耐震性評価のための地盤調査・土質試験の運用事例ワークショップ
土木学会，2021.11.16

降雨や地震による地盤災害と地盤調査

渦岡良介
京都大学防災研究所

6th International Conference on Engineering Geophysics
Al Ain, UAE, 25 – 28 October 2021

Role of geophysical survey
in geotechnical seismic analysis
地盤の動的解析における物理探査の役割
UZUOKA Ryosuke
Disaster Prevention Research InstituteKyoto University

Outline and Acknowledgements
 Slope behavior during rainfall and earthquake Matsumaru, T. and Uzuoka, R.: Three-Phase Seepage-Deformation Coupled Analysis about
Unsaturated Embankment Damaged by Earthquake, International Journal of Geomechanics, 16(5),2016. https://doi.org/10.1061/(ASCE)GM.1943-5622.0000699
 Xu, J., Ueda, K., & Uzuoka, R. (2021). Evaluation of failure of slopes with shaking-induced cracks inresponse to rainfall. Landslides 2021, 1–18. https://doi.org/10.1007/S10346-021-01734-1

 Recent geophysical survey

 Inazaki, T., Hayashi, K., Watanabe, F., Matsuo, K., Tokumaru, T., and Imamura, S., 2008. Groundtruth verification of an integrated geophysical investigation for the assessment of an earthen levee.
Proceedings of the 21th Annual Symposium on the Application of Geophysics to Engineering andEnvironmental Problems (SAGEEP2008).
 Takahashi, T., 2018. Soil permeability profiling using geophysical data. Annual Conference ofJapanese Society of Irrigation, Drainage and Rural Engineering, 2018. (in Japanese) Suzaki, A., Minato, S., Ghose, R., Konishi, C., & Sakai, N., 2017. Modelling time-lapse shear-wave
velocity changes in an unsaturated soil embankment due to water infiltration and drainage. First
Break, 35(8), 81-90.
 Thomas Planès, Justin B. Rittgers, Michael A. Mooney, Wim Kanning, Deyan Draganov, 2017.
Monitoring the tidal response of a sea levee with ambient seismic noise. Journal of AppliedGeophysics, 138, 255-263.

地盤の動的解析における物理探査（地盤調査）
 良質な不かく乱試料を用いた室内試験がない場合、原位置試験から力学的材料パラメータを経験的に推定する場合がある。物理探査で力学的材料パラメータを合理的に推定できると有用。
 地震前の斜面や盛土の初期条件（地下水位、飽和度分布）がその後の地震時挙動に影響するので正確に把握する必要がある。物理探査が時々刻々変化する初期条件をを推定できると有用。
 地震後の斜面や盛土の変状がその後の降雨浸透挙動に影響する。地震後の斜面や盛土内の状態を物理探査で知ることができると有用。

Overview of numerical method

Soil-water-air coupled analysis
 Porous media theory at finite strain (de Boer 2000, Schrefler 2002)
 Soil skeleton, pore water and pore air
 Static, quasi-static and dynamic problem

 Balance equations

 Mass and momentum balances of soil skeleton
 Mass and momentum balances of pore water
 Mass and momentum balances of pore air

 Constitutive models

 Bishop’s effective stress (skeleton stress)
 Darcy flow: interaction between soil skeleton and fluid Compressibility of pore water Compressibility of pore air
 Water retention curve (SWCC, WRC)
 Constitutive model for soil skeleton
 Cyclic elasto-plastic model, etc.

 Numerical method Mixed finite element method
 Newmark time integration

Numerical analysis flow
Soil conditions

Structure conditions

Model parameters

Finite element model
Boundary conditions
Initial conditions
Effective stress analysis

Earthquake motionModel parameters In-situ tests

 SPT (N-value, Soil profile, ground water) PS logging (S and P wave velocity)

 Laboratory tests with disturbed samples
 Particle size distribution test
 Permeability test

 Laboratory tests with undisturbed samples

 Density test Consolidation test (compression and swelling indexes) Shear test (friction and dilatancy angle)
 Undrained cyclic shear test (strain-dependent shear stiffness and damping, liquefaction
strength) When you do not have high quality undisturbed samples, Give up the analysis
 Use empirical relationship with in-situ test output

Simulation of laboratory tests
 Undrained/drained monotonic/cyclic shear tests
 Stress – strain relationship, stress path
 Strain-dependent stiffness/damping, liquefaction strength curve
15
Experiment
10
5
0
-5
-10
-15
-5
-2.5
0
2.5
Shear strain (%)

5

15
10
5
0
-5
-10
-15
0 10 20 30 40 50 60 70
Mean effective stress (kPa)

