Development of a Near Real-Time Early Warning System on Landslides
Triggered by Heavy Rainfall along the Mekong River, Cambodia
By: DOK Atitkagna, Doctoral Student, Research Center on Landslides, Disaster Prevention
Institute, Kyoto University
Abstract
Situated in the southwestern part of the Indochina peninsula and roughly square in shape,
Cambodia is covered by wet humid climate, and dominant features: Tonle Sap and the Mekong River
which traverses the country from north to south. The whole country is wet, the soil is fertile, and therain forest is thickly green. Simultaneously, this homeland is very susceptible to natural disasters,
especially landsliding. After a continuously heavy rain over night, downstream areas were flooded,inducing various types of mass movement in the upslope areas. The Mekong lowland, in particular thearea along the Mekong River bank holds the highest population, economically sounds and has
remarkable development progress. Catastrophic landslides have frequently occurred and attacked thedown-slope area under heavy rainstorm condition. Every time, roads have been cut, houses weredamaged, and claimed lives of dozens of people.
Obviously, landslides triggered by heavy rainfall along the Mekong River are now major andcomplex issue that significantly interrupts the development of Cambodia. It is well and widely
recognized throughout the nation, but mechanism, prediction and assessment of those phenomena in
Cambodia are poorly understood, particularly, (1) shallow landslide triggering mechanism in thetropical soils is not yet uncovered; (2) mechanism of precursor signs of landslides, i.e., accelerating
displacement is not yet solved; (3) even though a certain number of networked rain gauges get
operational near real-time, optimization of water penetration coefficients in each district should be
combined with various factors. Therefore, this study aims at studying mechanism of landslides in thetropical soils by using ring shear apparatus invented by DPRI, and the Tertiary Creep mechanism inhelp to the early warning on rainfall–induced landslides and apply Japanese Soil-Water Index to southeastern Asia countries for landslide early warning.
The expected outcomes of this study are (1) to formulate the empirical equation of tropicalsoil characteristics applied in the south-east Asia countries, (2) to understand the failure mechanism of
the tropical soils, which significantly influences the formula variables, (4) to propose a numericalmodel using DEM (Discrete Element Method) or FEM (Finite Element Method) validated in ASEAN
regions if possible and (4) to predict and/or warn the rain-induced landslides through the application of
TRMM and Tank Model.
Keywords: ring shear apparatus, soil-water index, Tertiary creep, tank model, TRMM.

6/26/2010

Doctoral research plan
“Development of a near real-time
early warning system on landslides
triggered by heavy rainfall along theMekong river, Cambodia”

Contents
1. Introduction
2. Problem setting
3. Objectives of research
4. Research methodology
5. Expected outcomes

By: DOK Atitkagna

Introduction
Location: Southwestern partof the Indochina peninsula.
Boundary: Thailand & Laoson the North, Vietnam on
the East & Southeast, andGulf of Thailand &Thailand on the West &Southwest.
Dominant features: Tonlé Sap
and the Mekong River
traversing from North toSouth.

Problem setting
1) Shallow landslide triggering mechanism inthe tropical soils is not yet uncovered.
2) Mechanism of precursor signs of landslides,
i.e., accelerating displacement is not yetsolved.
3) Even though a certain number of networked
rain gauges get operational near real-time,
optimization of water penetration coefficientsin each district should be combined withvarious factors.

Objectives

Methodology

1. To study mechanism of landslides in thetropical soils using ring shear apparatus
invented by DPRI.
2. To study the Tertiary Creep mechanism
in help to the early warning on rainfallinduced landslides.
3. To apply Japanese Soil-Water Index tosouth-eastern Asia countries forlandslide early warning.

The study mechanism oflandslides in the tropical soils
by ring shear apparatus inDPRI, Kyoto University1

6/26/2010

Examples of landslides in Indonesia

Nov. 2008 Campaka landslide, Indonesia
Sourcearea

Houses destroyed
18 residents killed

Head scarp

Source area

Ring-shear tests for reproduction of landslide movement

Results of tests to simulate theinitiation of the Minamata
landslide (BD = 0.86) (afterSassa et al. 2004a).

Simulating
the sliding
surface
NormalstressSlidingsurfaceaxis

Normalstress

r st
Shea
Sampleress

undrained shear box

Methodology
The study the Tertiary Creepmechanism in help to theearly warning on rainfallinduced landslides

The concept of creep in soils
In many landslides, the failures are preceded by accelerated trend ofdisplacement. It is associated with crack growth, soil particles
rearrangement and shear surface evolution.
A slope failure seldom
occurs without any creep
deformation and fissures.
Creep deformation isexpressed as a timedependent deformation,
or deformation underconstant stress andtemperature.

