1
Rock Mechanics Modelling
and Engineering Design
John A Hudson
Lecture 8
F1
F2
F3
Fn
Fractures
Intact rock
Boundary
conditions
Excavation
Water flow
How do we model loading a rock mass on the surface or
excavating inside a rock mass?
2
We will construct a diagram/flowchart based on these four
methods, classified according to their complexity.
3
And we will think about two levels:
1:1 mappingthe problem is modelled directly; and
not 1:1 mappingthe problem is not modelled directly.
Use of
pre-existing
standard
methods
Precedent type
analyses and
modifications
Method A
Li S.H., Wu X.Y., & Ma F.S.
(1998) IJRMMS. Application of
Precedent Type Analysis (PTA)
in the Construction of Ertan
Hydro-Electric Station, China.
‘Simple’
4
Analytical
methods,
stress-based
e.g. the Kirsch
solution
Rock mass
classification,
RMR, Q, GSI
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Method B
Nick Barton:
“We have to damp down
the mechanisms in order to
make the model work”
Low to
medium
complexity
5
v
h
a
r
6
Why we need rock
mass classification
Foundation
Basic
numerical
methods,
FEM, BEM,
DEM, hybrid
Basic systems
approaches,
databases,
expert systems
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Method C
Medium to
high
complexity
7
Extended
numerical
methods,
e.g. coupled
THMC
Fully
integrated
systems
approaches,
internet-based
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Method D
e.g. DECOVALEX research
programmes for radioactive
waste disposal
-with the long term aim of
producing fully-coupled
thermo-hydro-mechanical-
chemical numerical models
Next slide
Complicated
8
9
Method D
Level 2
possibilities
Use of
pre-existing
standard
methods
Analytical
methods,
stress-based
Basic
numerical
methods, FEM,
BEM, DEM,
hybrid
Extended
numerical
methods,
fully-coupled
models
Precedent type
analyses and
modifications
Rock mass
classification,
RMR, Q, GSI
Database
expert
systems, &
other systems
approaches
Integrated
systems
approaches,
internet-based
Objective
Construction
Site
Invest-
igation
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Design based on forward analysis Design based on back analysis
Method A Method B Method C Method D
Leading to this composite flowchart
10
The content of the
following slides in this
lecture can be found in
the 2011 book by Feng
and Hudson
11
12
13
Some of the questions that stimulated us as the work by
the ISRM Commission developed…
14
The Figure 2.1 flowchart summarising the modelling approaches
15
Applications
17
Design of a hydroelectric
powerhouse cavern:
Shuibuya project in China
Initial design
20
Initial design
21
Cracking of shotcrete
Spalling
Maximum principal
stress
Maximum principal
stress
Location of typical local failures (at Jinping II
powerhouse after Excavation Stage IV) 22
Final design
23
What information do we need to use these eight approaches?
Use of
pre-existing
standard
methods
Analytical
methods,
stress-based
Basic
numerical
methods, FEM,
BEM, DEM,
hybrid
Extended
numerical
methods,
fully-coupled
models
Precedent type
analyses and
modifications
Rock mass
classification,
RMR, Q, GSI
Database
expert
systems, &
other systems
approaches
Integrated
systems
approaches,
internet-based
Objective
Construction
Site
Invest-
igation
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Design based on forward analysis Design based on back analysis
Method A Method B Method C Method D
25
Principles for modelling
26
Use of
pre-existing
standard
methods
Analytical
methods,
stress-based
Basic
numerical
methods, FEM,
BEM, DEM,
hybrid
Extended
numerical
methods,
fully-coupled
models
Precedent type
analyses and
modifications
Rock mass
classification,
RMR, Q, GSI
Database
expert
systems, &
other systems
approaches
Integrated
systems
approaches,
internet-based
Objective
Construction
Site
Invest-
igation
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Design based on forward analysis Design based on back analysis
Method A Method B Method C Method D
27
Use of
pre-existing
standard
methods
Analytical
methods,
stress-based
Basic
numerical
methods, FEM,
BEM, DEM,
hybrid
Extended
numerical
methods,
fully-coupled
models
Precedent type
analyses and
modifications
Rock mass
classification,
RMR, Q, GSI
Database
expert
systems, &
other systems
approaches
Integrated
systems
approaches,
internet-based
Objective
Construction
Site
Invest-
igation
Level 1
1:1 mapping
Level 2
Not 1:1 mapping
Design based on forward analysis Design based on back analysis
Method A Method B Method C Method D
The Fig.
3.12
design
flowchart
30
Principles for numerical code implementation
31
Laxiwa project
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33
The Yellow River, China
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35
36
37
Computer models and
choice of cavern orientation
38
Main powerhouse
Transformer
chamber
A1-7
A2-7
A2-5
P1
P3 P4
ZBA-5 ZBA-2
A1 A2
A4
A5
ZBA
A4-7
A5-1
A5-6
P2
Monitoring points chosen
39
Questions to be asked
40
End of Lecture 8
41
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