381

東北地方太平洋沖地震における火山灰質盛土被害の分析

大塚　悟 1， 小石　悠介 2，磯部　公一 3，遠藤　真哉 4

1 長岡技術科学大学大学院　環境社会基盤工学専攻

2 東海旅客鉄道株式会社

3 北海道大学大学院工学研究院　環境フィールド工学部門

4 新和設計株式会社

原稿受理日：2015年2月9日，採用決定日：2015 年8月18日

地盤工学ジャーナル　Vol.10，No.3，381-390

Vol.?, No.?, ???-???

1

東北地方太平洋沖地震における火山灰質盛土被害の分析

1 2 3 4 1 2 3 4

概 要

p’=100 kPa

1. はじめに 2011 3 11

16%70%

1)

2)

3)~10)

11)

2. 福島県会津若松市一箕中学校周辺の地震被害

2.1 概要 2011 3 11 14 46 24 km

M9.012) 76

51

382

大塚・他

2

3 16

1

2.2 被災箇所

13)

1

2

尾根（丘陵地）

谷地形(谷幅50m) 被災箇所

支沢

支沢

N

1

N

地すべりブロック

主崩壊

0 20m 2

2.3 ボーリング調査結果 3

3 8 mN 1~2

4

N10~15 2 m 1~5

20 cm

3

4 13)

2.4 盛土材の地質

5 14)

●ボーリング地点

383

火山灰質盛土の被害 Vol.?, No.?, ???-???

3

20 km

2

50 cm

1 m

20~30 m

5 14)

2

3. 三軸圧縮試験による粒子破砕特性とせん断強度特性の把握

3.1 粒子破砕率の定量化

15) 6 Marsal

BM (1)

ΔFc (2)

MarsalBM

ΔFc 2

iM PB Δ∑= (1)

cicfc FFF −=Δ (2)

6 16)

3.2 福島現地採取砂の物理特性 7

21.4% 73.7% 4.9%15~20 mm

1

2 mm2 mm 2 mm

2.542 g/cm3

6.5710.9%

384

大塚・他

4

0

20

40

60

80

100

0.01 0.1 1 10 100

clay/silt sand gravel

Grain Size [mm]

Perc

ent p

assi

ng [%

]

7

1

ρs [g/cm3] 2.542 2.640 ρdmax [g/cm3] 1.659 1.645 ρdmin [g/cm3] 0.831 1.335

D50 [mm] 0.33 0.18 Uc 6.57 1.60 Fc [%] 10.9 0.0

3.3 試験条件 5 cm

10 cm2 mm

3

2~460% Dr = 60%

Dr = 80% Dr = 30%

3.4 等方圧密試験結果

3t 17) 8 BM

p’ = 100 kPa BM

p’ = 100 kPaBM

9 ΔFc

8 p’ = 100 kPaΔFc

p’ = 100 kPa

2 Dr

[%] p’

[kPa]

[kPa]

30 20

100

100 600

60 50 200

80 100 600

3 Dr

[%] p0’ [kPa]

[kPa]

[%/min]

60

20

100 0.1

35 50 100 200 300

4

Dr

[%] p0’ [kPa]

[kPa]

σd/2σ’0

60

50

100

0.12 0.16 0.18

200 0.11 0.14 0.17

0

10

20

30

40

0 200 400 600 800

Dr=30%Dr=60%Dr=80%

Mean effective stress p' [kPa]

Mar

sal's

bre

akag

e in

dex B M

[%]

8 BM

385

火山灰質盛土の被害 Vol.?, No.?, ???-???

5

0

10

20

30

40

0 200 400 600 800

Dr=30%

Dr=60%

Dr=80%

Mean effective stress p' [kPa]

Incr

emen

t of f

ines

con

tent

ΔF c

[%]

9 ΔFc

3.5 非排水せん断試験結果

10

p0’BM

ΔFc

p0’ = 100 kPaBM

ΔFc

ΔFc

BM

3) 11 q/p0’

p’/p0’ p0’q/p0’

12 15% q-εa

0

10

20

30

40

0

10

20

30

40

50

0 100 200 300 400

Marsal's breakage index BM

Increment of fines content ΔFc

Shear resistance angle φ'

Shear resistance angle φ ' [deg]

Initial mean effective stress p0' [kPa]

B M , ΔF c

[%]

