rockfall in northern taiwan: mechanism, numerical...

The case study of Badouzihrockfall in northern Taiwan: mechanism, numerical simulation and hazard assessment

Ching-Fang Lee, Ting-Chi Tsao, Lun-Wei Wei, Wei-Kai Huang

Disaster Prevention Technology Research Center, Sinotech Engineering Consultants, INC., Taipei, Taiwan

June 2, 2016

13th CongressINTERPRAEVENT 2016KKL Lucerne, Switzerland

Outline

01

Introduction

02

Study area and

methodology

03

Investigation

and simulation

04

Conclusions

Introduction

01

Introduction01

Taiwan Swiss

Population 23 million 8 million

Highest Mt. 3,952 m 4,634 m

Annual Prec. 2,502 mm 1,537 mm

Introduction01

(source: NASA)

Introduction01 Rock fall

Debris flow

Landslide

Landslide

Introduction01

Rockfall events Alone Highway No.2

(1994~1996；2004~2013)

This event

(Event data from MOTC, Taiwan)

# of events

Highway No.2

Yi-Lan

New Taipei

Taipei City

Keelung

LEGEND

Introduction

About the rockfall disaster

The Badouzih rockfall was triggered by rainfall on August31st, 2013 in Keelung City in northern Taiwan.

The highest intensity rainfall of 94.5mm/h occurred, leadingto a rockfall disaster at 16:19 in which a passing car wasstuck on Provincial Highway No. 2

More in Wei et al. (2014), Engineering Geology, 183: 116-126.

The boulder had a weight of roughly 115 ton and dimensionsof 4.5 m × 4 m × 3.8 m; another roughly 235 ton boulderremains perched on the ridge.

01

GIS center, FCU

2013/08/31-9/1 - Keelung station

Time [hr]

10 12 14 16 18 20 22 24 2 4 6 8 10 12 14 16

pre

cip

ita

tio

n [

mm

]

0

20

40

60

80

100

120

effe

ctiv

e c

um

ula

tive

pre

cip

itatio

n [m

m]0

100

200

300

400

500

precipitation

effective cumulative precipitation

2013/09/01

occurrence of rockfall

(source: https://www.youtube.com/watch?v=8wWuH7MIeCA)

Introduction01

Badouzih rockfall

intensity 10yr 25yr 50yr 100yr 200yr

60 min 77.1 88.4 96.1 103.2 110.1

Imax=94.5mm/hr 50 yr rainfall intensity (96.1mm/hr)

duaration [min]

0 500 1000 1500 2000 2500

rain

fall

inte

nsity [

mm

/hr]

0

50

100

150

20010 yr

25 yr

50 yr

100 yr

200 yr

08/31 Rainfall

intensity-duration-frequency curve (IDF)

Introduction01

(source: United Daily News, Sep.3, 2013)

Study area and

methodology

02

Study area and methodology02

terrain production

unmanned aerial vehicle (UAV)

airborne and terrestrial LiDAR

DTM

field survey

geological drilling and material test

field investigation numerical simulation

RAMMS::ROCKFALL

failure mechanism hazard map

1 2 3

geological setting

02 Study area and methodology

Schmidt hammer test: rock strength=250~290kg/cm2

The study area consists mainly of calcareous massivesandstone belonging to the Taliao Formation (Tl) whichfeatures ridges and promontories along the northerncoast.

The attitude of the bedding plane is approximatelyN81°E/8°S and the attitude of slope surface at the sourcearea is about N70°W/35°N, forming an anaclinal slope.

Two interlocking joint sets: N 72°W/88°N (J1), N16°E/88°N (J2)

J2

J1

68K

8

8888

Investigation and

simulation

03

Investigation and simulation03

Boulder #2 remained on the hilltop (Sep., 2013)


rockfall trajectory on the cross-sectional profile.

123

3 1

J1

J2

Geological investigation

Investigation and simulation

Rockfall trajectory (Boulder #1)

03

12

main path : 1

path : N10o/E 2

toward north direction

1

2

UAV photo provided by GIS.FCU



toppling

sliding

rolling

falling

bouncing

1

2

3

4

5

1 2 3

4 5


Investigation and simulation

rockfall mechanism (Boulder #1) on the longitudinal profile.