15
10
5
0
-5
-10
-15
0 10 20 30 40 50 60 70
5Mean effective stress (kPa)(a) Shear stress - shear strain relations(b) Effective stress paths
15
10 Simulation
5
0
-5
-10
-15
-5
-2.5
0
2.5
Shear strain (%)

0.6

Experiment (DA=10%)

0.5

Simulation (DA=10%)

0.4
0.3
0.2
0.1
0

1

10
Number of cycles

100Liquefaction resistance by in-situ sounding

Soil Behaviour in Earthquake Geotechnics (Ishihara, 1996)

Shear wave velocity by in-situ sounding

Soil Behaviour in Earthquake Geotechnics (Ishihara, 1996)

Soil dynamics

Shear wave velocity is not
a very sensitive measureof liquefaction resistance.

Soil Behaviour in Earthquake Geotechnics (Ishihara, 1996)

地盤の動的解析における物理探査（地盤調査）
 良質な不かく乱試料を用いた室内試験がない場合、原位置試験から力学的材料パラメータを経験的に推定する場合がある。物理探査で力学的材料パラメータを合理的に推定できると有用。
 地震前の斜面や盛土の初期条件（地下水位、飽和度分布）がその後の地震時挙動に影響するので正確に把握する必要がある。物理探査が時々刻々変化する初期条件をを推定できると有用。
 地震後の斜面や盛土の変状がその後の降雨浸透挙動に影響する。地震後の斜面や盛土内の状態を物理探査で知ることができると有用。

Matsumaru, T. and Uzuoka, R.: Three-Phase SeepageDeformation Coupled Analysis about Unsaturated
Embankment Damaged by Earthquake, International
Journal of Geomechanics, 16(5), 2016.
https://doi.org/10.1061/(ASCE)GM.1943-5622.0000699

BackgroundThe 2004 Niigata-ken Chuetsu earthquake (23rd Oct.)caused wide-spread area damages of embankments.

Niigata PrefectureTokyo
FukuokaPurpose
Heavy rain in
Hokuriku region
Rainfall intensity [mm/h]

50
40
30
20
10

0
7/1

Typhoon No.23
1200

Recorded at Ojiya city

1000
800

Accumulated Rainfall

600
400

Rainfall intensity
7/29

8/26

200
9/23

0
10/21

Time [day]Main reason of the damages?
However, there are a small number of researches
about seismic behavior considering rainfall.
Three-phase seepage-deformation coupled FE
analysis focused on this damage was performed.

Accumulated Rainfall [mm]• Nigata Prefecture
was affected by therainfall before thisearthquake.

Basic function
Overall density of mixtureρ = ρs + ρw + ρa

{

(

Soil

Air

Water

) }

= (1 − n )ρ sR + n s w ρ wR + 1 − s w ρ aR

Skeleton stress (e.g. Gallipol et al. 2003)
a
w
a
w
′
(
σ = σ − p I + s p − p )I
Gallipoli, D., Gens, A., Sharma, R. and Vaunat, J.: An elasto-plastic model for unsaturated soil incorporating theeffects of suction and degree of saturation on mechanical behavior, Geotechnique, Vol.53, No.1, pp.123-135, 2003.

Soil Water Characteristic Curve(Sugii et al. 2002)
w

(

w
s

w
r

)

w
e

s = s −s s +s

w
r

{

w
e

(

c

s = 1 + exp alg p + blg

)}

− clg

Sugii, T., Yamada, K. and Kondou, T. 2002. Rela-tionship between soil-water characteristic curve and void ratio,
Proceedings of ernational Conference, 1: 209-214.

Permeability coefficient of water and air

k

ws

=k

w
s

(s )

w ξk
e

k

as

a
s

(

= k 1− s

)

w ηk
e

Constitutive model for unsaturated soil (1)Yield function3f =η−α −k = 0
2Nonlinear evolution rule2 pp（Armstrong and Frederick, 1966） α = a be − αεd 3Armstrong. P. J. and Frederick. C.O.: A mathematical representation of the multiaxial Bauschinger effect, Technicalreport C.E.G.B.Report RD/B/N731, Berkeley Nuclear Laboratories, 1966.

