MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Destabilization of a caisson-type breakwater
by scouring and seepage failure of the seabed
due to a tsunami
T. IMASE (Nagoya Institute of Technology, Nagoya, Japan )
K. MAEDA (Nagoya Institute of Technology, Professor, Nagoya, Japan )
M. MIYAKE (Toyo construction Co., Ltd., Doctor, Hyogo, Japan)
Y. SAWADA (Toyo construction Co., Ltd., Doctor, Hyogo, Japan)
H. SUMIDA (Toyo construction Co., Ltd., Hyogo, Japan)
K. TSURUGASAKI (Toyo construction Co., Ltd., Doctor, Hyogo, Japan)
ICSE2012 20120829(Wed)-31(Fri)
Topics
Destabilization of a caisson-type breakwater
by scouring and seepage failure of the seabed due to
a tsunami
[Part.1] Introduction
[Part.2] Tsunami experiment
using
centrifuge model test
[Part.3] Numerical simulation
using
SPH method
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Introduction
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
In 46 minutes after earthquake In 31 minutes after earthquake In 26 minutes after earthquake
Introduction(The Great East Japan Earthquake)
Kamaishi port
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri)
Marine
Hazard
Ocean
wave
Wave
Hazard
Ground
Hazard
Tsunami
Wave
Hazard
Ground
Hazard
Experimental methodology using centrifugal device
Periodic waves (Ocean wave)
Mass movement (Tsunami)
Introduction
Development of
Numerical analysis using SPH method
cyclic loading Seepage Wave force
cyclic loading
The ground hazard mechanism by the tsunami is not understood.
Clarification of damage mechanism
with interaction of the tsunami, seabed soil and structure
A past tsunami research has been discussing damage of marine structure with the interaction of the tsunami and the structure.
i
S
g
a
P
2
.
2
Tanimoto (1994) et al. eq. :
ICSE2012 20120829(Wed)-31(Fri)
Introduction - Estimation of damage -
Sliding・Falling crosscurrent and Scouring with
vortex Bearing capacity failure Liquefaction Sliding・Falling Liquefaction Tractive force Bearing capacity failure Seepage Liquefaction Tractive force Seepage cyclic loading Tsunami Anaseism Wave Tsunami force Overflow Seabed soil Liquefaction Bearing capacity Seepage Bachrush Wave Tsunami force Seabed soil Cyclic loading
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Tsunami experiment with
drum-type centrifuge device
ICSE2012 20120829(Wed)-31(Fri)
Maximum acc. 440G （600rpm）
Dimensions Model Proto type
（Maximum acc.）
Diameter 2.2 m 3041 m Width 0.3 m 132 m
Depth 0.3 m 132 m （Ground 32 m) Maximum force 3.7 ton 1628g-ton
26 10 10 護岸 ゲート 50 239 338 波高計3 波高計1 波高計2 単位 (cm) 1：3 Model area：about 3.4 m
Toyo construction Co., Ltd.
Seabed soil (Toyoura-sand: Dr=40%) Rubble mound (Gravel: 2.9mm) Reservoir area： About 3.5 m 300rpm Caisson-type breakwater
Tsunami experiment with drum-type centrifuge device
Model test device
The experiment study used a 2.2 m diameter
drum-type centrifuge device. The tsunami was
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Gage points Maximum incident wave Maximum overlapping wave
CH 1 near the gate 0.69 m 2.58 m CH 2 near the breakwater 0.77 m 2.39 m
Tsunami experiment with drum-type centrifuge device
Tsunami experiment in a 32 g field
0 10 20 30 40 50 60 0 1 2 3 Duration time, t (s) W ave h ei gh t, η (m
) CH1 Centrifuge model test CADMAS-SURF
Maximum overlapping wave: 2.58m
Maximum incident wave: 0.69m
The experimental wave pressure were as large as than the results obtained using Tanimoto’s equation or Goda equation.
