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 ProcessDetermination 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

•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

Rock mass conditions Q/GSI Stress

modelling

Low Stress Moderate stress High Stress DynamicLoading Condition

Mas

sive

(>70

)Jo

inte

d (4

0-70

)H

eavi

ly jo

inte

d (<

40)

Rock

Mas

s Co

nditi

on (

GSI

) Limited or no damage. Fracturing and minor spalling of rock occurs.

Intense fracturing, spalling and bulking of rock occurs.

Violent ejection of rock.

A1 A2 A3 A4

Blocks or wedges mobilize under gravity loading.

B1

Fracturing is altered by joint pattern. Blocks or wedges begin to slide.

B2

Intense fracturing and sliding along joints. Blocks or wedges slide.

B3

Violent ejection of rock.

B4

Unravelling of small blocks.

C1

Unravelling of small blocks. Failure can propagate into the rock mass if not controlled

C2 C3

Unravelling and crushing of blocks. Sliding along joints can create squeezing conditions

C4

Violent ejection of rock and unravelling

Shotcrete requirements(Excavation requirements)

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?)

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)

Roof prism (Barret & McCreath)

Sidewall prism slides Conservative estimate

0.1

1

10

100

0 1 2 3 4 5 6

md

(kN

m/m

)

Span between tendons (m)

20 kN/m3

25kN/m3

30 kN/m3

35kN/m3

40 kN/m3

Shotcrete Demand (Deadweight)

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

0.E+00

1.E+05

2.E+05

3.E+05

4.E+05

5.E+05

6.E+05

7.E+05

8.E+05

9.E+05

1.E+06

0.00 5.00 10.00 15.00 20.00 25.00 30.00

Deformation (mm)

Su

pp

ort

Pre

ssu

re (

Pa

)

300 MPa

250 MPa

200 MPa

150 MPa

Displacement from modelling

Shotcrete Demand (quasi-static)(Displacement)

Quartzite150-200MPa 200-250MPa 250-300MPa

20 48.20 Squeezing Squeezing

30 5.50 Squeezing Squeezing

40 4.50 43.00 51.00

50 8.00 25.30 35.70

60 7.50 6.70 7.80

70 4.00 5.50 5.50

80 4.00 3.50 4.00

90 2.75 1.30 4.60

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

0 1 10 100 1,000

md

(kN

m/m

)

Deflection (mm)

a=1.0m h=25mm

a=1.0m h=50mm

a=1.0m h=75mm

a=1.0m h=100mm

a=1.0m h=150mm

a=1.0m h=200mm

a=1.5m h=25mm

a=1.5m h=50mm

a=1.5m h=75mm

a=1.5m h=100mm

a=1.5m h=150mm

a=1.5m h=200mm

Square tendon spacing (a)Thickness (h)

Impala

SD site 2 initial

SD site 2 final

Mponeng

Shotcrete Demand (quasi-static)

Shotcrete Demand (Dynamic) Roof Prism (Barret &

McCreath Sidewall: Kinetic Energy Roof: Kinetic and potential

energy

0.01

0.1

1

10

100

0.5 1 1.5 2 2.5 3 3.5

Kine

tic E

nerg

y (k

J)

Span between tendons (m)

0.2 m/s

0.5 m/s

1.0 m/s

1.5 m/s

2.0 m/s

2.5 m/s

3.0 m/sSouth Deep Blast PPV

South Deep Site effect

Mponeng Max PPV

Mponeng threshold PPV

Shotcrete Demand (Dynamic)

0.1

1

10

0.5 1 1.5 2 2.5 3 3.5

Pote

ntial

Ene

rgy

(kJ)

Span between tendons (m)

Shotcrete Demand (Dynamic)

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

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40 45

Wpc

(kN

)

Deflection (mm)

Steel 40kg/m3

Steel 55kg/m3

Steel 70kg/m3

Polypropylene 1kg/m3

Polypropylene 2kg/m3

Polypropylene 3kg/m3

Polypropylene 4kg/m3

Polypropylene 5kg/m3

Polypropylene 6kg/m3

Polypropylene 7kg/m3

Polypropylene 8kg/m3

Shotcrete Capacity (RDP)

Peak load

Shotcrete Capacity (RDP)

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0 10 20 30 40 50 60

mc

(Nm

/m)

RDP Wpc (kN)

25mm

50mm

100mm

150mm

200mm

Thickness (h)

70kg/m3 steel fibre mix40kg/m3 steel fibre mix

55kg/m3 steel fibre mix1-8kg/m3 poly fibre mixes

Impala

South Deep site 2

Mponeng

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40 45

Wpc

(kN

)

Deflection (mm)

Steel 40kg/m3

Steel 55kg/m3

Steel 70kg/m3

Polypropylene 1kg/m3

Polypropylene 2kg/m3

Polypropylene 3kg/m3

Polypropylene 4kg/m3

Polypropylene 5kg/m3

Polypropylene 6kg/m3

Polypropylene 7kg/m3

Polypropylene 8kg/m3

Shotcrete Capacity (RDP)

Shotcrete Capacity (RDP)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.000 0.020 0.040 0.060 0.080 0.100 0.120

mpc

(kN

m/m

)

(radians)

Steel 40kg/m3

Steel 55kg/m3

Steel 70kg/m3

Polypropylene 1kg/m3

Polypropylene 2kg/m3

Polypropylene 3kg/m3

Polypropylene 4kg/m3

Polypropylene 5kg/m3

Polypropylene 6kg/m3

Polypropylene 7kg/m3

Polypropylene 8kg/m3

Genericδ

P (Load)Lever Arm = L/2

θ

0

50

100

150

200

250

300

350

400

0.00 10.00 20.00 30.00 40.00 50.00 60.00

Wc(

kN)

Deflection (mm)

Steel 40kg/m3

Steel 55kg/m3

Steel 70kg/m3

Shotcrete Capacity (on wall)

75mm thick, 1m tendon spacing8.66 x

1.33 x

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0.00 10.00 20.00 30.00 40.00 50.00 60.00

EAc(

J)

Deflection (mm)

Steel 40kg/m3

Steel 55kg/m3

Steel 70kg/m3

40 kg/m3 Panel

55 kg/m3 panel

70 kg/m3 panel

Shotcrete Capacity (on wall)75mm thick, 1m tendon spacing

0.1

1

10

100

0 0.2 0.4 0.6 0.8 1 1.2

EAc(k

J)

RDP EApc (kJ)

25mm

50mm

100mm

150mm

200mm

Thickness (h)

70kg/m3 steel fibre mix40kg/m3 steel fibre mix

55kg/m3 steel fibre mix

Impala

South Deep site 2

Mponeng

Shotcrete capacity (Dynamic)RDP

Factor of safety

Loading South Deep Site

2

South Deep Site

2

Mponeng 116 level

Impala

Deadweight 2.4 2.4 72.1 4.6Quasi-static 1.0 0.1 9.3 2.6Dynamic Max 1.1 32.6Dynamic (3m/s) 0.1 0.9 0.08

Outstanding work Large scale panel tests (Kirsten & Labrum)

UDL & point loadThickness (50mm, 100mm, 150mm)Mesh & fibre

Large scale panel tests (Shotcrete working group – Gerhard Keyter)

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