03



Scenario 1 : Boulder 1 Scenario 2 : Boulder 2

parameter validation hazard map production

single rock multi-rocks

Parameter value sourceboulder size[m] 4.54 * 4.09 * 3.84 m in-situ measuring

elevation of source area [m] 119 in-situ measuringdensity [kg/m3] 2,650 experimental result

release point (x, y) (329028, 2781980) aerial image(TWD97)

initial rotational velocity (X, Y, Z) (rad/s) (0.3, 0.5, 0) video record

rock type Equant_1.3calculated by RAMMSrock mass [ton] 115.44

rock volume [m3] 42.75

Parameter of the boulder

Geologic parameters used in the RAMMS simulation (resolution of DEM: 5m)

No. terrain material friction reference

1 TI (S.S) colluvium 0.25 (soft) in-situ measuring

2 TI(S.S and Sh. interbedded) colluvium 0.25 (soft) in-situ measuring

3 Road and Fishery Harbor concrete 0.40 in-situ measuring

4Forest type Height [m] Drug [kg/s]

medium 1.5-3.0 1500 in-situ measuring

A

B

GIS center, FCU

Boulder #1- validation (the event in the study)

Boulder #2- prediction(remains on thehilltop)


03 Investigation and simulation

Scenario 1 : Boulder 1

(a) 3D rockfall trajectory

(b)the real rockfall trajectory on the aerial image

(c) Simulation trajectory in RAMMS

The result of numerical simulation RAMMS::ROCKFALL



Horizontal distance (m)

0 20 40 60 80 100 120 140 160

Kin

etic

ene

rgy (K

J)

0

10x103

20x103

30x103

40x103

50x103

60x103

70x103

80x103

90x103

100x103

Ve

locity (

m/s

)0

10

20

30

40

Kinetic energy (Rocfall-Wei(2014))

Kinetic energy (RAMMS)

Velocity (Rocfall-Wei(2014))

Velocity (RAMMS)

Scenario 1 : Boulder 1 The comparison of Rocfall 2D and RAMMS:: Rockfall 3D

Velocity and kinetic energy:3D model are less than 2D model.

Difference in model: rock shape topographic model accuracy Forest drag



Parameter valueboulder size[m] 5.3 * 5.8 * 4.9 m

elevation of source area [m] 122density [kg/m3] 2,650

release point (x, y) (329028, 2781980)

initial rotational velocity (X, Y, Z) (rad/s) (0.3, 0.3, 0)

rock type Equant_1.2rock mass [ton] 234.44

rock volume [m3] 88.60Number of rocks 100

Parameter used for multi-boulder simulation



kinetic energy (KJ) – Q95% Boulder velocity (m/s) – Q95% jump height (m) – Q95%

02 Study area and methodology

Diagram of hazard levels as a function of probability and intensity (BUWAL, 1999)

2D Rockfall hazard map

O. Lateltin et al., Landslide risk management in Switzerland. Landslides (2005) 2: 313–320.

1-30 yr30-100 yr100-300 yr

G. B. Crosta, F. Agliardi. A methodology for physically based rockfall hazard assessment. Natural Hazards and Earth System Science, 2003, 3 (5), pp.407-422.

Crosta and Agliardi (2003)

Lateltin et al. (2005)

03 Investigation and simulation Scenario 2 : rockfall hazard map

Intensity criteria form Crosta and Agliardi 2003)Intensity criteria form Lateltin et al.(2005)

Conclusions

04

A good event documentation is vital to rockfall modelingcalibration, this case study shows how a well documented rockfallevent could contribute to numerical simulation.

RAMMS::ROCKFALL is able to integrate the detailed block shape,terrain material, and initial condition for modeling three-dimensional rockfall event. And the simulation shows good result.

For hazard mitigation, the hazard map which associated with rockmass strength assessment (frequency) and numerical simulation(intensity) around alpine region can help predicting future rockfalloccurrence.

Conclusions04

Conclusions04

Photo: Keelung City Government

What happened to Boulder #2 ??

Conclusions – UAV application 04

DJI-P3P

30 March, 2016 (resolution: 5cm)Badouzih harbor

UAV photo provided by Sinotech

[email protected]://dptrc.sinotech.org.tw

13th CongressINTERPRAEVENT 2016KKL Lucerne, Switzerland

Ting-Chi TSAODisaster Prevention Technology Research Center, Sinotech Engineering Consultants, INC.

Special thanks to RAMMS

team of WSL, for providing

the ROCKFALL model in the earlier stage of this study

rockfall in northern taiwan: mechanism, numerical...

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