In order to describe the large strain
a is reduced according to the value of the equivalent
plastic strain εdp(n)(a 0 − a1 )a = a0 −
1 + (a 0 − a1 ) exp(− C f ε dp ( n ) )Constitutive model for unsaturated soil (2)Non-associated flow rule Plastic potential function
∂g
∂g
 p 
3
p
p
εv = Dγe = γg=η − α + M m ln 2∂s∂p pa 
In order to describe cyclic loading of unsaturated soil
The volumetric strain εvp is changed depending on
the suction pc of unsaturated soil(c
D = D1 + (D0 − D1 ) exp − p c / pref

D0
D

D1

Deviatoricstress
Suction)Unsaturated soil
Saturatied soil
Mean skeleton
sterssGoverning equations (Uzuoka and Borja, 2012)
The momentum balance equation of the overall
three phase material
ρa s = div[σ′ − {s w p w + (1 − s w ) p a }I ] + ρb
The mass and momentum balance equations of thepore water and air
s w
s a ns w ρ wRwR  D p
wR D p
w wR
s


−
+
+
div
ρ
ρ
ρ
n
c
n
c
s
v
w
 Dt
K
Dt


 k ws+ div − gradp w + ρ wR b w − ρ wR a s  = 0
 g


(

(

)

)

s a
s w
 n 1− sw M a

D
p
D
p

− nρ aR c 
+ nρ aR c+ 1 − s w ρ aR divv s
ΘR
Dt

 Dt
 k asaaR aaR s 
+ div − gradp + ρ b − ρ a  = 0
 g


(

(

)

)

Uzuoka, R. and Borja, R.I.: Dynamics of unsaturated poro-elastic solids at finite strain, International Journal for
Numerical and Analytical Methods in Geomechanics, Vol.36, pp.1535-1573, 2012.

Outline of damaged embankment
Embankment in vicinity Joetsu Line 220k300m
Railway track
Collapsed soil
Beforecollapse

After collapse(Morishima et al. 2005)• Embankment was constructed in a valley of the Shinano River.
• The volume of collapsed soil was about 9,000 m3.
• The damaged area had a height of 7 m.
Embankment
material

Uc
Gs
D50
Fc
ρd
2.629 0.134mm 11.65 23.3% 1.29g/cm3

Cyclic triaxial test of embankment material
Embankment
material

Uc
Gs
D50
Fc
ρd
2.629 0.134mm 11.65 23.3% 1.29g/cm3

Procedure(1)Saturation (2)Drainua (3)Water absorption (4)Cyclic loading
pa

pa ua

Drained air and water condition

Case1： pc=14kPa
Case2： pc=4kPa
Case3： pc=0.3kPa

Input axial strain

Axial strain [%]Test cases

Undrained condition

3
2%
2
1.5%
1 0.1% 0.2% 0.5% 1%
0
-1
-2
-3
0
200
400
600
800 1000Time [min.]Cyclic triaxial test of embankment material
The parameters of embankment material were determinedfrom the simulations of cyclic triaxial test.
Experiment

20
00Pore water pressure [kPa]

100
80
60

200

400 600 800
Time [min.]20
400 600 800
Time [min.]

0
-100

400

Case1(pc=14kPa)
Case2(pc=4kPa)
Case3(pc=0.3kPa)

200

100

-200
0

1000

40

0
0

200

1000

300

50
100
150
200
Mean skeleton stress [kPa]

400

Stress difference [kPa]

40

300

Case1 (pc=14kPa)

100
0
-100
50
100
150
200
Mean skeleton stress [kPa]250

Case3 (pc=0.3kPa)

200
100
0
-100

400

Case1 (pc=14kPa)

200

-200
0

300

-200
0

250

Stress difference [kPa]

60

Stress difference [kPa]

80

400

Case1(pc=14kPa)
Case2(pc=4kPa)
Case3(pc=0.3kPa)

Stress difference [kPa]

Pore water pressure [kPa]

100

300

50
100
150
200
Mean skeleton stress [kPa]250

Case3 (pc=0.3kPa)

200
100
0
-100
-200
0

Simulation
50
100
150
200
Mean skeleton stress [kPa]The simulations could reproduce the experiments well.

250

Initial stress analysis
Seepage analysis (1)Seepageanalysis (2)19 mm/day

20
15
10
5
0
0

5

50

Observed rainfall
before earthquake

Dynamic response analysis

Estimate influence ofrainfall to seismic resistance

101085Time [day]

1090

1200

Recorded at Ojiya city

40

1095

1000
800

30

Accumulated Rainfall

20

600
400

Rainfall intensity

10
0
7/1

7/29

8/26
Time [day]

200
9/23

0
10/21

Accumulated Rainfall [mm]Annual rainfall

25

1000
Accel. [gal]Case 2 and 3

Rainfall intensity [mm/h]

Case 1

Rainfall intensity [mm/day]Steps of numerical simulations

500
0
-500
-1000
0

5

10

15
20
Time [sec.]

