PowerPoint: Mining induced stress
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Transcript PowerPoint: Mining induced stress
Estimating Mining
Induced Stress
Penny Stewart BEng(Mining) PhD
Estimation of Elastic Stress
All empirical design tools, across all disciplines of engineering have one
thing in common – They must be applied consistently
Now that 3D models are commonly used, it is worth checking how this
affects 2D derived mining induced stresses upon which stability charts are
based.
1980s to late 1990s, induced stresses were estimated using 2d plain-strain
charts (Stewart and Forsyth, 1995)- Kirsch equation closed form linear
elastic solution.
Charts not applicable for low aspect ratios in the database
Map3d boundary element
Most authors used 2d stress estimation methods
Need to check Map3d against 2d model
eg Phases2d
Example: South Crofty mine: Stope 320 15H
Map3d Stress Estimation
Span = 32 m
Width = 17m
Height = 75 m
Hangingwall
Stress Resolution
Grid 3
3
-0.94 MPa
Example: Stope 320 15H
Phases 2d Stress Estimation
3
-3.2 MPa
3
Estimation of Elastic Stress II
2d Phases hybrid boundary element/finite element estimated larger tensile
stresses than Map3d
Difference between Phases2d and Map3d could not be explained for stopes
approaching 2d geometry
ie. Aspect ratio >5
Estimation of Elastic Stresses III
Further investigation required
South Crofty case study used to compare numerical modelling
programs
High aspect ratio = 83 (strike span to width)
Theoretically, 2d should be very similar to 3d model results
Compare FLAC3D (finite element) with Map3d (boundary element)
FLAC3D Stress Estimation
F L A C 3D 2.00
S te p 3 3 7 6 M o d e l
1
4 :0
4 M on M ay
P1e:1
rsp
e ctive
13 2002
C e n te
R o ta tio
r:X :
nX: :
Y
:
7 .5 0 0 e + 0 0 1
0Y.0: 0 0
1Z.2: 5 0 e + 0 0 2
0Z.0: 0 0
D
ist:
M
ag
1 .0
00e+002
0 .0
0 .:
0
A
n
g
8 .5 4 9 e + 0 0 2
4 .7 5.:
2 2 .5 0 0
P la n e
P la n e
X
:
O rig in :
NXo: rm a l:
0Y.0: 0 0 e + 0 0 0
0Y.0: 0 0 e + 0 0 0
0Z.0: 0 0 e + 0 0 0
1Z.0: 0 0 e + 0 0 0
0 .0 0 0 e + 0 0 0
0 .0 0 0 e + 0 0 0
C ontour of
la n e :
SPGM
ax
ra d ie n t
on
0 0ne + 0 0 7
C a-4
lcu.0la0tio
-3
3 .5.5000000ee++000077
-3
3 .0.0000000ee++000077
-2
2 .5.5000000ee++000077
-2
2 .0.0000000ee++000077
-1
1 .5.5000000ee++000077
-1
1 .0.0000000ee++000077
-5
5 .0.0000000ee++000066
.0000000ee++000000
00.0
.0000000ee++000066
55.0
.0000000ee++000077
11.0
In1 te
.2rva
0 0 0l e=+ 0 0 7
5 .0 e + 0 0 6
JK M R
C
to
to
to
to
to
to
to
to
to
to
to
-
Stope
3=-1.99 MPa
3=-7.59 MPa
Comparison of Stress Estimation Method:
South Crofty
Stress Estimation
Method
Minimum Tangential
Stress (MPa)
2d Plain-strain
-13.8
Map3d
-2.4
2d Phases
-7.8
FLAC3D
-2.0
2d FLAC
-3.9
Some difference
between FLAC3D
and FLAC
Comparison of Stress Estimation Methods
@ Bottom of Stope
Stress Estimation
Method
Minimum Tangential
Stress (Mpa)
2d Plain-strain
-
Map3d
- 5.0
2d Phases
-13.5
FLAC3d
-7.6
2d FLAC
-7.6
Bottom of stope
less sensitive to
element size
Conclusions: Comparison of Stress
Estimation Methods
FLAC3d, 2d FLAC and Map3d produce similar
values
Map3d stress estimates of induced stresses will be
used, not Phases2d
Further investigation is required to explain why
Phases2d is predicting larger tensile stresses than
Map3d, FLAC3d and 2d FLAC
Comparison
of codes