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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