Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

LIQUEFACTION-INDUCED DAMADE TO BUILDINGSIN URAYASU CITY
DURING THE 2011 TOHOKU PACIFIC EATHQUAKE

Kohji TOKIMATSU1, Kota KATSUMATA2
1

Professor, Tokyo Institute of Technology, Tokyo, Japankohji@o.cc.titech.ac.jp
2
Graduate Student, Ditto
katsumata.k.aa@m.titech.ac.jp

ABSTRACT: An overview of the liquefaction-induced damage to buildings in Urayasu
city during the 2011 Tohoku Pacific earthquake is presented, based on fieldreconnaissance made after the quake. It is shown that extensive soil liquefaction occurredin most of the areas reclaimed after 1968, accompanied by numerous sand boils and large
ground settlement up to 60 cm as well as settlement/tilting of wooden and reinforced
concrete buildings supported on spread foundations. The extent and distribution of thedamage were significantly affected by local soil conditions including the thickness ofreclaimed fills, the depth to the bedrock or natural site period, and whether remedial
measures were taken against soil liquefaction, as well as structure soil structureinteraction effects.
Key Words: Tohoku Pacific earthquake, soil liquefaction, ground settlement, tilting andsettlement of building

INTRODUCTION
The “11th March 2011 Tohoku Pacific Earthquake” (M9.0) triggered an unprecedented tsunami, that
overwhelmed many towns and swept away several tens of thousands of houses and other buildings
along the coastline of northeast Japan, leaving about 20,000 people dead or missing. This earthquake
also caused extensive ground problems including soil liquefaction, leading to extensive damage tobuildings and infrastructures including roads, bridges, railways and ports, as well as to lifelines1),4).
Such liquefaction-induced damage was particularly significant in the city of Urayasu, affecting morethan 9,000 private houses. This paper reports on liquefaction-induced damage to buildings in the city.

665

GOELOGICAL AND GEOPHSICAL SETTING
Figure 1 shows a map of Urayasu city, Chiba Prefecture, with the years when reclamation work

Fig. 2

Fig. 1 Map showing Urayasu city withreclamation year4),5)

Map showing elevation in 2006

was done for each area. The city consists of three towns, Moto-machi, Naka-machi and Shin-machi.
The later two towns were in turns reclaimed after 1964 outside levees along the old coastline of theMoto-machi area. In the Naka-machi areas reclaimed in the first phase of the project through 1975,
many houses, commercial buildings and public facilities have been built. Meanwhile, the Shin-machi
areas completed in the second phase through 1980 have many high-rise condominium buildings,
universities, hotels and storehouses. Vacant lots still dot areas near the coast. Sand excavated from theseabed off Urayasu was mainly used to fill the reclamation sites. A magnitude-6.7 quake that occurred
off eastern Chiba Prefecture on Dec. 17, 1987 (Chibaken Toho-oki Earthquake), reportedly causedliquefaction in some parts of the city, including Kairaku 1-chome, Mihama 3-chome and Irifune
4-chome.
Figure 2 shows altitudes based on a digital elevation model with 2x2 m data spacing that wasdetermined with an airborne scanning laser survey made before the quake (December 2006). The
altitude is 0 to 2 meters north of the old coastline of 1964, 2 to 4 meters between the 1964 coastline
and the 1971 coastline to the south, and 3 to 7 meters in land reclaimed in or after 1979. The altitude isespecially high in a park near a coastal levee in Akemi.
Figure 3 shows depth distribution for the sedimentation of soft soils overlying the Pleistocene
deposit. Figure 4 is a cross section of the ground of Urayasu city along the A-A’ survey line in Figure
3. Hidden valleys of about 60 meters deep exist directly below Minato, Imagawa, Akemi and Irifune
areas, causing complicated changes in the thickness of soft clayey deposit in those areas. It can also beseen by comparing Figures 3 and 4 that the depth of Pleistocene deposit (Ds), with N-values of 50 orFig. 4

Fig. 3 Map showing thickness of soft soil
overlying Pleistocene deposit6),7)

