1 Raise Caving—A Novel Mining Method
1.1 De-stressing Phase
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Control of stresses
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Control of seismicity
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Control of hangingwall caving
1.2 Production Phase
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Extraction by active drilling and blasting from a production raise being situated in a stress shadow of an adjacent slot
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Pillar crushing and de-stressing by decreasing of the pillar width to effective height ratio due to stope extraction behind adjacent de-stressing slots
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A combination of the above-mentioned possibilities
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Pre-conditioning of the pillar could be used to facilitate pillar crushing
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Pillar crushing could also be facilitated due to high abutment stresses near stoping areas
1.3 Dynamic System
1.4 Advantages of Raise Caving
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Active stress control approach
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Modern raise mining techniques
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Potential for automation and remote control
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Potential for just-in-time infrastructure development
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Flexibility on short to medium term
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Adaptability to different conditions and requirements
1.5 Generic Layout Options in Raise Caving
2 Modelling Approach
2.1 Numerical Simulation Approach
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Easier interpretation of results
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Fewer and simpler input parameters
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Quick results of stress and deformations
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Simple implementation of pillar behavior (stress-strain curves)
2.2 Model
Input parameter | Value |
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Young’s modulus [GPa] | 53 |
Poisson’s ratio [−] | 0.32 |
Geometry parameter | Value |
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Pillar Width Wp [m] | 20, 30, 50, 70, 100 |
Pillar height = Slot thickness Hp = Hs [m] | 10 |
Slot width Ws [m] | 20, 30, 50, 70, 100 |
Inclination In [m] | 65° |
Stope width Wst [m] | 20, 30, 50, 70, 100 |
Stope height Hst [m] | 50 |
Slot length = Pillar length = Stope length L [m] | 400 |
Stress direction | Primary stresses—Sandström 2003 [MPa] | Primary stresses—LKAB 2022 [MPa] |
---|---|---|
\(\sigma _{v}\) | 58 | 58 |
\(\sigma _{H\_ EW}\) | 74 | 74 |
\(\sigma _{H\_ NS}\) | 56 | 74 |
2.2.1 Implementing Pillar Yielding and Crushing
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Young’s modulus
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Pillar strength
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Post peak modulus
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Pillar residual strength
Parameter set | Behavior | W/H | Young’s modulus [GPa] | Peak strength [MPa] | Post peak modulus [GPa] | Residual strength [MPa] |
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Low Residual Strength | Strain softening | 2 | 40 | 88 | −25 | 4 |
Medium Residual Strength | Strain softening | 2 | 40 | 88 | −22 | 6 |
High Residual Strength | Strain softening | 2 | 40 | 88 | −19 | 9 |
Low Residual Strength | Strain softening | 3 | 40 | 108 | −21 | 8 |
Medium Residual Strength | Strain softening | 3 | 40 | 108 | −17 | 13 |
High Residual Strength | Strain softening | 3 | 40 | 108 | −13 | 23 |
Low Residual Strength | Strain softening | 5 | 40 | 187 | −13 | 31 |
Medium Residual Strength | Strain softening | 5 | 40 | 187 | −7 | 72 |
Yielding | 5 | 40 | 187 | 0 | 187 | |
Yielding | 7 | 40 | 330 | 0 | 330 | |
Low Residual Strength | Strain softening | 7 | 40 | 330 | −6 | 138 |
Yielding | 10 | 40 | 679 | 0 | 679 |
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Crushing check
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Decrease of load bearing capacity
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Application of residual strength
2.3 Simulation Types
2.3.1 Stable Pillars
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Extension of the stress shadow related to the geometry parameters
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Pillars stresses depending on the geometry and layout
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Stresses in the abutments depending on geometry and layout
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RCF depending on geometry and layout.
2.3.2 Crush Pillars
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The extension of the stress shadow
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Influence on abutment stresses
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Stability of infrastructure
2.4 Analyses Procedure
2.4.1 Stress Analyses
2.4.2 Infrastructure Stability
3 Results
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Creation of a layout of slots and pillars, which enable to conduct the high stress mining activities in the de-stressing phase
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Acceptable stress conditions for the creation of mine infrastructure such as
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Slot raises
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Production raises
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Cross cuts
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Striking drifts
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Ore passes
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Selection of most favorable mining sequence for de-stressing and production
3.1 Comparison of Layouts
Narrow slots—narrow pillars | Narrow slots—wide pillars | Wide slots—narrow pillars | Wide slots—wide pillars | |
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Extension stress shadow | Small | Small | Large | Large |
Side abutment stresses | Low | Low | High | High |
Top abutment stresses | Low | Low | High | High |
Pillar stresses | Moderate | Low | High | Moderate |
Likelihood of pillar crushing | Moderate | Low | High | Low |
Subsequent pillar extraction | Easy | Difficult | Easy | Difficult |
Production raise stability | Bad | Bad | Good | Good |
Slot raise stability side abutment | Good | Good | Medium | Good |
Slot raise stability top abutment | Moderate | Moderate | Bad | Bad |
3.2 Pillar Crushing
3.3 Mining Sequence
4 Outcome
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The interaction between pillars and slots and the overall extent of the mining system
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The influence of the layout in the de-stressing phase on the stress situation and stability of infrastructure (slot raises, production raises)
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The influence of the mining sequence in the de-stressing phase on the stress situation and stability of infrastructure (slot raises, production raises)
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The influence of pillar crushing on the stress situation and stability of infrastructure (slot raises, production raises)
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The influence of different pillar behavior on the stress situation and stability of infrastructure (slot raises, production raises)
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The influence of stope extraction on the stress situation and stability of infrastructure (slot raises, production raises)
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A layout with wide slots and wide pillars
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Wide slots:
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Large extension of the stress shadow
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Flexibility in positioning of production raise
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Wide pillars:
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Stability during de-stressing phase due to high pillar strength
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A mining sequence with an inclined mining front
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A combined method for pillar de-stressing
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Active blasting of stopes, also behind pillar
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Decrease of width to height ratio results in decrease of pillar strength
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The actual behavior of massive hard rock pillars with a considerable width to height ratio
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The influence of the broken rock mass inside the stopes on the slot stability
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The impact of hangingwall caving
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Ore flow considerations for the slot design