10

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0

p0'=20kPa

p0'=35kPa

p0'=50kPa

p0'=100kPa

p0'=200kPa

p0'=300kPa

Nor

mal

ized

dev

iato

r stre

ss q

/ p'

0

Normalized mean effective stress p' / p'0

11

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 5 10 15 20

p0'=20kPa

p0'=35kPa

p0'=50kPa

p0'=100kPa

p0'=200kPa

p0'=300kPa

Nor

mal

ized

dev

iato

r stre

ss q

/ q ε

a=15

%Axial strain ε

a [%]

12 15% q-εa

3.6 繰返し三軸試験結果

13

p’ = 87 kPaDA = 5% 20

p0’ 50 kPa0.168 200 kPa 0.151 p0’ = 200 kPa

14

BM p0’ = 200 kPa p0’ = 50 kPa5%ΔFc p0’ = 200 kPa p0’ = 50 kPa 1%

0.00

0.05

0.10

0.15

0.20

0.25

0.30

1 10 100

p0'=50kPa

p0'=87kPa

p0'=200kPa

Cyc

lic st

ress

ratio

σd//

2σ0

Number of cycles Nc

Nc =

20

13 DA = 5%

386

大塚・他

6

05

10152025303540

0 50 100 150 200 250 300

Marsal's breakage index BM

Increment of fines content ΔFc

Initial mean effective stress p0' [kPa]

5 %

1 %

B M , ΔF c

[%]

14

3.7 試験の違いによる粒子破砕の比較

Dr = 60%

15 BM

p0’ = 100 kPaBM

3

BM 2~3%

16 ΔFc

BM p0’ = 100 kPaΔFc

ΔFc

BM 17 BM

ΔFc qBM

ΔFc BM

18 BM

ΔFc

σd BM

ΔFc

σd 20~60 kPaBM ΔFc

σd

0

10

20

30

40

0 100 200 300 400

Isotropic consolidation test

Undrained triaxial test

Cyclic triaxial test

Mar

sal's

bre

akag

e in

dex B M

[%]

Initial mean effective stress p0' [kPa]

15 BM

0

10

20

30

40

0 100 200 300 400

Isotropic consolidation testUndrained triaxial testCyclic triaxial test

Incr

emen

t of f

ines

con

tent

ΔF c

[%]

Initial mean effective stress p0' [kPa]

16 ΔFc

0

5

10

15

20

0 50 100 150 200

Marsal's breakage index BM

Increment of fines content ΔFc

Deviator stress q [kPa]

B M , ΔF c

[%]

17

0

5

10

15

20

0 20 40 60 80 100

Marsal's breakage index BM

Increment of fines content ΔFc

Half amplitude of cyclic shear stress ratio σd  [kPa]

B M , Δ

F c [%]

18

387

火山灰質盛土の被害

Vol.?, No.?, ???-???

7

4. 地震時変形解析による検討 4.1 概説

Newmark 18) Power SSANewmark

4.2 被害断面図

19

201.3 m 20

N

p’ = 87 kPa

19

1.761 m 14.674 m

4.402 m

2.348 m

0.587 m7.630 m

0.293 m 8.217 m

①

③

②

20

4.3 繰返し三軸試験結果を用いた残留強度の算出

c’ φ’20

DA = 5%

DA = 5%

20 DA = 5%

13 p0’ = 5087 200 kPa

σd

c’ φ’ 21c’ = 0 kPa φ’ = 18.0

4.4 入力地震動の設定

K-net19) 2011 3 11 14 47 14

5 km 22NS EWNS NS 4.51 m/s2

300

0

50

100

150

0 50 100 150 200 250 300

p'=50kPap'=87kPap'=200kPa

Normal stress σ [kPa]

c'= 0 [kPa]φ '= 18 [deg]

Shea

r Stre

ss τ

[kPa

]

21

-6

-4

-2

0

2

4

6

0 50 100 150 200 250 300Time [sec]

Acc

eler

atio

n [m

/s2 ]

22 NS

4.5 解析条件

5 20)

4.3

現況断面：崩壊後

（青）

原型断面：崩壊前

（赤）

地下水位

388

大塚・他

8

6 Dr = 60%

4.6 解析結果

23

1.38 m6 p0’ = 100 kPa

45.3 1.45 m87 kPa p0’ = 100

kPa

24

BM

ΔFc

BM

ΔFc

5. 結論

(1) p’ = 100 kPa

(2) p’ = 87 kPa

(3)

