in
  physico-mechanical characteristics of up to
  50-70 due to water saturation - become plastic
  and begin to creep, destabilising strata above
  them
• some materials, e.g. fine-grained backfill or
  clays may undergo liquefaction, and become
  displaced towards voids at the bottom of the
  mine, destabilising empty shafts.
• although flooding threatens the stability of mine
  areas already at the limit of their stability, if
  failure does not occur during the flooding stage
  or immediately afterwards, long-term stability of
  area should be enhanced

EV3903 Non-Renewable Resources
24
42
Impacts of Resource Extraction - 25
Subsurface Mining - 7
Land Use and Ground Stability (Subsidence) - 1

• stability of rock subject to mining a function of
  the geotechnical properties of the rock material,
  which are dependent on

• pre-existing stress conditions within the rock
  mass
• rock strength
• rock deformation parameters (i.e. elastic moduli)
• water content

• changes in geotechnical properties of rock due to
  mining considerable - strongly dependent on
  extraction technique.
• in subsurface mining, creation of mine openings
  changes pre-stress conditions within rock mass -
  leads to collapse of rock material into mine
  workings, and displacement of floor, roof and
  walls into shaft space
• process leads to deformation of adjacent rock,
  extent of which dependent on size of mined out
  space, and parameters listed above

EV3903 Non-Renewable Resources
25
43
Impacts of Resource Extraction - 25
Subsurface Mining - 7
Land Use and Ground Stability (Subsidence) - 1


Sag subsidence (left), the most common type of mine subsidence, appears as a gentle depression in the ground and can spread over an area as large as several acres. Collapse of pillars supporting the mine roof is a typical cause. Pit subsidence (right) forms a bell-shaped hole 6-8 feet deep and from 2-40 feet across, and occurs when a shallow mine roof collapses
EV3903 Non-Renewable Resources
25
44
Impacts of Resource Extraction - 26
Subsurface Mining - 8
Land Use and Ground Stability (Subsidence) - 2

• cave-ins give rise to three major zones of rock
  deformation within overlying strata (Fig. 13)

• zone of collapse blocks of rock cave in on mine
  workings (thickness can exceed the thickness of
  the mined area by 3-4 times)
• zone of fractures within which transverse
  (layer perpendicular) and longitudinal (layer
  parallel) fissures form.
• zone of subsidence - - strata are deformed, but
  undergo no fracturing

13

• all rock above the mined area undergoes
  deformation - commonly this may reach surface,
  giving rise to extensive subsidence (more later)

EV3903 Non-Renewable Resources
26
45
Impacts of Resource Extraction - 27
Subsurface Mining - 9
Land Use and Ground Stability (Subsidence) - 3

• extent and character of rock deformation depends
  on geological and technical factors - e.g.

• ore body location
• ore body size
• ore body depth
• presence of weak strata
• geological structure particularly presence of
  faults and fractures
• presence of saturated rock, i.e. within the
  saturated zone
• extraction technique
• strength of backfilling material, where a
  backfill technology is employed

• ground stability ultimately depends on style of
  mining - generally dictated by shape, size,
  depth and value of ore or extractable rock.

EV3903 Non-Renewable Resources
27
46
Impacts of Resource Extraction - 28
Subsurface Mining - 10
Land Use and Ground Stability (Subsidence) - 4
Old Abandoned Mine Hazards

• old mine shafts a widespread hazard in many
  countries - thousands in UK
• small old mines had far more shafts than large
  modern mines - records of old shafts very
  incomplete
• old abandoned shafts abound - mainly 1-5 m in
  diameter and 10-300 m deep
• may be lined with brick, concrete or dry stone or
  may be completely unlined
• loose or uncompacted waste may completely or
  partially fill shafts, or shafts may be empty
• shaft mouths may be closed up with timber, steel
  or concrete or may be left open
• may be overgrown by vegetation, or may be
  properly sealed and capped

EV3903 Non-Renewable Resources
36
47
Impacts of Resource Extraction - 29
Subsurface Mining - 11
Land Use and Ground Stability (Subsidence) - 5
Stoping

• creates large open underground stopes
• subsidence threat localised, but may locally
  sterilise ground directly above mine

Room and Pillar (Pillar and Stall) - 1

• older mines often over-extracted create
  long-term subsidence threat

• better controlled modern mines have no surface
  effects
• old mines commonly undergo roof span failure and
  progressive breakdown of beds causing upwards
  stoping (migration of cavities) - may reach the
  surface to create a crown hole by sudden collapse
  (Fig. 14)

