Transcript No Slide Title

Proposed Design
Methodology for shotcrete
W.C Joughin, G.C. Howell, A.R.
Leach & J. Thompson
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
Design Process
Determination of rock
mass and loading
conditions
•Rock mass classification
•Stress modelling
Determination of Shotcrete
Requirements
•Excavation requirements
•Shotcrete function/purpose
•Is it required?
Determination of
Shotcrete Demand
Determination of
Shotcrete Capacity
•Peak/Residual capacity
•Energy absorption
•Standard tests
•Fibre content, mesh
characteristics
•Deadweight loading
•Quasi-static loading
•Dynamic loading
Determination
of safety factor
Rock mass conditions
 Q/GSI
 Stress
modelling
Loading Condition
Low Stress
Massive (>70)
Jointed (40-70)
Heavily jointed (<40)
Rock Mass Condition (GSI)
A1
Moderate stress
High Stress
A2
A3
Dynamic
A4
Limited or no damage.
Fracturing and minor spalling of Intense fracturing, spalling and
rock occurs.
bulking of rock occurs.
Violent ejection of rock.
B1
B2
B4
B3
Blocks or wedges mobilize under Fracturing is altered by joint
Intense fracturing and sliding
gravity loading.
pattern. Blocks or wedges begin along joints. Blocks or wedges
to slide.
slide.
Violent ejection of rock.
C1
C2
C3
C4
Unravelling of small blocks.
Unravelling of small blocks.
Failure can propagate into the
rock mass if not controlled
Unravelling and crushing of
blocks. Sliding along joints can
create squeezing conditions
Violent ejection of rock and
unravelling
Shotcrete requirements
(Excavation requirements)
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Importance of excavation (access/production)
Exposure of personnel
Life of excavation
Functional dimensions of excavation
Maintenance and rehabilitation (redundancy)
Shotcrete requirements
(Shotcrete function/purpose)
 Structural support (Not covered)
 Fabric between tendons to contain
jointed/fractured rock
 To prevent spalling/strainbursting near face
Shotcrete requirements
(is it required?)
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Observations of block size and stress damage
Keyblock analysis (eg Jblock) (joint controlled)
Stress damage (RCF>0.7, 1/c ratio)
Empirical charts (joint controlled + SRF)
Shotcrete requirements
Shotcrete requirements
Shotcrete Demand
 Deadweight
 Quasi-static
 Dynamic
Shotcrete Demand
(deadweight)
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Roof prism (Barret &
McCreath)
Sidewall prism slides
Conservative estimate
md (kNm/m)
100
Shotcrete Demand
(Deadweight)
10
20 kN/m3
25kN/m3
30 kN/m3
1
35kN/m3
40 kN/m3
0.1
0
1
2
3
4
5
Span between tendons (m)
6
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.
Shotcrete Demand (quasi-static)
(Displacement)
 Displacement monitoring (extensometers)
 Maximum displacement from Udec GRC
modelling
1.E+06
Displacement from modelling
9.E+05
Support Pressure (Pa)
8.E+05
7.E+05
6.E+05
5.E+05
4.E+05
300 MPa
3.E+05
250 MPa
2.E+05
1.E+05
0.E+00
0.00
200 MPa
150 MPa
5.00
10.00
15.00
Deformation (mm)
20.00
25.00
30.00
Shotcrete Demand (quasi-static)
(Displacement)
Quartzite
150-200MPa 200-250MPa 250-300MPa
20
30
40
50
60
70
80
90
48.20
5.50
4.50
8.00
7.50
4.00
4.00
2.75
Squeezing
Squeezing
43.00
25.30
6.70
5.50
3.50
1.30
Squeezing
Squeezing
51.00
35.70
7.80
5.50
4.00
4.60
1.E+05
Shotcrete Demand (quasi-static)
Square tendon spacing (a)
Thickness (h)
1.E+04