666

Geological cross section along A-A’4)

greater, along the A-A’ line (northwest to
southeast) is about 20 meters below the sea levelnear the old coastline on the north side, andabout 50 meters below the sea level in the area
closest to the sea, showing that the depth
becomes greater toward the sea (in the southeast
direction). By comparison, along the northeast to
southwest line, which is perpendicular to the
A-A’ line, the depth becomes greater in thesouthwest direction. Figures 3 and 4 shows thatreclaimed fills in the Naka-machi and
Shin-machi areas are mostly deposited between
the sea level and a depth of 4-8 meters.
Figure 5 shows the distribution of H/Vspectral peak period in the city. The H/V peak
period varies significantly from 0.7s to 2.5s
within the city in such a way that it becomes
longer with increasing thickness of soft soil.

Fig. 5Map showing H/V spectral peak period

STRONG MOTION CHARACTERISTICS
Among the K-NET strong motion stations in and around Urayasu city along the Tokyo Bay coastat which digitized time-history data of the main shock are available (National Research Institute for
Earth Science and Disaster Prevention, 2011), soil liquefaction was observed near two stations: at
K-NET Inage (CHB024) and K-NET Tatsumi (TKY017). No liquefaction was spotted in theneighborhood of K-NET Urayasu (CHB008), which is located north of the old coastline in Urayasu
city.
The acceleration time history at K-NET Inage (a duration of 100 seconds including principal

Fig. 6 Acceleration time histories at K-NET
Inage during the main shock4)

Fig. 7

Fig. 8 Acceleration time histories at K-NET
Urayasu during the main shock4)

Normalized running spectra at Inage4)

Fig. 9667

Normalized running spectra at Urayasu4)

Fig. 10 PGA recorded in the city during
the main shock

Fig. 11 PGV recorded in the city during
the main shock

motions) is shown in Figure 6. The peak acceleration was 2.34m/s2 in the north-south direction and2.03m/s2 in the east-west direction. Spiky waves occurring around 120 seconds suggest a possibilityof cyclic mobility of sand in a liquefaction process. Figure 7 shows the running spectra at K-NET
Inage, normalized at the spectral peak of each 10-second interval. The periods become elongated from
0.7 s to about 4 s between 110 seconds to 140 seconds. This suggests that the ground liquefied
gradually with cyclic loading during the 30 seconds. Figures 8-9 present similar data for K-NET
Urayasu, where no liquefaction occurred. Unlike that at K-NET Inage, the running spectra at K-NET
Urayasu shows no apparent changes in the spectral peak period. Considering the fact that the principal
motion with accelerations greater than about 1 m/s2 at the non-liquefied Urayasu site lasted about 30 sfrom 110 to 140 seconds, complete liquefaction at Inage likely to have occurred in the latter part of theprincipal motion.
Figures 10 and 11 show the distribution of peak grand acceleration and velocity (PGA and PGV)
obtained with strong motion network operated by Keiyo Gas Co. Ltd (Urayasu city, 2012). Bothpeak ground acceleration and velocity varied in the city, with tendency where PGA is largest in the
Naka-machi area and PGV increases towards the sea.

LIQUEFACTION-INDUCED DAMAGE TO BUILDINGS
Figure 1 also shows with dotted line thearea within which our initial reconnaissancesurvey was made. The survey area covers not
only a part of the natural deposit on thenorthwest of the old coastline, including theneighborhood of Urayasu Station and K-NET
Urayasu site, but also most of the reclaimed
land in the city.
Based on the field performance of soils
and buildings including ground settlements aswell as settlements and tilting of houses, adamage distribution map was drawn in which
the extent of soil liquefaction is classified into
four categories (i.e., no, slight, moderate, andextensive) as shown in Fig. 12. It can be
confirmed that, liquefaction-induced damage
was not seen on the north of the old coastline

Fig. 12 Map showing extent of liquefaction
damage4)668

Photo 1

Sand boils stacked over the road

Photo 3 Buildings suffering large settlement
and tilting4)

