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Geotechnical Engineering > Coal Pillar Lecture Notes > Flashcards

Coal Pillar Lecture Notes Flashcards

1
Q

What can underground mining accidents cause (geology)

A

Severe windblast and seismic activity

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2
Q

what has reduce the fatalities in Australia when mine failures occur

A

That the events occured over shut down periods

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3
Q

What are the key differences between mining and other engineering structures

A

Mining changes the loading conditions of the rock mass and does not have consistent well defined properties.

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4
Q

What were the fundermental principles of the research undertaken to address the intrinsic properties of rock mass

A
  1. identification of the primary variables
  2. pysical processes involved in the failure
  3. reviews of field performance where operating mines are utilising full-scale mine testing
  4. undertake rigerous probalistic analysis to quantify levels of risk
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5
Q

What are not deemed appropriate design tools on their own?

A

Trial and error, curve fitting and experimental panels are not adequate on their own.

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6
Q

What is it essential to understand to design appropriate pillars in coal for the risk levels

A

understanding the functions of each pillar system

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7
Q

What are pillar systems for local support

A

*bord and pillar
*pillar extraction (face line pillars, stooks and fenders)
*retreat longwall (chain pillars, sacrificial pillars)
*special purpose

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8
Q

What are pillar systems providing regional stability

A

interpanel pillars
barrier pillars

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9
Q

What are the main function of the pillars in a bord and pillar system

A
  1. restrict surface movement
  2. protect infrastructure from high load abutment stresses
  3. prevent hydraulic connections of overhead water sources going through the strata
  4. provide temporary support of the roof in thick seam workings
  5. provide partitions to ventilation
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10
Q

What are the two pillar extraction methods

A

Face line pillars
Stooks and fenders

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11
Q

What are face line pillars utilised for

A

control abutment stresses around the goaf edge
through
1. act as a leverage point to break off roof strata
2. protect access and egress paths
3. act as venitalion partitions

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12
Q

What are stooks and fenders implemented for

A
  1. control convergence through reducing roof span
  2. function as temporary roof supports
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13
Q

What are the retreat longwall pillar types

A

Chain pillars
Sacrificial pillars

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14
Q

What are chain pillars used for

A
  1. protect future roadways from high abutment stresses
  2. protect access and egress to coal face
  3. act as bentialtion parititons
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15
Q

What is the purpose of special pillars

A
  1. create protective pillars below specific surface features (like dams and cliff faces)
  2. shaft pillars
  3. crown pillars
  4. yeild pillars
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16
Q

What pillars provide regional stability

A

Inter panel pillars
barrier pillars

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17
Q

What do inter-panel pillars control

A
  1. ventilation control
  2. regional instability control
  3. water control
  4. pressure outburst control
  5. fire control
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18
Q

What to barrier pillars provide

A

a regional load bearing framework to the mined to create a buffer for:
*mininimising adjacent mine holing into each other
*protect from risks of other mines (water, fire, gases)
*restrict stresses between collieries
*protect critical mine infrastructure

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19
Q

How is stress transferred over an excavation

A

The weight is transfered to the abutments, this weight increases as excavation width increases. As futher increases the roof might cave.
When excavation becomes very large centre excavation stress is transferred through goaf while edges still support some undermined sections

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20
Q

What does the stiffness of the roof strata control

A

Influence on the magnitude and distribution of the abutment stresses around the excavation

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21
Q

What determines the roof strata stiffness

A

modulus of elasticity, panel width, depth, thickness of roof strata

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22
Q

How do typical panels seperated by a barrier pillar have the abutment stresses interact

A

They dont interact

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23
Q

What happens with the stress in addtional ‘normal’ panels

A

as pillar width decrease there is a relation to other abutment stress profiles. The profiles are additive and result in an increase in pillar stress.