a=1.0m h=25mm
1.E+03
a=1.0m h=50mm
md (kNm/m)
a=1.0m h=75mm
a=1.0m h=100mm
1.E+02
a=1.0m h=150mm
a=1.0m h=200mm
SD site 2 final
1.E+01
a=1.5m h=25mm
Mponeng
a=1.5m h=50mm
SD site 2 initial
1.E+00
a=1.5m h=75mm
Impala
a=1.5m h=100mm
1.E-01
a=1.5m h=150mm
a=1.5m h=200mm
1.E-02
0
1
10
Deflection (mm)
100
1,000
Shotcrete Demand (Dynamic)
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Roof Prism (Barret &
McCreath
Sidewall: Kinetic Energy
Roof: Kinetic and potential
energy
Shotcrete Demand (Dynamic)
Kinetic Energy (kJ)
100
0.2 m/s
10
0.5 m/s
1.0 m/s
1
0.1
South Deep Site effect
1.5 m/s
Mponeng Max PPV
2.0 m/s
Mponeng threshold PPV
South Deep Blast PPV
2.5 m/s
3.0 m/s
0.01
0.5
1
1.5
2
2.5
Span between tendons (m)
3
3.5
10
Potential Energy (kJ)
Shotcrete Demand (Dynamic)
1
0.1
0.5
1
1.5
2
2.5
Span between tendons (m)
3
3.5
Shotcrete Capacity
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Peak/residual strength
Energy Absorption
Standard tests (RDP/ASTMC1550, EFNARC)
Fibre content
Mesh area
Shotcrete Capacity (RDP)
60
50
Peak load
Steel 40kg/m3
Steel 55kg/m3
40
Wpc(kN)
Steel 70kg/m3
Polypropylene 1kg/m3
30
Polypropylene 2kg/m3
Polypropylene 3kg/m3
Polypropylene 4kg/m3
20
Polypropylene 5kg/m3
Polypropylene 6kg/m3
10
Polypropylene 7kg/m3
Polypropylene 8kg/m3
0
0
5
10
15
20
25
Deflection (mm)
30
35
40
45
Shotcrete Capacity (RDP)
1.E+03
55kg/m3 steel fibre mix
1-8kg/m3 poly fibre mixes
40kg/m3 steel fibre mix
mc (Nm/m)
1.E+02
70kg/m3 steel fibre mix
Thickness (h)
25mm
Mponeng
1.E+01
50mm
100mm
150mm
South Deep site 2
1.E+00
200mm
Impala
1.E-01
0
10
20
30
RDP Wpc (kN)
40
50
60
Shotcrete Capacity (RDP)
60
50
Steel 40kg/m3
Steel 55kg/m3
40
Wpc(kN)
Steel 70kg/m3
Polypropylene 1kg/m3
30
Polypropylene 2kg/m3
Polypropylene 3kg/m3
Polypropylene 4kg/m3
20
Polypropylene 5kg/m3
Polypropylene 6kg/m3
10
Polypropylene 7kg/m3
Polypropylene 8kg/m3
0
0
5
10
15
20
25
Deflection (mm)
30
35
40
45
Shotcrete Capacity (RDP)
12.00
Lever Arm = L/2
Generic
P (Load)
θ
10.00
δ
Steel 40kg/m3
Steel 55kg/m3
mpc (kNm/m)
8.00
Steel 70kg/m3
Polypropylene 1kg/m3
6.00
Polypropylene 2kg/m3
Polypropylene 3kg/m3
Polypropylene 4kg/m3
4.00
Polypropylene 5kg/m3
Polypropylene 6kg/m3
2.00
Polypropylene 7kg/m3
Polypropylene 8kg/m3
0.00
0.000
0.020
0.040
0.060
 (radians)
0.080
0.100
0.120
Shotcrete Capacity (on wall)
400
8.66 x
75mm thick, 1m tendon spacing
350
300
Wc(kN)
250
200
Steel 40kg/m3
Steel 55kg/m3
150
Steel 70kg/m3
100
50
0
0.00
10.00
1.33 x
20.00
30.00
Deflection (mm)
40.00
50.00
60.00
Shotcrete Capacity (on wall)
9000
8000
75mm thick, 1m tendon spacing
7000
EAc(J)
6000
Steel 40kg/m3
5000
Steel 55kg/m3
Steel 70kg/m3
4000
40 kg/m3 Panel
3000
55 kg/m3 panel
70 kg/m3 panel
2000
1000
0
0.00
10.00
20.00
30.00
Deflection (mm)
40.00
50.00
60.00
Shotcrete capacity (Dynamic)
100
RDP
55kg/m3 steel fibre mix
40kg/m3 steel fibre mix
10
70kg/m3 steel fibre mix
EAc (kJ)
Mponeng
Thickness (h)
25mm
50mm
South Deep site 2
100mm
150mm
1
200mm
Impala
0.1
0
0.2
0.4
0.6
RDP EApc (kJ)
0.8
1
1.2
Factor of safety
Loading
Deadweight
Quasi-static
Dynamic Max
Dynamic (3m/s)
South
South
Mponeng
Deep Site Deep Site 116 level
2
2
2.4
2.4
72.1
1.0
0.1
9.3
1.1
32.6
0.1
0.9
Impala
4.6
2.6
0.08
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)
Acknowledgements
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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