Proposed Design Methodology for shotcrete

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Proposed Design Methodology for shotcrete

• W.C Joughin, G.C. Howell, A.R. Leach J. Thompson

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Research Workshop Team

• William Joughin
• Graham Howell
• Tony Leach
• Jody Thompson
• Kevin Le Bron
• Karl Akermann (AngloPlatinum), Lars Hage (BASF),
  Alan Naismith, Julian Venter, Dave Ortlepp

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Design Process

• Determination of Shotcrete Requirements
• Excavation requirements
• Shotcrete function/purpose
• Is it required?

• Determination of rock mass and loading
  conditions
• Rock mass classification
• Stress modelling

• Determination of Shotcrete Demand
• Deadweight loading
• Quasi-static loading
• Dynamic loading

• Determination of Shotcrete Capacity
• Peak/Residual capacity
• Energy absorption
• Standard tests
• Fibre content, mesh characteristics

Determination of safety factor
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Rock mass conditions

• Q/GSI
• Stress modelling

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Shotcrete requirements(Excavation requirements)

• Importance of excavation (access/production)
• Exposure of personnel
• Life of excavation
• Functional dimensions of excavation
• Maintenance and rehabilitation (redundancy)

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Shotcrete requirements(Shotcrete
function/purpose)

• Structural support (Not covered)
• Fabric between tendons to contain
  jointed/fractured rock
• To prevent spalling/strainbursting near face

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Shotcrete requirements(is it required?)

• Observations of block size and stress damage
• Keyblock analysis (eg Jblock) (joint controlled)
• Stress damage (RCFgt0.7, ?1/?c ratio)
• Empirical charts (joint controlled SRF)

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Shotcrete requirements
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Shotcrete requirements
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Shotcrete Demand

• Deadweight
• Quasi-static
• Dynamic

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Shotcrete Demand (deadweight)

• Roof prism (Barret McCreath)
• Sidewall prism slides
• Conservative estimate

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Shotcrete Demand (Deadweight)
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Shotcrete Demand (quasi-static)

• Assumption Rock mass will continue to deform
  under quasi-static loading. Support pressures
  provided by shotcrete are inadequate to prevent
  deformation.
• Objective is to survive the deformation and
  maintain the functions of containing the
  fractured rock mass
• If the moment demand exceeds the peak moment
  capacity, the shotcrete will enter the residual
  state, providing it is reinforced.

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Shotcrete Demand (quasi-static)(Displacement)

• Displacement monitoring (extensometers)
• Maximum displacement from Udec GRC modelling

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Displacement from modelling
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Shotcrete Demand (quasi-static)(Displacement)
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Shotcrete Demand (quasi-static)
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Shotcrete Demand (Dynamic)

• Roof Prism (Barret McCreath

• Sidewall Kinetic Energy
• Roof Kinetic and potential energy

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Shotcrete Demand (Dynamic)
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Shotcrete Demand (Dynamic)
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Shotcrete Capacity

• Peak/residual strength
• Energy Absorption
• Standard tests (RDP/ASTMC1550, EFNARC)
• Fibre content
• Mesh area

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Shotcrete Capacity (RDP)
Peak load
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Shotcrete Capacity (RDP)
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Shotcrete Capacity (RDP)
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Shotcrete Capacity (RDP)
Generic
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Shotcrete Capacity (on wall)
75mm thick, 1m tendon spacing
8.66 x
1.33 x
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Shotcrete Capacity (on wall)
75mm thick, 1m tendon spacing
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Shotcrete capacity (Dynamic)
RDP
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Factor of safety
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Outstanding work

• Large scale panel tests (Kirsten Labrum)
• UDL point load
• Thickness (50mm, 100mm, 150mm)
• Mesh fibre
• Large scale panel tests (Shotcrete working group
  Gerhard Keyter)

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Acknowledgements

• Mine Health and Safety Council (SIM040204)
• South Deep Gold Mine, Mponeng Mine, Impala 14
• BASF (Lars Hage), Mash (Hector Snashall)
• Geopractica, University of the Witwatersrand
• Seismogen (Tony Ward)
• James Dube, Hlangabeza Gumede