EV3903 Non-Renewable Resources
29
Fig. 14
48
Impacts of Resource Extraction - 30
Subsurface Mining - 12
Land Use and Ground Stability (Subsidence) - 6
Room and Pillar (Pillar and Stall) - 2

• stoping may be stopped by

• beam action of a strong bed
• formation of a stable arch in thinner beds
• support of the roof due to accumulation of debris

• crown holes rare from adits deeper than 30 m or
  10 times thickness of extracted seam
• mine pillars fail where

• they are left too slim,
• are subsequently overloaded
• are subject to weathering and erosion

• multiple domino-style failures may affect large
  areas, and were common in the past due to
  over-extraction and pillar-robbing (Fig. 15)

EV3903 Non-Renewable Resources
30
49
Impacts of Resource Extraction - 31
Subsurface Mining - 13
Land Use and Ground Stability (Subsidence) - 7
Room and Pillar (Pillar and Stall) - 3

• collapse of old mines can be delayed for in
  excess of 100 years
• modern threat of ground failure is minimal where

• mine is gt 50m deep
• any imposed structural load is slight in
  proportion to existing rock overburden
• pillar erosion decreases with depth

Bell Pits

• rarely more than 10m deep - only present a
  localised subsidence hazard
• generally occur in dense groups - must be filled
  or excavated if development over them cant be
  avoided

EV3903 Non-Renewable Resources
31
50
Impacts of Resource Extraction - 32
Subsurface Mining - 14
Land Use and Ground Stability (Subsidence) - 8
Longwall Mining - 1

• total extraction of all coal and removal of roof
  support brings about roof collapse and inevitable
  subsidence displaying well-defined pattern (Fig.
  16)
• roof failure behind longwall face propagates
  upwards and outwards through overlying rock

• geometry function of angle of draw
• varies with rock strength -roughly 30-35?
• increases slightly in weaker rocks

EV3903 Non-Renewable Resources
Fig. 16
32
51
Impacts of Resource Extraction - 32
Subsurface Mining - 14
Land Use and Ground Stability (Subsidence) - 8
Longwall Mining - 1

• other critical parameters, which control
  subsidence movements are

• depth of working (h)
• width of the mined panel (w)
• extracted thickness of coal (t)

• end result of roof failure is subsidence bowl at
  ground surface
• extends 0.7 h outside the panel
• not clearly defined as tapers to zero (Fig. 17)

Fig. 16
32
EV3903 Non-Renewable Resources
52
Impacts of Resource Extraction - 33
Subsurface Mining - 15
Land Use and Ground Stability (Subsidence) - 9
Longwall Mining - 2

• maximum depth of subsidence bowl always less than
  seam thickness
• due to volume increase as cracks open up within
  subsiding rocks
• can accumulate to several metres over time if
  multiple seams worked

• subsidence wave has length of 1.4 h (Fig 18)
• mid-point of maximum tilt and neutral strain
  close to vertically above coal face
• migrates with the advancing face
• also develops to a similar shape over panel sides

EV3903 Non-Renewable Resources
33
Fig. 18
53
Impacts of Resource Extraction - 33
Subsurface Mining - 15
Land Use and Ground Stability (Subsidence) - 9
Longwall Mining - 2

• ground tilt as subsidence wave passes damaging to
  built structures
• also related cycle of surface extension and
  shortening

Fig. 17

• strain and subsidence profiles shown in Fig. 19
• strain profiles show an outer zone of extension
  and inner zone of compression
• line of neutral strain roughly above panel edge
• subsidence and strain most severe over shallow
  wide panels in thick seams

EV3903 Non-Renewable Resources
33
54
Impacts of Resource Extraction - 34
Subsurface Mining - 16
Land Use and Ground Stability (Subsidence) - 10
Longwall Mining - 3

• also complicated by geological factors (faults,
  strong rocks, steep dips) and multiple workings
• subsidence effects more severe with older shallow
  mining than during modern mining of deeper seams

• pattern and timing of subsidence over longwall
  faces is predictable
• so structures at risk can be strengthened before
  mining begins

34
EV3903 Non-Renewable Resources
Fig. 19
55
Impacts of Resource Extraction - 34
Subsurface Mining - 16
Land Use and Ground Stability (Subsidence) - 10
Longwall Mining - 3

• approximate predictions of maximum values of
  subsidence, strain and tilt with respect to h, w,
  and t estimated using graph (Fig. 19)
• typical values shown
• better predictions can be made with graphs for
  specific coalfields, based on coalfield records
  and local rock characteristics

