1

Stope Back DesignCase History

• Wedge failure problems had beenencountered in the past.

• Increased cable bolting was applied toimprove stability

Back/HW Support?

2

Rock Mass Properties

‐ 3 joint sets were present

‐ Joint set A was at a 30 degree dip

‐ Rock UCS = 100 MPa

‐ Induced stress = 50 MPa

‐ Joint set A:   JRC10 = 14    1m Amp = .7cm

‐ Joint surfaces cannot be scratched with a fingernail

‐ RQD = 100%

Factor AStrength/stress

Uniaxial Compressive Strength, UCSMax. Induced Compressive Stress, max.

0 2 4 6 8 10 12

0

0.2

0.4

0.6

0.8

1

Ratio:

Roc

k S

tres

s fa

cto r

A

Max.

Stope Face

Obtain max. from 2D or 3Dnumerical stress modelling

3

0 10 20 30 40 50 60 70 80 900

0.2

0.4

0.6

0.8

1.0

Ture Angle Between Face and Joint(Angle Between Poles)

Join

t Orie

nta t

ion

Fac

tor

B

Factor B

True Angle Between Face and Joint

0 10 20 30 40 50 60 70 80 900

2

4

6

8

10

Dip of Stope Face

Gra

vity

Adj

ustm

e nt F

acto

r, C

C=8-6cos(Dip)

Factor CGravty Fall &Slabbing

Face Dip

Sto

pe

4

Stope Geometry

• Stope is 14m wide by approx. 53m long.

• Cable bolting was done with 3 passes

• Design a stable cable support

5

Design Parameters

• Jr = 1.5 3 joint sets & 100% RQD

• Ja = 1.0

• Q’ = 17

• A = 0.1 B = .2 C = 2.0

• N’ = 0.8

• H.R. = 5.5m

6

100/9/5.5=2

RQD/Jn/HR = 2.0

7

Sp

an (

m)

Pote

ntia

l U

nsta

ble

Zon

e

Stable Zone

RMR

Unstable Zone

45

40

35

30

Unstable Potential Stable

20

10

15

0

5

Stable

25

0 10 20 30 40 50 60 70 80 90 100

Span Design (Wang et al., 2000)

2 Months Later

8

9