Max: 665gal
2530

Analytical conditions
Finite element model

30m

y
x

Embankment
Embankment

n485

5.5m

75m
39m

10m

n174

e79

Bedrock (medium grained sand Bedrockstone)
144m

In Case 3, rainfall poured on slope surface above
embankment seeped into embankment.

Degree of saturation before earthquake
Case1

Case2

Case3

Sr increased more largely at toe
in Case 2 and at top in Case 3.

Embankment

n174

Vertical disp. [m]n485

8
6 Observed
4 Settlement
2
0
-2
0
5
10

Vertical disp. [m]Time histories of vertical displacement

4
3
2
1
0
-1
0

Case3

15
20
Time [sec.]

Case2

Case2
Case1

25

30

Case3
Case1

5

10

15
20
Time [sec.]25

Larger displacement was obtained in Case 2 and 3.
Simulated disp. in Case 3 almost coincided with observed.

30

Conclusions
Three-phase seepage-deformation coupled analysis
focused on damage in the 2004 Niigata-ken
Chuetsu earthquake was performed.
By applying the rainfall before the earthquake,• Degree of saturation increased more widely.
• Dynamic response analysis showed larger
deformation and coincidence with measured.
• Liquefaction would occur in embankment andcause large strain.

地盤の動的解析における物理探査（地盤調査）
 良質な不かく乱試料を用いた室内試験がない場合、原位置試験から力学的材料パラメータを経験的に推定する場合がある。物理探査で力学的材料パラメータを合理的に推定できると有用。
 地震前の斜面や盛土の初期条件（地下水位、飽和度分布）がその後の地震時挙動に影響するので正確に把握する必要がある。物理探査が時々刻々変化する初期条件をを推定できると有用。
 地震後の斜面や盛土の変状がその後の降雨浸透挙動に影響する。地震後の斜面や盛土内の状態を物理探査で知ることができると有用。

Xu, J., Ueda, K., & Uzuoka, R. (2021). Evaluation of
failure of slopes with shaking-induced cracks in responseto rainfall. Landslides 2021, 1–18.
https://doi.org/10.1007/S10346-021-01734-1

1.3 Objectives and methods
The study of slope response to post-shaking rainfall is lacking but highly demanded.
Objectives
1. To examine slope’s performance under different external conditions(rainfall; shaking and rainfall);
2. To evaluate the effect of shaking-induced cracks on the seepage and deformation ofslope during the subsequent rainfall;
3. To evaluate the effect of shaking intensity and rainfall intensity on landslide kinematics;
4. To propose a method used for FEM modeling of slope response to post-shaking rainfall.
Methods
1. Centrifuge modeling
2. Numerical simulation

Today only centrifuge modelling is presented here.

2 Centrifuge model tests
ProgramCentrifuge model

50 g

Soil information

Test

Condition

Shaking
intensity

Rainfallintensity

A1

Only rainfallNone

30 mm/hA2

Shaking and rainfall

4.6 m/s2

30 mm/hA3

Repeatability of test A2

4.6 m/s2

30 mm/h

B1

Only rainfall

None

9 mm/hB2

Shaking and rainfall

4.6 m/s2

9 mm/hB3

Repeatability of test B2

4.6 m/s2

9 mm/hC1

Rainfall, shaking, and rainfall

4.6 m/s2

9 mm/hC2

Rainfall, shaking, and rainfall

3.0 m/s2

9 mm/hProperty

Value

PropertyValue

Dry density

1.50 g/cm3

Saturation

0.35

Relative density

85 %Void ratio

0.75

Permeability

4.4 mm/h(1.2E-6 m/s)

2 Centrifuge model tests
Rainfall simulator
Centrifugearm

Air pressure supply

Pressure control
Valve
Water tank
Water
Nozzles (water inlet)

Top view of container

Pressure control
Valve
Container
Air
Nozzles (air inlet)

Calibration was conducted to achieve
uniform rainfall

Slope model inside container

2.2 Response of slopes to shaking
Test

Shaking Rainfall
Condition
intensity intensity

A2

4.6 m/s2

30 mm/h Shaking and rainfall

B2

4.6 m/s2

9 mm/hShaking and rainfall Displacement vectors(b) Test B2(a) Test A2Sinusoidal input wave (1 Hz, 40 s)
6

1m

1m

 Top view of slope crest

Input motion

Acceleration (m/s

2

)