EV3903 Non-Renewable Resources
34
Fig. 19
56
Impacts of Resource Extraction - 35
Subsurface Mining - 17
Land Use and Ground Stability (Subsidence) - 11
Longwall Mining - 4
Example of Calculations   Site factors (from mine
plans) Thickness (t) 1.2 m
Panel Width (w) 160 m Depth
(h) 400 m   Ratios w/h 160/400 0.4
t/h 1.2/400 0.003 Reading off
graph for value of w/h 0.4  


EV3903 Non-Renewable Resources
35
57
Impacts of Resource Extraction - 35
Subsurface Mining - 17
Land Use and Ground Stability (Subsidence) - 11
Longwall Mining - 4
  Subsidence Factor (direct from graph) s/t
0.3 Subsidence (s) 0.3 x t
0.3 x 1.2 0.36 m 360 mm Extension (E)
0.28 (from graph) x t/h 0.28 x 0.003
0.00084 Compression (C) 0.62 (from graph)
x t/h 0.62 x 0.003 0.00186 Strain
E C 0.00084 0.00186 0.0027
2.7 mm/m Tilt 1.4 (from graph) x t/h
1.4 x 0.003 0.0042 1 in 238


EV3903 Non-Renewable Resources
35
58
Impacts of Resource Extraction - 36
Subsurface Mining - 18
Land Use and Ground Stability (Subsidence) - 12
Longwall Mining - 5

• scale of subsidence problem illustrated by extent
  of surface depression due to subsidence in coal
  mining regions of former USSR
• areas gt 200 km2 affected in Donbass Basin,
  Ukraine and Chelibensk Province
• instability and subsidence problems in
  underground mining eased by choice of appropriate
  mining method - so deformational stress brought
  about by ore extraction does not exceed strength
  of the rocks
• backfilling technology can increase stability of
  many underground mines - perhaps combined with
  room and pillar approach.

EV3903 Non-Renewable Resources
36
59
Impacts of Resource Extraction - 37
Subsurface Mining - 19
Wastes Storage and Landscape Degradation - 1

• wastes include

• overburden from surface mining
• broken and discarded rock dumped in spoil heaps
• tailings emplaced in dumps or ponds
• slags from smelters

• mine wastes represent the highest proportion of
  waste produced by any industrial activity -
  billions of tonnes produced annually

EV3903 Non-Renewable Resources
37
60
Impacts of Resource Extraction - 37
Subsurface Mining - 19
Wastes Storage and Landscape Degradation - 1

• due to its high volumes, mine wastes historically
  has been disposed of

• at lowest possible cost
• without regard to safety
• with considerable environmental impact
• with extreme landscape degradation

EV3903 Non-Renewable Resources
37
61
Impacts of Resource Extraction - 38
Subsurface Mining - 20
Wastes Storage and Landscape Degradation - 2
Fig. 20

• surface mines produce per ton of ore 8 x waste
  of subsurface mines
• grade of ore determines quantity of waste
  produced (Fig. 20)
• at Cu ore grades of 0.9
• to produce 9 million tonnes of Cu
• 990 million tonnes of ore must be extracted

EV3903 Non-Renewable Resources
38
62
Impacts of Resource Extraction - 38
Subsurface Mining - 20
Wastes Storage and Landscape Degradation - 2

• gold mining requires processing of even greater
  quantities of material to obtain very small
  quantities of metal 325,000 tonnes of Au ore
  for only 50 kg of Au
• 50 billion tonnes of mining waste in US alone
• create mountains of spoil heaps covering
  extensive areas of land, withdrawing them from
  agricultural and forestry activities
• in Poland, surface mining has resulted in
  destruction of agricultural land by

1975 1980 25,000 ha
56,000 ha

• in Germany, by 1985, coal mining had led to a
  reduction in

• agricultural land - 32,000 ha
• forestry land - 9,000 ha

EV3903 Non-Renewable Resources
38
63
Impacts of Resource Extraction - 39
Subsurface Mining - 21
Wastes Storage and Landscape Degradation - 3

• type of waste rock disposal facility depends on
  topography and drainage of site and volume of
  waste
• in terms of coarse mine waste - disposal can be
  classified as

• valley fills
• side-hill dumps
• open piles

EV3903 Non-Renewable Resources
39
64
Impacts of Resource Extraction - 39
Subsurface Mining - 21
Wastes Storage and Landscape Degradation - 3