Tsunami force
0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m 2 ) H ei ght , z (m ) 遠心模型実験による最大波圧 遠心模型実験による段波圧 谷本らの式（最大波圧） 谷本らの式（段波圧） 池野ら 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m 2 ) H ei ght , z (m ) 遠心模型実験による最大波圧 遠心模型実験による段波圧 谷本らの式（最大波圧） 谷本らの式（段波圧） 池野ら 0 1 2 3 4 0 10 20 30 Length, L (m) L if t pr es sur e, Pd ( kN /m 2 ) 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m2) He igh t, z ( m )Centrifuge model test Tanimoto et al. Goda eq. 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m2) He igh t, z ( m )
Centrifuge model test Tanimoto et al. Goda eq. 0 1 2 3 4 0 10 20 30 Length, L (m) L if t pr e ss ur e , Pd ( kN /m 2 )
ICSE2012 20120829(Wed)-31(Fri)
Direction of the tsunami
Offing Shore
Movie （Click fig.)
Tsunami experiment with drum-type centrifuge device
Deformation of breakwater, rubble mound and
seabed soil
The breakwater was slided
Shear deformation occurred
Rubble mound and seabed soil
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Tsunami experiment with drum-type centrifuge device
Slide of the breakwater
Shear deformation Blowout of stone and sand from
the mound and the ground
Shore Offing (a) A B C D E 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0 100 200 300 Duration time, t (s) M om ent t ha t a ct s on br ea kw at er , M ( kN ) Maximum bore pressure Maximum overlapping wave pressure
The breakwater was slided (points A and B) when the maximum bore
pressure acted.
Rubble mound and seabed soil was scoured while continuous wave
pressures were acting (points B-E).
Shear deformation occurred in the rubble mound and the seabed soil, and
decreased the bearing capacity.
Deformation of breakwater, rubble mound and
seabed soil
ICSE2012 20120829(Wed)-31(Fri)
R P a q w q w s c F h s ' sin ' ' tan tan 1 sec ' tan ' ' Deformation velocity by PIV analysis
Bishop method 1.0 0.0 0.5 [m/s]
0
.
1
91
.
0
sF
Safety rate of circular slide
Shrear strain
Deformation of rubble mound and seabed
soil due to tsunami
Discussion of bearing
capacity destruction
Tsunami experiment with drum-type centrifuge device
Breakwater Rubble mound Seabed ground Direction of the tsunami Circular slip surface analysis 0 50 100 [%]
Shear deformation occurred in the rubble mound and the seabed ground with move of the breakwater.
And, the safety rate of circular slide was smaller than 1.0.
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
PWP４~PWP５ (near the ground surface)：
imax≒0.65 893 . 0 8538 . 0 1 1 656 . 2 1 1 e G icr s PWP4 PWP3 PWP5 PWP6 PWP2 PWP1
PWP2~PWP4 (into mound)：imax≒0.8 PWP2~PWP5 (into mound) ：imax≒0.5
10 20 30 40 50 0 0.5 1 H ydr aul ic gr adi ent in R ubbl e m ound , i R ubbl e m ound Duration time, t (s) PWP3-PWP1 PWP1-PWP4 PWP4-PWP2 PWP2-PWP5 PWP2-PWP6 Rubble mound 10 20 30 40 50 0 100 200 300 Duration time, t (s) M om ent t ha t a ct s on br ea kw at er , M ( kN ) A B C D E Ground surface 10 20 30 40 50 0 0.5 1 H ydr aul ic gr adi ent in t he gr ou nd, i gr oun d Duration time, t (s) PWP3-PWP4 PWP4-PWP5 PWP5-PWP6
Tsunami experiment with drum-type centrifuge device
Scouring and blowout with seepage flow
We calculated the hydraulic gradient
using the measured pore water pressure.
The results, the hydraulic gradient increased from the center of the
breakwater bottom toward the shore while the continuous wave pressure was acting.
ICSE2012 20120829(Wed)-31(Fri)
Numerical simulation
using SPH method
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Numerical simulation using SPH
Layer of Solid Air Water Porous material, soil sf f fs f Layer of Fluid
Total volume fraction: 1 = (Volume fraction: n) + (Volume fraction: 1-n) Superposition
of fluid-solid layers
Interaction body force
Soil-fluid coupling in the SPH method calculate fluid phase and solid phase, and the obtained results are overlapping by Darcy's low.
) ( 2 f s f s f k g n v v f n：Porosity g：Acceleration of gracity ρf：Density of fluid k：Permeability vs：Velocity of solid vf：Velocity of fluid
Soil-fluid coupling
Seepage around sheet pile (K. Maeda, M. Sakai (2004))
Superposition of smoothed physical values
Smoothed physical values by using smoothed function for each particle
x
Limited zone of influence
x1 x2 o Particle : i Particle : j rij xi xj κhi hi
Smoothed Particle Hydrodynamics
f
(
x
)
W
(
x
x'
,
h
)
f
(
x'
)
d
x'
The feature of the SPH method is as follows;
Mesh free
Lagrangian method
Initial modeling is easy.