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24
Q

What does width height ratio govern

A

the stiffness and strength of the pillar

25
Q

What occurs with stresses when roadways are very close together creating a small pillar between

A

The small pillar will yeild as it is so narrow it will start to unload and transfer the stress to the abutments

26
Q

What are the two pillar failure modes

A

gradual and controlled
sudden and uncontrolled

27
Q

If the failure of a pillar can be controlled what may be formed

A

a yield pillar may be formed

28
Q

How can major interactions be controlled

A

*roadway width
*rib control
*roof control

29
Q

What is it essentials for the database

A

reliable database of both failed and unfailed pillars

30
Q

What does the coal pillar system comprise of

A

pillars, roof, floor, and contact surfaces

31
Q

How are pillar failure initiated

A

failures initiated by roof and floor failure and they develop gradually

32
Q

What occurs when the pillar suddenly collapses

A

it occurs when the pillar itself fails

33
Q

How will a pillar failure appear

A

may still appear intact

34
Q

what happens to the stress when the pillar fails

A

load is reduced on the overburden and is then transferred to adjacent pillar

35
Q

What is the domino effect

A

if adjacent pillars are already highly loaded any increase may have the effect of transferring the additional load it may also fail. This results in failures are sudden rather than gradual.

36
Q

What are a means of controlling pillar failure progression

A

barrier pillars

37
Q

How is managing of the risk done

A

probabilistic design approach

38
Q

What are the key elements to the iterative decision process

A

*Decide tolerable or acceptable levels of risk
*mining dimensions
*pillar load and strength
*pillar FOS
*stability compliance
*operational compliance

39
Q

What is the equation for risk

A

Risk = probability of failure X consequences of failure

40
Q

What does the UNSW pillar design procedure comprise of

A

competent roof and floor strata

41
Q

What are the three main geotechnical decision steps in the pillar design process

A

Pillar working load
Pillar strength
Design Factor of Safety

42
Q

Pillar load is commonly used to describe what

A

pillar stress

43
Q

How does a uniform pattern of pillars distribute the stress

A

shared equally

44
Q

What is Tributary area theory

A

When the layout is regular the overburden supports the load/stress over an area of influence

45
Q

What is the pillar load highly dependent on

A

rate of extraction

46
Q

why does strength decrease in coal or fissure rock (for a fixed shape specimen) as the volume increases

A

as volume increases the amount of irregularities present increase

47
Q

what generate resistance to the lateral expansion of coal under loads

A

friction and cohesion

48
Q

As the w/h ratio increases and the reliance on friction and cohesion diminises what does the pillar rely on

A

becomes dependent on geometry and is less affected by coal properties

49
Q

What is the empirical mechanistic approach

A

utilising methods of statistically based approach that assessed a likelihood of failure

50
Q

While prior studies utilised the minimum width what do new studies consider

A

there is incremental increase in strength for non square pillar and this was accounted for with an effective width

51
Q

What is FOS equation

A

FOS = pillar strength / pillar load

52
Q

what were the steps to the functional approach

A
  1. identify purpose
  2. pillar life expectancy
  3. have acceptable levels of risk and the probability and consequence
  4. Factor of Safety
53
Q

What is a stook pillars purpose and life expectancy

A

Maintain roof control of the goaf and fail once goaf moves through
1-3 days

54
Q

What is a fender pillars purpose and life expectancy

A

goaf edge control, assist break off of roof strata, protect road from goaf induced damage
3-5 days

55
Q

What is a bord and pillar pillars purpose and life expectancy

A

local roof and floor stability, restrict some sub-surface movement
6-12 months (extraction) or 1-5 years (working)

56
Q

What is a chain pillars purpose and life expectancy

A

long term stability, protect sub-surface features and can prevent ventialtion leakage
10-20 years

57
Q

What is a barrier pillars purpose and life expectancy

A

regional load bearing structure, partition for isolation, protection of surface features
1-20 years

58
Q

What is a subsidence pillars purpose and life expectancy

A

protect major sub surface and surface features
Life of the structure up to permeant life

59
Q

what are other consideration for design

A

operational requirements
geotechnical requirements

Geotechnical Engineering (17 decks)

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