Photo 2

Wooden house suffering large settlement

Photo 4 Buildings supported on pile (left) andspread (right) foundations4)

as of 1964 but was widely developed in the area reclaimed after that year. The areas that had
experienced liquefaction in the 1987 Chiba-ken Toho-oki Earthquake did re-liquefy. The degree ofdamage, however, varies from place to place within the reclaimed areas. In particular, some of thereclaimed zone escaped any liquefaction damage probably due to ground treatment including remedial
measures against soil liquefaction.
Our initial and follow-up reconnaissance survey including measurements of tilting angle anddirection of houses, partly using a 3D laser scanner, leads to the following findings.
1) In areas where liquefaction occurred, many sand boils (Photo 1), ground settlements up to 60
cm as well as settlements and tilts of building and houses on spread foundations (Photos 2-4) wereobserved everywhere. Vertical gaps were created around pile-supported structures due to groundsettlements (Photos 4-5), causing damage to piping and other facilities. Underground facilities, such as
manholes, emergency water tanks and parking lots were uplifted (Photo 6), damage was done to tap

Photo 5 Pile-supported buildings sufferinglarge ground settlement4)

Photo 6669

Uplifted underground parking garage4)

Fig. 13

Typical result of 3D laser scanning of buildings

water and sewerage systems, roads had dents
and utility poles were toppled. But little or no
damage to superstructures induced by seismic
force was observed.
2) Even where foundations settled or tilted,
few superstructures suffered damage. This was
because many buildings had adopted mat
foundations or highly rigid foundations toprevent damage to superstructures fromliquefaction or uneven settlings.
3) RC houses, and houses whose first floor
Fig. 14 Typical result of tilting angle andor semi-basement was made of reinforced
direction of houses in a district
concrete to prevent flood damage, sufferedlarger settlement, probably because their groundcontact pressure was greater.
4) When buildings face each other across a street, they tend to tilt backward, away from eachother, as in Photo 1 and Figures 13 and 14. When two buildings stand closely together, they often tilt
toward each other, as in Photo 3 and Figures 13 and 14. Such unique tendency was probably caused bybuilding-soil-building interaction effects in which the combined loads of the two adjacent buildings
increased their settlements on the neighboring side.
5) Several pile foundations, including some under construction during the main shock, suffered
severe damage probably due to permanent
lateral ground displacement caused by soilliquefaction.
6) In many areas located in the reclaimed
area but unaffected by soil liquefaction,
including the Tokyo Disneyland, ground
improvement work of some kind had been
carried out. This has confirmed theeffectiveness of ground improvement work
against the ground shaking with a peak groundacceleration of 2.0m/s2 caused by the M9 long
duration earthquake.
Figure 15 shows the distribution of
average inclination angle of residential houses
supported on spread foundations in eachFig. 15 Map showing distribution of average
district, based on the survey on about 9,000
inclination angle of houses7)
houses conducted by Urayasu city government.

670

Fig. 16 District by district distribution of inclination
angle of houses7)

Fig. 17 Map showing vertical groundsettlement between 2006 and 2011

Figure 16 summarizes the district-by-district
distribution of damaged houses in terms of
inclined angle. The figures show that thehouses located on the non-liquefied north side of
the old coastline had no damage, while thoselocated in the reclaimed area suffered extensive
damage. In particular, about 1/3-1/2 of thehouses in the residential areas of Maihama
3-chome, Benten 1-chome, Imagawa 1 to
3-chome, and Irifune 4-chome tilted more than
1/100.
These areas are classified in the
category of extensive damage in Figure 12.
Figure 17 shows ground subsidence
Fig. 18
Relation between average groundsettlement and average angle of inclination
estimated from the difference between thealtitudes obtained before and after the quake.
The ground in the liquefied area after the quake
has settled 0.2 to 0.4 m on the average, with smaller settlements on the roads. The value ofsubsidence reached as much as 0.6 to 0.8 m in some areas. It seems that the area with larger groundsettlements experienced more severe liquefaction damage to buildings.
Figure 18 shows the distribution of inclination angle of residential houses with respect to groundsubsidence. The figure apparently shows that the inclination angle tends to increase with increasingliquefaction-induced ground settlement. For example, houses titled more than 1/100 are about 10% if
the liquefaction-induced settlement (S) is less than 20 cm, whereas it becomes about 50% when S
becomes greater than 40 cm.

