Landslide Runout Analysis using 2d-DMM, 3d-DMM and LS-DYNA
for
Benchmarking Exercise for Landslide Runout Analysis
RAYMOND LAW AND RAYMOND KOO, GEO, CEDD, HKSARG
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ContentsIntroduction
Observations:Case A1
Case B1
Case C1
Case C2
Case D1
Case D2
Conclusions
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IntroductionThe six benchmarking cases are attempted using three numerical tools
Numerical tool 1 – 2d-DMM
Principles:
Shallow water approximation
Curvilinear flow path with prescribed cross section
Friction and Voellmy rheology
Case analysed using 2d-DMM: B1
2d-DMM
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IntroductionNumerical tool 2 – 3d-DMM
Principles:
Smoothed Particle Hydrodynamics
Shallow water approximation
Three dimensional flow path
Friction and Voellmy rheology
Case analysed using 3d-DMM: A1, C1, C2, D1, D2
3d-DMM
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IntroductionNumerical tool 3 – LS-DYNA
Principles:
Arbitrary Lagrangian-Eulerian (ALE) description of finite-element method
Discretised into an array of uniform hexahedral elements
Continuum model with friction and Voellmy rheology
Case analysed using 3d-DMM: C1
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Observation – Case A13d-DMM input parameters:
Internal friction angle = 23 (given)
Interface friction angle = 11 (back-
analysed)
Smoothing coefficient = 4
Particle volume = 8000 m3
Number of particle = 4400
Time step interval = 0.05 s
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Observation – Case A1 With interface friction angle = 11, the
deposition area match with the trimline in general
Flow velocity as high of 50 m/s
A small portion of the landslide go beyond the trimline due to the topography at source location
Spreading of the landslide debris smaller than that of the trimline.
Time=30s
A
21
A
Local ridge line
21
Source debris
Section A-A
Time=120sUpslope motion required to reach this region
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Observation – Case B12d-DMM input parameters:
Interface friction angle = 1
Turbulence coefficient: 125 ms-2
Source volume = 160,000 m3
Time step interval = 0.01 s
3d-DMM was attempted but was found to
be computationally impracticable.
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Observation – Case B1 Extremely low interface friction angle (i.e.
1) required to match both velocity and runout match with the field observation
When interface friction angle beyond certain threshold (i.e. 7), the runout does not change with turbulence coefficient
Very watery landslide event!
1 4 7
1 / 250
1 / 125
1 / 75
101%
90%
107% 93%
80%
70% 27%
27%
27%
Interface friction angle (0)
1 /
tu
rbu
len
t co
effic
ient (
s 2 / m
)
Increasing runout
distance
Computed runout distance
Measured runout distance𝑋 100%
Landslide debris stopped at around
3 km from the source location
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Observation – Case C13d-DMM input parameters:
Internal frictional angle = 30 (assumed)
Interface friction angle = 8 (given)
Turbulence coefficient: 500 ms-2 (given)
Particle volume = 0.52 m3
Number of particle = 5,000
LS-DYNA input parameters:
Internal frictional angle = 15 (back-calculated)
Interface friction angle = 8 (given)
Turbulence coefficient: 500 ms-2 (given)
Source location
Disruption to traffic
A
B
C
D
E
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Observation – Case C1
General match between the field and numerical velocities
3d-DMM and LS-DYNA yield similar results
time = 65s
Location ABC
D
E
The simulated debris reaches the Yu
Tung Road.
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Observation – Case C23d-DMM input parameters:
Internal frictional angle= 30 (assumed)
Interface friction angle:
Drainage channel = 6 (back-analysed)
Bench = 28 (back-analysed)
Turbulence coefficient=5000 m/s2 (back-
analysed)
Particle volume = 50 m3
Number of particle = 7000
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Observation – Case C2 An interesting cases - velocity have to be
high enough to choose path (1) andreach the bench.
With such velocity, debris will travelbeyond the trimline.
Two friction regions are therefore need.
Low friction for the upper drainage line
High friction to take into account the flowresistance on the bench due to vegetation time = 30 s
Landslide debris will only take
path 1 at relatively high velocity.
2
1
Point A
1
2
Deposit on the bench
Travel along the drainage line
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Observation – Case C2
General match between the field andcomputed runout distance
Spreading extent of the landslide debrissmaller than the trimline.
time = 50 s
The simulated landslide deposit does
not cover the entire trimline region.
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Observation – Case D13d-DMM input parameters:
Internal frictional angle= 30 (assumed)
Interface friction angle = 8 (given)
Turbulence coefficient = 5,000 m/s2 (given)
Particle volume = 2 m3
Number of particle = 5,000
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Observation – Case D1 Landslide debris reach the downslope
access road and residential buildings
Velocity from 7 to 9 m/s; thickness above 2 m
Mitigation measures against the landslide risk is therefore required if such landslide is realised
Locations Maximum flow thickness
(m)
Maximum flow velocity
(m/s)Point A 2.6 9.2
Point B 2.4 7.5
Point C 2.4 7.1
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Observation – Case D23d-DMM input parameters:
Internal frictional angle= 30 (assumed)
Interface friction angle = 17
Turbulence coefficient=5000 m/s2 (given)
Particle volume = 1700 m3
Number of particle = 5000
Time=0s Time=20s Time=40s
Time=60s Time=80s Time=140s
Debris thickness (m)
0
15
30
45
>60
A small portion of the source debris
travel to the other side of the ridge
1
2
Preliminary hazard zone
a)
b)
Reference Proposed Relationship H/L angle (deg.)
Scheidegger (1973) log10(H/L) = -0.15666log10V+ 0.62419 0.35 19
Li (1983) log10(H/L) = -0.1529log10V+ 0.6640 0.40 22
Corominas (1996)
all landslideslog10(H/L) = -0.085log10V- 0.047 0.23 13
Corominas (1996)
rock fallslog10(H/L) = -0.109log10V+ 0.210 0.29 16
Corominas (1996)
obstructed rock fallslog10(H/L) = -0.091log10V+ 0.231 0.40 22
Corominas (1996)
unobstructed rock fallslog10(H/L) = -0.119log10V+ 0.167 0.22 12
17Average:
Blasio (2011) 17
Observation – Case D2 A small portion of the source debris
chooses the opposite flow direction
Post landslide debris travel through the slopes to the deposition region
A preliminary hazard zone delineated based on the computed travel extent
Time=20s
A small portion of the source debris
travel to the other side of the ridge
1
2
Time=140s
Preliminary hazard zone
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Conclusions Generally satisfactory results for the benchmarking cases by 2d-DMM, 3d-DMM and
LS-DYNA
Uncertainties of estimating the spreading behaviour of the actual flows
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Thank you
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