Ikuo Towhata

Geotechnical damage
caused by the recent gigantic
earthquake in Japan
Download an article from the site ofApril Issue, Bulletin, ISSMGE
Ikuo Towhata
University of Tokyo
Presentation at 3rd INTERNATIONAL CONFERENCE ON
GEOTECHNICAL ENGINEERING FOR DISASTER MITIGATION AND
REHABILITATION (GEDMAR) in Semarang, Indonesia

Features of the earthquake• Time of occurrence: 14:46 Local time on
March 11, 2011
• Magnitude of earthquake (JMA scale) = 9.0• Size of fault rupture : 500km * 200km• Death toll : not finalized. Probably over25,0001

Ikuo Towhata

Rupture zone

Previous
earthquake ofsimilar scaleand area
occurred inAD 869.

On earthquake motion

2

Ikuo Towhata

Acceleration records in Sendai City

Special feature of the damage• The affected area was vast.
• Number of damage was huge; e.g. nearly
2000 damages in river levees• Damages affected each other and madethe entire effects more significant: delay
and difficulty in emergency action andrestoration.
• LARGE-AREA and HUGE NUMBER OFDAMAGE

3

Ikuo Towhata

I have visited the following places: □TectonicmovementUplift of morethan 4.5m
Subsidence ofmore than 2m insea floor
Subsidence ofcoast was max.
1.2m

After Nikkei Science Magazine

4

Ikuo Towhata

Coseismic subsidence in coastal area

Photos by Mr. Daiken Suzuki, former master student, Univ. Tokyo

Ground level is lower than before;
Difficulty in drainage
Risk of flooding in typhoon season5

Ikuo Towhata

Coseismic subsidence during past earthquakes
Valdivia 1960, Chile、Kohchi, 1946, Japan,
1999 Izmit Bay, Turkey, 1964 Alaska

Later, ground came up.

Tectonic motion of coast after March 11
Near Sendai City, ground is coming up
but very slowly

March 110.5m subsidence

May 116

Ikuo Towhata

Building damage was minor

Intact buildings indowntown Sendai

No damage in Tsukidate
town in spite of nearly
3000 Gal and seismic
intensity=7

Types of geotechnical damage• Liquefaction in young sandy deposits• Lifeline• Embankment: road and levees• Failure of residential development fills

Note: the large number of damage in eachcategory above
made restoration very
difficult or still impossible.

7

Ikuo Towhata

Liquefaction in young sandy deposit(Urayasu City near Tokyo)

Feature of earthquake motion in Tokyo Bay area
Magnitude = 9.0; Long duration of shaking and many
number of cyclic shear; liquefaction easy to occur.
NS acceleration

K-NET NSmotion inUrayasu;
unliquefied site

Time (second)8

Ikuo Towhata

Liquefaction in residential area (Urayasu City)
Financial support is desperately needed forrestoration

House tilting in Chiba City9Ikuo Towhata

Liquefaction affected houses atmany places

Itako City NE of Tokyo

Differential subsidence around pilesupported building and disconnection oflifeline (Urayasu City)

10

Ikuo Towhata

Original topography of Itako City\ \ S oil07\user\geopdf\img-412004523\img-412004523-0001.jpg(Present airphoto)
Sand bar

Reclamation and fill

Natural lavee

Surface geology(1928年の旧地形図)¾ Used to be a small lake 100 yearsago¾ Reclaimed in 1977 already

Liquefaction occurred within thisformer lake

Successful soil improvement;
Sand compaction piles and gravel drains11

Ikuo Towhata

Lifeline damage

Floating of sewage
manhole caused byliquefaction ofground and backfill

Sewage pipelines were destroyed at
extremely many places

12

Ikuo Towhata

Liquefaction in former swamp;
not indicated in liquefaction hazard map:
public dispute

Ignorance of old
topography and too
much reliance on bore
hole database

Problems of river levees
Nearly 2000 sites of damage

Liquefaction in foundation, subsidence, and lateral spread

13

Ikuo Towhata

Sand boiling on river side

Liquefaction in foundation

14

Ikuo Towhata

Sliding inside levee body.
Foundation was intact.

Lateral spread as well, but no evidence ofliquefaction

Split laterally andsubsidence by1.8m

15

Ikuo Towhata

Repeated liquefaction; 4th time1978 main and aftershocks, 2003 and 2011

Most damages in river levees wereassociated with liquefaction infoundation or inside the levee.
Liquefaction is repeatable.

16

Ikuo Towhata

Tsunami effects
From sea to land

Heavy erosion and scouring behind sea walls Æ Walls
were lost upon the first tsunami attacks Æ No more
protection during the following tsunamis

Total demolition

17

Ikuo Towhata

Tsunami debris block transportation

Situation was made worse by tectonic
subsidence: insufficient levee height18

Ikuo TowhataQuick restoration of earth structure

Expressway was restored quickly as well:importance of transportation route19

Ikuo Towhata

Damage in residential development
in hilly area: cut and fill construction

Site of previous slope failure in 1978

In Sendai City,
there aremany
residential
developments
in hill areas:

20

Ikuo Towhata

In Sendai City: On Fill,21

Ikuo Towhata

On cut part, in contrast, damage ismuch less

Problems in residential fills• Requirement for cutting cost
• Original surface (soft) soil
remaining at the bottom• Soil filling without removingvegetation• Consequently, formation ofsoft layer between original
ground and fill22

Ikuo Towhata

Breaching of Fujinuma (irrigation) Dam

First dam was eroded and 150万m3 ofwater attacked a downstream village

23

Ikuo Towhata

Distortion of second dam; quickdraw-down effect? No overtopping

Flooded channel

24

Ikuo Towhata

8 victims in this village

Failure was rare in natural slope.
Exception:

Long-distance flow

25

Ikuo Towhata

Consideration on performance-based design

Summary• Vast area was affected and many damage
occurred.
• Liquefaction affected private houses• Residential development was damaged• People need help from geotechnicaldiscipline• Individual damage is not so serious but
number is significant.
• Should we revise design codes?

26