COMPARISON OF FIELD PERFORMANCE WITH SPT-BASEDLIQUEFACTION EVALUATION PROCEDURE
Figure 19 shows grain size distribution of boiled sand samples collected at several locations in
Urayasu. The samples each have high fine-grain content ratios, at 15 to 70 percent. Those fine grains
are believed to be non-plastic fine sand or silty sand, which correspond to the composition of the sandlayer in reclaimed land up to 10 meters below the sea level. This suggests that the reclaimed sand layerliquefied during the earthquake.
Figure 20 shows depth distributions of the N-value of earth filling or sand layers at each area of
Urayasu in gray. The average is shown in red. The data was obtained from the Chiba prefectural671

government2) and the authors’ own survey. For
the Akemi-Hinode area, separate graphs were
given for the northwestern and southeastern
districts, because the extent of the damage wasdistinctively different between them. It can beseen in the figure that the N-value in the sandlayer was extremely small in Tomioka,
Imagawa and Akemi-Hinode (northwest), butlarge in the neighborhood of Urayasu Station,
which is not reclaimed land, and in
Fig. 19 Grain size distribution curves of boiled sands4)
Akemi-Hinode (southeast), which is reclaimed
land but which is the highest in altitude. The
thickness of earth filling and sand layers was different from place to place, with Maihama,
Mihama-Irifune, Takasu and Akemi-Hinode marking high figures.
Comparison of these findings with liquefaction damage suggests the following:1) On the land side of the old coastline of 1964 or before, no liquefaction was observed eventhough the altitude is low and so the groundwater level is shallow. And in this area, the N-value ishigher than in recently reclaimed land where liquefaction occurred. These facts suggest a possibility
that “aging effect” of soil may have worked in mitigating liquefaction.
2) In Akemi-Hinode area (southeast), the N-value is relatively high and liquefaction damage wasminor. It could be surmised that differences in reclamation materials and method of reclamation may
have affected the degree of damage. Furthermore, the area’s altitude is rather high, indicating a
possibility that differences in altitude may have also affected the extent of damage. This may be
because, when the altitude is high, the groundwater level becomes relatively low and the consolidationof the silty sand layer below the groundwater table has progressed.
3) Comparison of Figures 8 and 13 shows that major liquefaction damage tended to occur just aboveor near buried valleys. Therefore, it cannot be denied that differences in ground surface response due
to differences in thickness of alluvial deposits could have affected the occurrence and extent of soilliquefaction.
Figure 21 are the results of liquefaction evaluation made with a method specified in theArchitectural Institute of Japan’s guidelines for basic structural design (2001), using the averageN-value for each area (Figure 20), a peak ground acceleration of 2.0m/s2 and at magnitude 9.0. The
ground water level is set at the average for each area, and the fines content was set at three different
levels—15%, 25% and 35%.

Fig. 20 Distribution of SPT-Value with depth at selected districts4)

Fig. 21 Result of SPT-based liquefaction evaluation at selected districts4)672

The FL-value (safety factor against
Table 1 Estimated and Observed Settlements inliquefaction) came to 1 or more at most depths
Urayasu4)
in the neighborhood of Urayasu Station, where
no liquefaction damage was observed, and in
the Akemi-Hinode (southeast) area, where
only minor damage was seen. But in otherplaces, the FL-value turned out to be lower
than 1. Especially in Mihama-Irifune, Takasu
and Akemi-Hinode (northwest), there are asequence of layers with the FL-value of lower
than 1 until the depth of nearly 20 meters.
These results agree with the actual damage
situation.
Table 1 shows comparison of the average
figure of estimated ground settlement based on
N-value distribution in each area in Figure 21(calculation made under the AIJ guidelines), and the actual, measurements. Because fine-grain content
ratio was not clear in many areas, estimates were made for 15%, 25% and 35%.
With fines content at 25%, the estimated settlement was 6 centimeters near Urayasu Station and 11
cm in Akemi-Hinode (southeast). But in other areas where liquefaction was severe, the estimate was
16 to 33 cm, with the highest figure for Akemi-Hinode (northwest). These estimates were generally inagreement with the tendency in actual figures. Even though a review is necessary after clarifying fines
content for each area and each depth, it can be said that the current design guidelines were able topredict, with a reasonable degree of accuracy, the possibility of liquefaction and degree of damage.