ICSE2012 20120829(Wed)-31(Fri)
Numerical simulation using SPH
Comparison between experimental
result and numerical analysis result
Tsunami experiment
using centrifuge device
Numerical Analysis using SPH method i h 粒子（質点） 影響半径 ゲート 300rpm 海底地盤 ケーソン式 防波堤 捨石 マウンド NG Superposition of smoothed physical values
Smoothed physical values by using smoothed function for each particle
x
Limited zone of influence x1
x2 o Particle : i Particle : j rij xi xj κhi hi 防波堤の滑動 マウンド・地盤のせん断変形 捨石・地盤の噴出 防波堤 捨石マウンド 海底地盤 円弧 すべり解析 0 50 100 [%]
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) Tsunami 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m2) H e ight , z (m ) 遠心模型実験による最大波圧 遠心模型実験による段波圧 谷本らの式（最大波圧） 谷本らの式（段波圧） 池野ら 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m 2 ) H e ight , z (m ) 遠心模型実験による最大波圧 遠心模型実験による段波圧 谷本らの式（最大波圧） 谷本らの式（段波圧） 池野ら 0 1 2 3 4 0 10 20 30 Length, L (m) L if t pr e ss ur e , Pd ( kN /m 2 ) 0 1 2 3 4 0 10 20 30 Length, L (m) L if t pr e ss ur e , Pd ( kN /m 2 ) 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m 2 ) He igh t, z ( m ) Exp. Numerical analysis Tanimoto et al. 0 10 20 30 -2 -1 0 1 2 Wave Pressure, Pd (kN/m2) He igh t, z ( m ) Exp. Numerical analysis Tanimoto et al. i S
g
a
P
2
.
2
Tanimoto(1994) et al. eq.
Standard in technology of facilities in harbors
P
s第1波襲来時
Wave pressure that acts on breakwater
Comparison between experimental result and numerical analysis result
ICSE2012 20120829(Wed)-31(Fri) 0 10 20 30 40 50 60 70 80 90 100 -80.0 -60.0 -40.0 -20.0 0 20.0 40.0 60.0 80.0 M a rgi n of be a ri ng c a pa c it y, (kN /m ) Duration time, t (s) Exp. Numerical analysis Numerical analysis(EPWP)
Margin of bearing capacity
Margin of bearing capacity＝
Bearing capacity strength
－
Tsunami force
－
Bearing capacity decrease in breakwater due to
increase of excess pore water pressure
in the ground
Margin of bearing capacity
Initial decrease is the same.
The decrease in the safety factor of the breakwater was larger when the excess pore water pressure in the ground was taken into consideration
Comparison between experimental result and numerical analysis result
R P a q w q w s c F h s ' sin ' ' tan tan 1 sec ' tan ' ' MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
t = 3.30 s
result of SPH analysis（flow velocity vector）
[m/s] t = 2.70 s t = 5.00 s t = 6.00 s ① ② ③ ④ 0.0 0.3 0.6 0.9 1.2 t=15s t=30s Δη=50mm Δη=80mm
Centrifuge model test
Slide of the breakwater
Shear deformation Blowout of stone and sand from
the mound and the ground
Shore Offing
(a) 1g channel test
Comparison between experimental result and numerical analysis result
Seepage flow into rubble mound and seabed soil
Weight：W Lift force：LF Tractive force ：τ Soil particle friction：Fr Close up Weight：W Lift force：LF Tractive force ：τ friction：Fr Close up Excess pore water pressure：ue High-speed flow is caused in the rubble mound. As a result,
seepage flow was generated on the seabed soil surface.
