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100+ Free Certificate in Strata Control — Metalliferous Exam Practice Questions
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Sample Certificate in Strata Control — Metalliferous Exam Practice Questions
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1In deep South African tabular gold mines subject to rockburst conditions, what is the primary function of a Rapid Yielding Hydraulic Prop (RYHP)?
A.To maintain a rigid, unyielding force until the surrounding rock mass fails completely
B.To yield at a controlled force under high-velocity dynamic convergence while maintaining support resistance
C.To provide temporary support during drilling only and be removed prior to blasting
D.To serve as a passive timber replacement without any internal pressure relief mechanism
Explanation: Rapid Yielding Hydraulic Props (RYHPs) are designed with a high-flow pressure relief valve set to yield at a specified force (typically 200 kN or 400 kN) when subjected to rapid closure velocities up to 1 to 3 m/s during seismic events. This controlled yielding absorbs dynamic energy while keeping the hangingwall intact.
2A stope hangingwall has an expected potential unstable fallout height of 1.2 m. Assuming a rock density of 2700 kg/m³ and gravitational acceleration g = 9.81 m/s², calculate the required minimum Support Resistance (SR) in kPa to stabilize this deadweight load.
A.31.8 kPa
B.42.5 kPa
C.25.4 kPa
D.18.2 kPa
Explanation: Support Resistance SR is calculated using SR = rho * g * h. Here, SR = 2700 kg/m³ * 9.81 m/s² * 1.2 m = 31,784.4 Pa ≈ 31.8 kPa.
3A line of 200 kN RYHPs is installed in a stope with a prop spacing of 1.5 m along strike and 1.2 m along dip. Calculate the support resistance provided by this prop layout.
A.111.1 kPa
B.166.7 kPa
C.88.9 kPa
D.200.0 kPa
Explanation: Tributary area per prop A = 1.5 m * 1.2 m = 1.8 m². Support Resistance SR = Capacity / Area = 200 kN / 1.8 m² = 111.11 kN/m² = 111.1 kPa.
4Which characteristic makes stiff composite packs preferable to traditional timber mat packs in deep tabular stopes with high convergence rates?
A.Composite packs have higher initial stiffness and yield capability, reducing initial stope closure and bed separation
B.Composite packs are completely rigid and do not compress under stope closure
C.Timber mat packs have superior initial stiffness compared to concrete-timber composite packs
D.Composite packs are significantly lighter and easier to assemble manually than pure timber packs
Explanation: Composite packs (combining concrete blocks with timber units) offer a much higher initial load-deformation modulus (stiffness) than pure timber packs, preventing early bed separation in the immediate hangingwall while still providing yielding capacity.
5What is a major strata control benefit of placing cemented classified tailings backfill in deep narrow-vein tabular stopes?
A.It reduces total regional stope closure and Energy Release Rate (ERR), lowering overall rockburst risk
B.It completely eliminates the need for any face area support or tendon installation
C.It increases the stress concentration at the immediate stope face area to enhance rock breaking
D.It acts as a rigid non-compressible pillar with zero volume change under deep overburden pressure
Explanation: Backfill fills the mined-out void (gaf), restricting macro-closure of the hangingwall and footwall. This significantly reduces the regional Energy Release Rate (ERR) and peak abutment stresses ahead of the face.
6A seismic event causes an ejection velocity v = 2.5 m/s of a 1.0 m thick hangingwall block (density = 2800 kg/m³). Calculate the dynamic kinetic energy per square metre that the support system must absorb.
A.8.75 kJ/m²
B.3.50 kJ/m²
C.17.50 kJ/m²
D.12.25 kJ/m²
Explanation: Mass per unit area m = rho * thickness = 2800 kg/m³ * 1.0 m = 2800 kg/m². Kinetic energy per unit area E_k = 0.5 * m * v² = 0.5 * 2800 * (2.5)² = 0.5 * 2800 * 6.25 = 8750 J/m² = 8.75 kJ/m².
7Under South African Mine Health and Safety Act regulations and FOG COP guidelines, why is the maximum allowable distance between the blast face and the first line of support strictly regulated?
A.The face area experiences the highest stress concentration and key block unravelling, representing the greatest FOG risk zone
B.To allow clearance for scraper scoops to operate without bumping into timber props
C.To ensure blast vibrations do not damage the hydraulic seals of RYHPs
D.To prevent backfill from spilling into the active face track
Explanation: The immediate stope face is the active working area where miners spend significant time and where stress fracturing and key block unravelling are most acute. Minimizing unsupported spans reduces fall-of-ground fatalities.
8What is the primary function of installing a hydraulic prestressing pot (e.g. Jackpack) on top of a timber or composite pack in a stope?
A.To immediately actively load the pack against the hangingwall, taking up blast-shock and preventing key block dislocation
B.To permanently lock the pack height so that no closure can occur
C.To pump cement slurry into the pack core to convert it into a solid pillar
D.To act as a remote blast indicator that explodes under dynamic compression
Explanation: Prestressing units inflate upon installation (using water or grout) to push the pack tightly against the hangingwall, providing immediate active support force (typically 50-150 kN) before stope closure begins.
9Calculate the total potential energy per unit area E_total (in kJ/m²) that a yielding support must absorb when arresting a 1.5 m thick block (density 2700 kg/m³) ejected at 2.0 m/s, assuming a yield displacement distance d = 0.2 m under gravity g = 9.81 m/s².
A.16.03 kJ/m²
B.8.10 kJ/m²
C.24.15 kJ/m²
D.11.89 kJ/m²
Explanation: Mass per m² m = 2700 * 1.5 = 4050 kg/m². E_kinetic = 0.5 * 4050 * (2.0)² = 8100 J/m² = 8.10 kJ/m². E_potential = m * g * d = 4050 * 9.81 * 0.2 = 7946.1 J/m² ≈ 7.95 kJ/m². E_total = 8.10 + 7.95 = 16.05 kJ/m² ≈ 16.03 kJ/m².
10In narrow tabular stopes of the Witwatersrand basin, why are full-column grouted flexible tendons (e.g., rope cables or steel rebars) installed in the hangingwall?
A.To pin thin, weak hangingwall laminations together (beam building) and retain beam integrity above the stope
B.To lower the stress state in the footwall so that footwall lifting is completely stopped
C.To substitute for all timber packs and allow pack-free stopes across all depths
D.To pull down loose blocks prior to entry of mining personnel
Explanation: Full-column grouted tendons bind individual rock strata/laminations together, creating a thicker composite beam with higher flexural rigidity and shear strength to resist bed separation.
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