CONCLUSIONS
Field surveys on liquefaction-induced damage to buildings in Urayasu city during the 2011 Tohoku
Pacific Ocean Earthquake have found the following:1) Liquefaction occurred in areas reclaimed in relatively recent years. In some places, liquefaction
caused severe sand boils and ground settlement of up to 50 cm, leading to damage such as tilt andsettlement of wooden and reinforced concrete buildings with spread foundations, uplift of buried
structures and slumps of roads. Liquefaction also caused a major gap between pile-supported buildings
and surrounding ground, but no structural damage was observed in superstructures. Buildings with aspread foundation that had high rigidity, such as mat foundation, did not suffer structural damage totheir superstructures, even when they settled or tilted.
2) Degree of liquefaction differed from place to place even within the same city, and may depend onsuch factors as the thicknesses of reclaimed fill and alluvial deposit, the altitude or groundwater table,
and the presence of ground improvement, as well as the reclamation year, and the method and material
used for reclamation.
3) Some of boiled sand samples collected had high fines content, indicating that fine grained sands hadliquefied.
4) The currently available liquefaction evaluation procedure appeared to have performed well in
predicting the occurrence of soil liquefaction as well as the degree of resulting ground settlements. But
there is need to obtain more detailed data on ground and scrutinize the adequacy of those methods.

ACKNOWLEDGMENTS
This survey was conducted jointly with Prof. Shuji Tamura, Kyoto University, Prof. Hiroko Suzuki,
Tokyo institute of Technology, Dr. Eisuke Nishikawa, a researcher at the Tokyo Institute ofTechnology’s Global COE Program, Messrs. Youhao Zhou, Kodai Watanabe, Yoshiaki Ibaraki, Kei

673

Inamura, Yuki Takeda, Yusuke Nakano and Kazushi Tohyama, graduate students of Tokyo Institute ofTechnology, Dr. Akio Abe of Tokyo Soil Research Co. and the GEER team from the United States(Profs. Ross Boulanger, Scott Ashford, Jonathan Stewart, Kyle Rollins and Steve Kramer; and Dr.
Jennifer L. Donahue). Information regarding damage to building has been provided by Urayasu City.
We greatly appreciate their support and cooperation.

REFERENCES
1) Architectural Institute of Japan (2011): Preliminary reconnaissance report of the 2011
Tohoku-Chiho Taiheiyo-Oki earthquake (in Japanese).
2) Chiba Prefectural Environmental Research Center：http://www.pref.chiba.lg.jp/suiho/chishitsu.html(accessed 2011.10.27)
3) National Research Institute for Earth Science and Disaster Prevention (2011): Kyoshin Network
K-NET, http://www.k-net.bosai.go.jp/k-net/ (accessed 2011.10.27)
4) Tokimatsu, K., Tamura, S., Suzuki, H. and Katsumata, K. (2011): Damage to soils in the 2011
Tohoku Pacific earthquake, Research Reports on Earthquake Engineering, No. 118, 21-47 (inJapanese).
5) Urayasu City (2011a): Project of reclaimed land, http://www.city.urayasu.chiba.jp/menu2863.html(accessed 2011.10.27).
6) Urayasu City (2011b): Geographical and geological features of Urayasu city,
http://www.city.urayasu.chiba.jp/menu3185.html (accessed 2011.10.27).
7) Urayasu City (2012): Final report, Committee on investigation of remedial measures against soilliquefaction in Urayasu city.

674