2

6/26/2010

Literature reviews

Time prediction of landslides

In landslide filed, failure-time prediction method oflandslide have been widely developed by many
researchers: Saito and Uezawa (1960, 1966) as a start,Saito (1968), Kawamura (1984), Fukuzono (1978, 1982,1985), Voight (1988, 1989), Azimi (1988), Hayashi et al.
(1988), etc.
As mentioned above, only the two methods establishedby Saito and Uezawa (1960, 1966), and Fukozono (1985)
based on the creep rupture theory are more precise inestimating appropriate failure time of a slope being
previously monitored by creep deformation.

• 1965 – Saito (on Secondary and Tertiary creep) : proposed aLiterature reviews (cont.)

Experiment plan

Recently, Minamitani (2007), Ekaterina, and Chiyonobu
conducted research on the Tertiary Creep Mechanism byincreasing constant pore-water pressure and shear-stressdevelopment to understand the story behind the empirical
relationship found by senior researcher Fukozono.
The most recent research by Taichi(2007) on mechanismof Tertiary Creep deformation for landslide failure time
prediction. The study focused on Tropical soil characteristics
in South-east Asia countries on Tertiary Creep mechanism inparticular to displacement and time variation with constantσ,τ and u. However, the number of data are not enough forappropriate failure time prediction of landslide.

To study mechanism of landslides in tropical soils by ringshear apparatus (invented by DPRI) based on Tertiary
Creep deformation theory in help to the early warning on
rainfall–induced landslides, pore-water pressure control
tests are to be undergone under combined conditions ofparticular normal stress and shear stress with pore-waterpressure change to simulate the potential sliding surface
condition in the heavy rainfall.
Thus, the originality is the first pore water pressure control test
by ring shear apparatus to simulate heavy rainfall induced
landslides. Especially, nobody did those tests by applying
cyclic or actual groundwater change pattern to thesoils/sands.

Ring shear apparatus DPRI-Ver. 7(Undrained testing and pore pressure monitoring)

Ring shear tests withsilica sands #8 & masa
sands and actual
landslide’ sliding surface
soils (brought fromIndonesia, Cambodiaand Japan) on Tertiary
creep by applying actual
ground water pressure
pattern.

Numerical simulation ofcreeping to develop mostappropriate method forlandslide early warning.

Shear boxØinner: 27cm
Øouter: 35cm

method for predicting the time of failure of a slope based ongraphical analysis of extensometer monitoring data.
• 1985 – Fukuzono (on Tertiary creep):found log of acceleration is proportional to the log ofvelocity of surface displacement.
d2x/dt2=A(dx/dt)αwhere x is surface displacement, t is time, and A and α areconstants.
• Yet, higher accuracy needs to be improved. And, the mechanismof creep deformation is still not yet well-understood at the present.

System for back-pressure control- Technicalparameters ofDPRI-7:- Ratio of max.
height/width: 2.88
- Max. normal
stress: 500kPa- Max. shear speed:
300cm/s (adapted toshallow landslides)

Increase thepore waterpressure
ControlPC

Max possible heightof sample 115cm

Shearing direction

Shear area 386.56cm2Airtank

Water tank

Sample boxof the ringshear
apparatus3

6/26/2010

Planned experimental conditionsPlanned experimental conditions (cont.)D) σ (normal stress)= (1)100kPa(2) 50kPa for additional testA) Testing materials:(1) mixture of silica sands #8 (meangrain size of SS8 0.06mm) withbentonite clay(2) masa sands (weathered granite sands)(3) tropical soils from landslide sites

E) du/dt=B) Slope inclination ( ):(1) 30° (2) 25°(3) 20°(4) 15°(1) constant(2) simulating to real
groundwater record(3) cyclicF) Initial BD=Δu/Δσ (saturation degree by Sassa,1988):(1) BD >0.95(2) BD <0.95C) Over consolidation ratio OCR:
(1) 1.0 (2) 4.0 (3) 2.0

Test conditions

Test results, du/dt=1kPa/s• OCR = 1.0 (normally consolidated)• CO2 circulation: 30 minutes• Pore water: tap water (not de‐aired water),
circulation for 1 overnight• BD = 0.66 (normal stress = 50 100 kPa)
• Normal stress ( ) = 100 kPa• Shear stress (τ) = 54 kPa• Slope inclination ( )= (tan ‐1 (τ/σ)) = 30°• u0 = 15 kPa• du/dt = 1 kPa/s.

600

Shear displacement (cm)500
400
30020010000-10050100150200250300

Tme (s)Expected Outcome

Test results, du/dt=1kPa/s
10000

100100.10.0001

100.150100150Time (s)2002500.001

0.01

0.1

1300
Acceleration (cm/s2)

1/v (s/cm)

1000

0.01= 1.1

Velocity (cm/s)

0.001

Formulate the empirical equation of tropical soil
characteristics applied in the south-east Asia
countries.
Understand the failure mechanism of the tropicalsoils, which significantly influences the formulavariables.
If possible, propose a numerical model using DEM(Discrete Element Method) or FEM (Finite ElementMethod) validated in ASEAN regions.
Predict and/or warn the rain-induced landslides
through the application of TRMM and Tank Model.

0.00014

6/26/2010

Thank you for your attention!!!

5