ICSE2012 20120829(Wed)-31(Fri) 10 20 30 40 50 0 0.5 1 H ydra ul ic gra di e nt in t he ground, i g ro u n d Duration time, t (s) Exp.(PWP3-PWP4) Exp.(PWP4-PWP5) Exp.(PWP5-PWP6) Numerical analysis(PWP3-PWP4) Numerical analysis(PWP4-PWP5) Numerical analysis(PWP5-PWP6)
ij ej ei f j i ij H H g P P i f i P ei H ij g ：Density of fluid ：Acceleration of gravity：Total head of measurement point i ：Elevation head of measurement point i ：Distance of measurement point i and j
Hydraulic gradient into seabed soil
20 30 40 CL Unit : mm PWP8 PWP9 PWP7 PWP3 PWP4 PWP5 PWP6 PWP2 PWP1 35 4@ 25 P1 P2 P3 P4 P5 150 43.5 Tsunami
: Pore water pressure meter : Wave pressure meter
Numerical simulation using SPH
In the outcome of an experiment and the analytical result, the value is
different. Behavior looks like.
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Numerical simulation using SPH
Tsunami simulation
in virtual coastal area
ICSE2012 20120829(Wed)-31(Fri) 1,000 350 30 210 50 50 10 1 15 1:3 I.W.L +35.0 I.W.L +20.0 Unit : m shore offing
WL1 WL2 WL3 Measurement of wave level
1：2 I.W.L +20.0 8.8 15 2 10 Caisson-type Breakwater Rubble mound Seabed Impermeability layer Impermeability layer offing shore Measurement of wave pressure Unit : m PWP1 PWP2 PWP3 PWP4 PWP5 PWP6 PWP7 PWP8 PWP9 PWP10 PWP11 PWP12 PWP13 PWP14 PWP15 PWP16 PWP17 PWP18 PWP19 PWP20 PWP21 PWP22 PWP23 PWP24 PWP25 PWP26 PWP27 Marine model
Caisson-type breakwater model
Tsunami simulation in virtual coastal area
Numerical simulation using SPH
Stability of breakwater due to tsunami was investigated using a standard model of coastal area. A tsunami was generated by dam break. The permeability coefficients of the rubble mound and the seabed soil were set as 1×10-2 m/s and 2×10-5 m/s.
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) 0 100 200 0 10 20 Duration time, t (s) W a ve l e ve l, η (m ) WL1 WL2 WL3 0 20 40 60 80 100 0 10 20 Duration time, t (s) W a ve l e ve l, η (m ) WL1 WL2 WL3 1,000 350 30 210 50 50 10 1 15 1:3 I.W.L +35.0 I.W.L +20.0 Unit : m shore offing
WL1 WL2 WL3 Measurement of wave level
Height of incident wave Height of overlapping wave WL1 7.17 m 16.8 m WL2 17.1 m WL3 － 16.6 m
Soliton wave was confirmed for the first time in middle Japan Sea Earthquake in 1983.
Wave period: About 70 [s]
Wave for about ten a few seconds of cycle Breaking wave
wave force is very large
Soliton wave
Tsunami simulation in virtual coastal area
Numerical simulation using SPH
ICSE2012 20120829(Wed)-31(Fri)
(a)Moment that acts on breakwater
(b)Hydraulic gradient
into seabed soil
(c)Safety ration of Bearing capacity
1：2 I.W.L +20.0 5.0 Caisson-type Breakwater Rubble mound Seabed offing shore Unit : m PWP5 PWP6 PWP7 PWP8 PWP9 offing shore Unit : m R=15.0
Stability of the breakwater
against anaseism
Tsunami simulation in virtual coastal area
Numerical simulation using SPH
The breakwater will be
large deformation. The breakwater is moved due to the action of the initial impulsive wave force.
Shear deformation occurred in the rubble mound and the seabed soil and it receive seepage force, which decreased the stability. Especially, the decrease in the safety factor of the breakwater was larger when the excess pore water pressure in the ground was taken into consideration
Margin of bearing capacity＝ Bearing capacity strength － Tsunami force
－ Bearing capacity decrease in breakwater due to increase of excess pore
(a) (b) (c) 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 M om e nt t ha t a c ts on bre a kw a te r, M (M N ) 0 20 40 60 80 100 120 140 160 180 200 -1.0 -0.5 0.0 0.5 1.0 H yd ra ur ic g ra di e nt i n the g ro un d, igro u n d PWP5-PWP6 PWP7-PWP8 PWP6-PWP7 PWP8-PWP9 0 20 40 60 80 100 120 140 160 180 200 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 M a rgi n of be a ri ng c a pa c it y, (M N /m ) Duration time, t (s)
About excess pore water pressure Non-consideration
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Conclusion
ICSE2012 20120829(Wed)-31(Fri) Time Event d W d U P d H P d B P A 2 1, a a 3 a 4 a d W d U P d H P d B P d H P a R Sliding of the Breakwater Bearing capacity of the Breakwater Falling of the Breakwater
Wave pressure Excess pore water pressure
Seepage of the Seabed and Rubble
mound
Tsunami - Seabed soil – Breakwater interaction
The breakwater slid due to the action of the initial impulsive wave force.
