Upload
drdave
View
1.502
Download
2
Tags:
Embed Size (px)
DESCRIPTION
My presentation at the Round Table discussion at the 10th ISL, Xian,
Citation preview
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Strength criteria and design approaches for difficult soils and rocks
Slow moving rock slides
David PetleyDurham University, United Kingdom
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Fatal landslide distribution 2005Fatal landslide distribution 2005
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Cumulative landslide fatalities since Sept 2002Cumulative landslide fatalities since Sept 2002
2003 2004 2005 2006 2007 20082003 2004 2005 2006 2007 2008
??
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Flims, SwitzerlandFlims, Switzerland
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
• When and why do large, creeping rockslides transition into sudden failure?
• What geotechnical and geometrical parameters do we need to collect to allow behaviour to be forecast?
• Does a standard factor of safety approach apply in this case?
• If not, what does?
Key issuesKey issues
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
• Seismic events
• Intense rainstorms
• Debuttressing
• Nothing?
What triggers sudden large rock slope failure?What triggers sudden large rock slope failure?
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Three key states:-1.Movement on fully formed shear surface(s)
at residual strength• Rate of movement determined by stress
state
2.Movement associated with the ongoing formation of critical shear surface (progressive failure)• Rate of movement determined by stress
state and state of shear surface development
3.(Rheological) creep• Rate of movement determined by stress
state
The mechanical state of slow moving rockslidesThe mechanical state of slow moving rockslides
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Two key issues:-• Type of movement• Geometry
Most difficult issue is differentiating between creep and progressive failure
Potential for transition to catastrophic collapse
Landslide managementLandslide management
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Bjerrum (1967) model (ASCE) of progressive Bjerrum (1967) model (ASCE) of progressive failurefailure
• Based upon propagation of the shear surface through the slope
• Locally, the shear stress exceeds shear strength, which allows crack growth
• Slope progressively weakens to failure
Peak strengthPeak strength
Residual strengthResidual strength
Rupture surface Rupture surface growthgrowth
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Time to failure is inversely related to slope Time to failure is inversely related to slope angle in progressively failing rock slopesangle in progressively failing rock slopes
Scatter Scatter due to due to lithology lithology and size?and size?
After Kodera After Kodera et al.et al. (2005) with additional data (2005) with additional data
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Rockfall activity also increases prior to collapseRockfall activity also increases prior to collapseRosser Rosser et al.et al. 2007: 2007: Journal of Geophysical Research Journal of Geophysical Research and this conferenceand this conference
Volume of final failure (mVolume of final failure (m33))
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
0
0.05
0.1
0.15
0.2
0.25
0 20 40 60 80
Time (days)
Vel
ocity
-1 (
days
mm
-1)
Tertiary phase of progressive failureTertiary phase of progressive failure
Peak strengthPeak strength
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
Can occur if:• Global shear stress >
residual strength• Local shear stress >
peak strength
Time depends on size and stress state
Is safe design approach to use residual strength?
Progressive failureProgressive failure
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
An indication that progressive failure could An indication that progressive failure could occuroccur
Main, I.G. 2000. A damage mechanics model for power-law creep and earthquake aftershock Main, I.G. 2000. A damage mechanics model for power-law creep and earthquake aftershock and foreshock sequences. and foreshock sequences. Geophys. J. IntGeophys. J. Int. 142, 151–161. 142, 151–161
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80Time (days)
Dis
pla
cem
ent
(mm
)
Primarycreep (?)
Secondarycreep
Tertiarycreep
Landslide movement record: New Tredegar, Landslide movement record: New Tredegar, 19301930
Data from Jon Carey, Durham University and Halcrow LtdData from Jon Carey, Durham University and Halcrow Ltd
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
0
20
40
60
80
100
120
140
160
180
200
200 250 300 350 400 450Time (min)
Eff
ectiv
e no
rmal
str
ess
(kP
a)
0
2
4
6
8
10
12
Hor
izon
tal s
trai
n (%
)
BPS testing of BPS testing of Tertiary slate from JapanTertiary slate from Japan
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
BPS resultBPS result
0
50
100
150
200
250
250 300 350 400 450
Time (mins)
1/st
rain
ra
te (
min
s/m
m)
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Nor
mal
ise
d sa
mpl
e vo
lum
e
Displacement dataVolume change data
DilationDilation
∂
http: daveslandslideblog.blogspot.comhttp: daveslandslideblog.blogspot.com
• State of development of the sliding surface
• Properties of the materials• State of stress
– Global factor of safety – Local stress at crack tip
• Geometry
Presentation available for download Presentation available for download at:at:
http: http: daveslandslideblog.blogspot.comdaveslandslideblog.blogspot.com
Key issues highlightedKey issues highlighted