(4)

5 φ ’ [ ] 41.6 50.0

c’ [kPa] 0.0 φ ’ [ ] 18.0

c’ [kPa] 0.0 γt [kN/m3] 15.8

γsat [kN/m3] 17.9

6

p0’ [kPa]

φ ’ [ ] 20 50.0 35 47.5 50 46.3 100 45.3 200 42.7 300 41.6

0.0

0.5

1.0

1.5

2.0

0 50 100 150 200 250 300

φ' = 50.0φ' = 47.5φ' = 46.3φ' = 45.3φ' = 42.7φ' = 41.6実変位量

Cum

ulat

ive

disp

lace

men

t [m

]

Time [sec]

実測値1.38 m

23

Shear resistance angle φ ' [deg]

05

10152025303540

-0.5

0.0

0.5

1.0

1.5

2.0

4045505560

Marsal's breakage index BM

Increment of fines content ΔFc

Cumulative displacement

Cum

ulative displacement [m

]

B M , ΔF c

[%]

24

参 考 文 献

1) 42 5

pp.286-293 2001 2)

Vol.48 No.10 pp.3-6 2000 3)

No.757/ -66 pp.221-234 2002 4)

No.561/ -38

389

火山灰質盛土の被害

Vol.?, No.?, ???-???

9

pp.257-269 1997 5)

No.547/-36 pp.159-170 1996

6) No.554/

-37 pp.197-209 1996 7)

No.694/-57 pp.305-317 2001

8) 3.

Vol.53 No.11 pp.37-44 2005 9)

No.547/ -36 pp.221-229 1996 10)

44pp.701-702 2009

11) pp.27-64 2010

12) 133 2012 http://www.jma.go.jp/jma/kishou/books/gizyutu/133/gizyutu_133

.html 13)

47pp.1641-1642 2012

14) 5 1606

pp.50-56 2004 15)

35 3 pp.139-1421995

16) 44

3 pp.139-142 2003 17) p.665

2009 18)

32 pp.1895-1896 1997

19) K-nethttp://www.kyoshin.bosai.go.jp/kyoshin/

20)

48 pp.473-474 2013

(2015.2.9　受付）

390

大塚・他

Damage analysis of volcanic ash embankment collapse in The 2011 off the Pacific coast of Tohoku Earthquake

Satoru OHTSUKA1, Yusuke KOISHI2, Koichi ISOBE3 and Shinya ENDO4

1 Department of Civil and Environmental Engineering, Nagaoka University of Technology

2 Central Japan Railway Company

3 Graduate School of Engineering, Hokkaido University

4 Shinwasekkei Co. Ltd.

10

Damage analysis of volcanic ash embankment collapse in The 2011 off the Pacific

coast of Tohoku Earthquake

Satoru OHTSUKA 1, Yusuke KOISHI 2, Koichi ISOBE 3 and Shinya ENDO 4 1 Department of Civil and Environmental Engineering, Nagaoka University of Technology 2 Central Japan Railway Company 3 Graduate School of Engineering, Hokkaido University 4 Shinwasekkei Co. Ltd

Abstract A large-scale slope failure of embankment, which consists of volcanic sediment, at Aizu-Wakamatsu City in Fukushima Prefecture occurred due to The 2011 off the Pacific coast of Tohoku Earthquake. Some signatures of liquefaction have been observed in the collapsed embankment. When investigating the embankment slope failure mechanism, it is necessary to study the effects of particle breakage. In this study, some static and repeated triaxial tests were conducted for the soil material sampled from the site in order to investigate the change of the particle size distribution with isotropic consolidation stress and shear stress and the effect on the shear strength characteristics due to the particle breakage. From the test results, it was revealed that the sampled soil, subjected to the effective isotropic consolidation stress of 100kPa or less, increases the particle breakage amount rapidly and the shear resistance angle is significantly reduced with the increase of the particle breakage amount. Subsequently, seismic deformation analysis was carried out for the slope failure of the embankment based on the mechanical properties obtained in the test. As a result, a reasonable analysis result was obtained by considering the calculated residual strength based on the liquefaction strength curve and the reduction characteristics of shear resistance angle due to particle breakage. Key words: volcanic sediment, particle breakage, liquefaction, triaxial compression test, Newmark’s method