Shear deformation occurred in the rubble mound and the seabed soil, which decreased the bearing capacity.
The hydraulic gradient increased in rubble mound and seabed soil at the shore side under breakwater due to seepage flow with the continuous wave pressure. The bearing capacity of breakwater decreased due to degradation of the ground caused due to the increment of excess pore water pressure in the seabed soil.
Conclusion
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Thank you
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Fluid, Fluid-Solid coupling
2D-Dambreak 3D-Dambreak
Tsunami hazard simulation (Hachinohe port)
Movie （Click fig.)
MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Margin of bearing capacity＝ Bearing capacity strength － Tsunami force
－ Bearing capacity decrease in breakwater due to increase of excess pore
1：2 I.W.L +20.0 5.0 Caisson-type Breakwater Rubble mound Seabed offing shore Unit : m PWP1 PWP2 PWP3 PWP4 PWP5 offing shore Unit : m R=15.0
Stability of the breakwater
against backrush
Tsunami simulation in virtual coastal area
Numerical simulation using SPH
(a) (b) (c) 0 20 40 60 80 100 120 140 160 180 200 0 2 4 6 8 10 M om e nt t ha t a c ts on b re a kw a te r, M (M N ) 0 20 40 60 80 100 120 140 160 180 200 -1.0 -0.5 0.0 0.5 1.0 H ydra uri c gra di e nt i n t he groun d, igro u n d PWP1-PWP2 PWP3-PWP4 PWP2-PWP3 PWP4-PWP5 0 20 40 60 80 100 120 140 160 180 200 -1.0 -0.5 0.0 0.5 1.0 M a rgi n of be a ri ng c a pa c it y, (M N /m ) Duration time, t (s)
About excess pore water pressure Non-consideration
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) 10 20 30 40 50 60 0 0.5 1 1.5 2 Duration time, t (s) S a fe ty r a ti o o f s li di ng , F s Analysis Theory 10 20 30 40 50 60 0 0.5 1 1.5 2 Duration time, t (s) S a fe ty r a ti o o f T ipp ing , F s Analysis Theory 10 20 30 40 50 60 0 0.5 1 1.5 Duration time, t (s) Fs Sliding Tipping Bearing capacity
Safety ratio of sliding
2 . 1 s F s d sU d B d a P a P a P W a1 2 3 4
d Bd sUd
s d W P P P f 2 . 1 s FSafety ratio of tipping
Safety ratio of sliding, tipping and bearing capacity
Numerical simulation using SPH
ICSE2012 20120829(Wed)-31(Fri)
津波越流力による
防波堤背後地盤の不安定化
撮影開始 2:30後 八戸港における津波来襲時の様子 出典: You TubeMAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) 320 112 9.6 67.2 16 3.2 1:3 W.L. +3.2 Unit : m shore offing Δh WL1 WL2 WL3 Measurement of wave level
B1 B2 B3 B4 B5 B6 A1 A2 A3 A4 A5 A6 C1 C2 C3 C4 C5 C6 D1 D2 D3 D4 D5 D6 E1 E2 E3 E4 E5 E6 F1 F2 F3 F4 F5 F6 G1 G2 G3 G4 G5 G6 H1 H2 H3 H4 H5 H6 I1 I2 I3 I4 I5 I6 J1 J2 J3 J4 J5 J6 K1 K2 K3 K4 K5 K6 Tsunami offing shore
: Measurement point of pressure
0 .6 4 1.6 Unit : m Caisson-type breakwater Rubble mound Circular slip surface analysis h0 = 1 .1 2 P1 P2
Case Offing site water level shore site water level Δh
Non-overflow 7.36 (m) 3.20 (m) + 3.20(m): Seabed + 0.96 (m) overflow 12.80(m) 3.20 (m) + 3.20(m): Seabed + 6.40 (m) 津波越流力による防波堤背後地盤の不安定化
津波流動場を想定した海岸域のモデル化
初期粒子間距離
：0.16m
粒子数
：10万個程度
防波堤
：不動剛体構造物
捨石マウンド
：不動透過性構造物
透水係数
k
m=1.0×10
-2m/s
（Dupuit-Forchheimer則）
海底床
：不透水性（境界）
海底地盤
：不動透過性構造物
透水係数
k
s=2.0×10
-5m/s
（Darcy則）
全 域 混成堤モデルICSE2012 20120829(Wed)-31(Fri)
防波堤越流時の津波挙動
津波越流力による防波堤背後地盤の不安定化
Movie （Click fig.)