• valley fills normally commence at upstream end of
  valley and progress downstream
• side-hill dumps constructed by placement of waste
  along hillsides or valley slopes - avoid natural
  drainage courses
• open piles tend to be constructed in relatively
  flat lying areas due to their upstanding
  nature, subject to intense erosion - visually
  highly intrusive

EV3903 Non-Renewable Resources
39
65
Impacts of Resource Extraction - 40
Subsurface Mining - 22
Wastes Storage and Landscape Degradation - 4

• spoil heaps also highly toxic - contain
  significant contents of pyrite and other heavy
  metal-bearing sulphide minerals
• also highly permeable - so drain relatively
  rapidly
• dont vegetate easily due to their toxic nature
  and low moisture content
• dry out readily - so highly susceptible to wind
  erosion
• spread toxic dust and contaminate surrounding
  land for miles around, e.g. Silvermines 1983
• acid mine drainage (AMD) from spoil heaps another
  major environmental problem

EV3903 Non-Renewable Resources
40
66
Impacts of Resource Extraction - 41
Subsurface Mining - 23
Wastes Storage and Landscape Degradation - 5

• important factor in construction of spoil heaps
  is their long-term stability
• tip failure at Aberfan, Wales in 1966 an example
  of many similar colliery tip failures
• had tragic consequences - buried village school
  killing 112 children

• instability arose from poor siting of a series of
  tips over natural springs on the valley slopes
  (Figs. 21 22)
• lubricated base of tips

EV3903 Non-Renewable Resources
41
Fig. 21
67
Impacts of Resource Extraction - 41
Fig. 21
Subsurface Mining - 23
Wastes Storage and Landscape Degradation - 5

• several previous failures in these tips had same
  cause
• on this occasion, during wet weather, tip 7
  underwent rotational slip

• unable to drain due to saturated nature - result
  of fine-grained impermeable nature of spoil
• degenerated into flow slide and finally mudflow
• travelled almost 1 km down valley side and into
  village

EV3903 Non-Renewable Resources
41
Fig. 22
68
Impacts of Resource Extraction - 42
Subsurface Mining - 24
Wastes Storage and Landscape Degradation - 6

• tailings - fine-grained slurries
• formed from crushed rock from which ore separated
  - or produced by washings from coal mines
• deposited as slurry generally in specially
  constructed tailings dams - usually confined by
  embankment dam
• contain high proportions of pyrite, heavy metals
  and other toxic chemicals
• source of AMD if seepage occurs - from their
  base, if unlined - through dam wall
• failure of tailings dams another potential
  catastrophe - occurred after heavy rains at
  Buffalo Creek, West Virginia, 1972 - over 1500
  houses destroyed - 118 lives lost

EV3903 Non-Renewable Resources
42
69
Impacts of Resource Extraction - 43
Subsurface Mining - 25
Wastes Storage and Landscape Degradation - 7

• resulting dereliction of land and overall
  environmental degradation due to such disasters
  more difficult to assess
• derelict land defined as land so damaged by human
  activity as to need remedial treatment before
  further use
• in England, mineral extraction responsible for
  more derelict land than any other single activity
  (Fig. 23a)

23
EV3903 Non-Renewable Resources
43
70
Impacts of Resource Extraction - 43
Subsurface Mining - 25
Wastes Storage and Landscape Degradation - 7

• in 1988 derelict areas made up of

• spoil heaps - 30
• excavations -15
• mining subsidence - 2.5

• extraction-related derelict land decreasing
  steadily - from

• estimated 25,000 ha (64 of total) in 1969
• 19,000 ha (47.5) in 1988

• so derelict land being reclaimed faster than its
  being produced by closure of pits, mines and
  quarries (Fig. 23b)

EV3903 Non-Renewable Resources
43
71
Impacts of Resource Extraction - 44
Subsurface Mining - 26
Wastes Storage and Landscape Degradation - 8

• net annual reclamation only small proportion of
  total derelict areas
• order of 50 years or more before all land
  reusable
• new extraction permits subject to more stringent
  restoration conditions than old licences
• inadequate reclamation conditions still apply to
  gt ? of 96,000 ha permitted surface workings in
  England - mostly for construction materials (Fig.
  24)

24
EV3903 Non-Renewable Resources
44
72
Impacts of Resource Extraction - 44
Subsurface Mining - 26
Wastes Storage and Landscape Degradation - 8

• these sites will add to stock of derelict land
  when present working finishes
• underground mining permits affect at least 8 x
  area of surface licences
• licences require compensation for subsidence
  damage.
• but water pollution from AMD not covered
• rapid closure of coal mines in Britain likely to
  exacerbate this problem

EV3903 Non-Renewable Resources
44