4

50 cm

(a) Plan view of slope in Test A2

2

Back wall

0-2

Front wall

50 cm(b) Plan view of slope in Test B2
Back wall

Crest

Crest

Downslope

Downslope

Front wall

-4
-6

0

5

10

15

20

25

30

35

40

Time (s) Displacement discontinuity caused cracks
near slope shoulder

2.3 Response of slopes to rainfallNone

30 mm/h Rainfall

A2

4.6 m/s2

30 mm/h Shaking and rainfall

B1

None

9 mm/hRainfallB2

4.6 m/s2

9 mm/hShaking and rainfall

 Soil displacement during rainfall
300

300
M3

Test A1

250

250

Test A2

200

Heavy
rain

150
100
50
0

0

10

20

30

40

300

50

200
150
100
50
0

0

10

200

Light
rain

150
100
50
0

0

10

20

30

Time (h)

150
100
50
0

0

10

40

50

30

40

50

150
100
50
0

10

20

30

Time (h)

40

50

M1

Test B1

250

Test B2

200

0

20

300
M2

Displacement (cm)

M1

50

200

Time (h)Test B1

250

Test B2

Displacement (cm)

M2

40

300
M3

Test B1

250

Displacement (cm)Marker30

Test A2Time (h)

300

M3

20

M1

Test A1

250

Test A2Time (h)Slope outline

M2

Test A1

Displacement (cm)A1

Displacement (cm)Shaking Rainfall
Condition
intensity intensity

Displacement (cm)Test

Test B2

200
150
100
50
0

0

10

20

30

Time (h) Heavy rainfall accelerated the failure ofslope with cracks

40

50

2.3 Response of slopes to rainfall Slope deformation

 Slope after failure(a) Test A1, heavy rain(c) Test A2, post-shaking heavy rain(b) Test B1, light rain(d) Test B2, post-shaking light rain(a) Test A1(c) Test A2(b) Test B1(d) Test B2

 Shaking-induced cracks changed landslide features during rainfall Rainfall intensity controlled landslide features of slopes with cracks

2.3 Response of slopes to rainfall
Test

Shaking Rainfall
Condition
intensity intensity

A1

None

 Effect of rainfall intensity on preferential flow
16

30 mm/h Rainfall

4.6 m/s2

30 mm/h Shaking and rainfall

B1

None

9 mm/hRainfallB2

4.6 m/s2

9 mm/hShaking and rainfall

Pore water pressure (kPa)A2

P2 in test A1

14

P2 in test A2

12

P3 in test A1

10

P3 in test A2

6
4
2
0

0

P3
P2

Pore water pressure (kPa)transducer

5
P2 in test B1

14

Pore water pressure

with heavy rainfall

8

16

Slope outline(a) Tests A1 and A2

P2 in test B2

12

P3 in test B1

10

10

15

20

25

20

25

Time (h)(b) Tests B1 and B2

with light rainfall

P3 in test B2

8
6
4
2
0

0

5

10

15
Time (h) Preferential flow due to cracks was evident during heavy rainfall

4 Conclusions
Experiments
1. Once shaking caused cracks on the slope surface, the pattern and severity of the slope
failure caused by the following rainfall became different, compared with the slope
subject to only rainfall.
2. Shaking-induced cracks changed landslide features during rainfall and heavy rainfall
accelerated the failure of slope with cracks.
3. The effect of cracks on preferential flow depended on the rainfall intensity.

地盤の動的解析における物理探査（地盤調査）
 良質な不かく乱試料を用いた室内試験がない場合、原位置試験から力学的材料パラメータを経験的に推定する場合がある。物理探査で力学的材料パラメータを合理的に推定できると有用。
 地震前の斜面や盛土の初期条件（地下水位、飽和度分布）がその後の地震時挙動に影響するので正確に把握する必要がある。物理探査が時々刻々変化する初期条件をを推定できると有用。
 地震後の斜面や盛土の変状がその後の降雨浸透挙動に影響する。地震後の斜面や盛土内の状態を物理探査で知ることができると有用。

Recent geophysical survey

Integrated geophysical investigation of river levee(Inazaki et al. 2008)

Integrated geophysical investigation of river levee(Inazaki et al. 2008)

Soil permeability profiling using geophysical data

(Takahashi et al. 2018)

Modelling time-lapse shear-wave velocity changes(Suzaki et al. 2017)

地盤の動的解析における物理探査（地盤調査）
 良質な不かく乱試料を用いた室内試験がない場合、原位置試験から力学的材料パラメータを経験的に推定する場合がある。物理探査で力学的材料パラメータを合理的に推定できると有用。
 地震前の斜面や盛土の初期条件（地下水位、飽和度分布）がその後の地震時挙動に影響するので正確に把握する必要がある。物理探査が時々刻々変化する初期条件をを推定できると有用。
 地震後の斜面や盛土の変状がその後の降雨浸透挙動に影響する。地震後の斜面や盛土内の状態を物理探査で知ることができると有用。