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) 越流なし 越流あり
越流後の落下水塊による地盤内応力変化
-動水勾配の経時変化に着目した検討-
津波越流力による防波堤背後地盤の不安定化ICSE2012 20120829(Wed)-31(Fri) 越流あり t=16s 0.0 0.25 0.5 0.75 1.0 動水勾配（正は上向き） 越流水塊による急速載荷 W vimpact Impact force Seepage force Fu vshear Tractive force g v g Pimpact impact 2 2
防波堤背後地盤に作用する落下水塊の影響
津波越流力による防波堤背後地盤の不安定化 H1 Tsunami offing shore: Measurement point of pressure
0 .6 4 Unit : m Caisson-type breakwater Rubble mound Circular slip surface analysis h0 = 1 .1 2 P1 P2 H2 0 10 20 30 40 50 60 70 80 90 100 -40 -20 0 20 40 60 80 100 Duration time, t (s) Δ uH 2 -H 1 (kN ) 地盤表層と地盤内部の水圧差 ΔuH2-H1=ΔuH2-ΔuH1 zf R D W H 4 1 2 1 4 1 ~ g q zf R 乱流・渦に伴う乱れ 野口 他(1997): 津波遡上による護岸越流および前面洗 掘の大規模模型実験，海工論，第44巻，pp.296-300 土木学会刊(1999), 水理公式集 平成11年度版. 過剰間隙水圧，浸透力による土粒子の浮遊（液状化）
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) (a) 防波堤に作用する総モーメント力 (b) 支持力に対する安全率(地盤内過剰間隙水圧の考慮) 0 10 20 30 40 50 60 70 80 90 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Duration time, t (s) M om e nt t ha t a c ts on b re a kw a te r, M (M N ) Non overflow Overflow 0 10 20 30 40 50 60 70 80 90 100 -200.0 -150.0 -100.0 -50.0 0 50.0 100.0 150.0 200.0 M a rgi n of be a ri ng c a pa c it y, (kN /m ) Duration time, t (s)
No overflow : Wave force
No overflow : Wave force + EPWP Overflow : Wave force
Overflow : Wave force + EPWP
地盤の剛性低下を考慮した支持力破壊の検討
津波越流力による防波堤背後地盤の不安定化 offing shore Caisson-type breakwater Rubble mound Seabed ground A offing shore Caisson-type breakwater Rubble mound Seabed ground : Measurement point of pressure 地盤への津波力作用の影響により， 支持力強度が一層低下するICSE2012 20120829(Wed)-31(Fri) 有川太郎・佐藤昌治・下迫健一郎・富田孝史・辰巳大介・廉慶善・高橋研也(2012): 釜石湾口防波 健全な状態 津波来襲後 滑動に対する安全率
d d d H U B d d S P P P W f F ※（社）日本港湾協会：港湾の施設の技術上の基準・同解説（上）・（下），2007 d W d U P d H P Bd P Tsunami d W d B P d U P d H P ：堤体重量（kN/m） ：浮力（kN/m） ：揚圧力（kN/m） ：水平波力（kN/m） i a ：力の作用するアーム長(m) d f ：壁体底面と基礎との摩擦（=0.6）防波堤背後の水圧変動に伴う
防波堤の滑動に対する安全性低下
津波越流力による防波堤背後地盤の不安定化 有川ら（2012）による釜石湾口防波堤の被災検討 防波堤 港内側 港外側 津 波 ※一部加筆 2 2 2 2 2 2 2 2 1 2 1 2 1 2 2 h h h h h g h h g h g MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri)
防波堤背後の水圧変動に伴う
防波堤の滑動に対する安全性低下
津波越流力による防波堤背後地盤の不安定化 H1 Tsunami offing shore: Measurement point of pressure
0 .6 4 Unit : m Caisson-type breakwater Rubble mound Circular slip surface analysis h0 = 1 .1 2 P1 P2 H2 Increase in slide force Decrease in slide force
Decrease in backpressure with overflow
0.0 2.0 4.0 6.0 8.0 10.0 0.0 2.0 4.0 6.0 8.0 10.0 P2/ρgh0 P1 / ρ gh 0 Non overflow Overflow d W d U P d H P PBd Tsunami d H P d W d U P d H P PBd Tsunami d H P 要因② 渦等伴う 水圧変化 渦 度 要因① 水位変動に伴う 水圧変化 水位変動
ICSE2012 20120829(Wed)-31(Fri)
結 言
Time Event d W d U P d H P d B P A 2 1, a a 3 a 4 a d W d U P d H P d B P d H P a R Sliding Bearing capacity Falling Overflow Seepage failure vortex Reducedwater pressure Sliding
Scouring Bearing capacity Falling Liquefaction or Fluidization 越流による落下水塊による背後地盤への影響と防波堤の不安定化 地盤の洗掘・局所的液状化を誘発し、 支持力強度を低下させる 落下水塊の衝突力とその後のせん断流 乱流・渦に伴う乱れと圧力低下 滑動に対する安全性を低下させ、支持 力破壊と相まって防波堤が移動・転倒
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri) アンカーを用いた防波堤の固定による耐波強化 裏込カウンターによる耐波強化 消波ブロックによる耐波強化 我が国において
今後に対策として
ICSE2012 20120829(Wed)-31(Fri) aI=5.0m
R aP q W q W S c F Hd d d d d d d d s sin tan tan 1 sec tan ' 支持力に対する安全率 I p ga P 2.4
：谷本ら(1984) 津波外力 裏込めの抵抗力 d2 h1 h2 d1 d3 θ Ws 補強材： 割石の場合
Ws tan R
' tan tan 2 1 4 4 4 1 4 2 d h d d d d Ws s W ：最上層の被覆層を除いた滑り面より上の割石の水中重量 ：滑り面傾斜角（度） ： 1 2 tan 2：割石と割石の摩擦係数（=0.8） aI 1:2 8.7 15.0 5.0 1:1 Units : m すべり線 防波堤 捨石マウンド，割石 2 . 12 9.8 【kN/m3】 D c 【kN/m2】 D 【°】 海底地盤 35 ' 8.7 水中 単位体積重量 粘着力 内部摩擦角 45 0 0 － － 補強なし: 補強あり:08
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1
sF
55
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sF
滑動・転倒に対する効果も考えられる。 赤塚雄三,竹田英章,蓮見隆：混成堤の堤体背後に設置したコンクリート方塊あるいは 割石の滑動抵抗,第22回海岸工学講演会論文集,Vol.2,pp.421-425,1975.支持力補強（裏込め）
菊池喜昭,新舎博,河村健輔，江口信也：裏込めを有するケーソン式混成堤の安定性 の検討,土木学会論文集C（地圏工学）,Vol.67, No.4, pp.474-487,2011.MAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Tractive
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Movie （Click fig.)
MAEDA Lab. ICSE2012 20120829(Wed)-31(Fri)
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表層部に作用する 掃流力 内部応力変化に伴う浸透力 掃流力・馬蹄渦 内部応力変化 に伴う浸透力 落下水塊による 衝撃力 護岸（舗装）被害 防波堤被害 防潮堤被害結言 ～其の2：地盤工学における新たな課題～
地震動
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Weight：W
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Close upExcess pore
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e Weight：W Lift force：LF Tractive force ：τ Soil particle friction：Fr Close up Weight：W Lift force：LF Tractive force ：τ friction：Fr Close up Excess pore water pressure：ueMAEDA Lab.
ICSE2012 20120829(Wed)-31(Fri)
Tsunami experiment
using
centrifuge device
Numerical Analysis
using
SPH method
i h 粒子（質点） 影響半径 ゲート 300rpm 海底地盤 ケーソン式 防波堤 捨石 マウンド NG Superposition of smoothed physical valuesSmoothed physical values by using smoothed function for each particle
x
Limited zone of influence x1
x2 o Particle : i Particle : j rij xi xj κhi hi 防波堤の滑動 マウンド・地盤のせん断変形 捨石・地盤の噴出 防波堤 捨石マウンド 海底地盤 円弧 すべり解析 0 50 100 [%]
