Characteristics of Liquefaction in Tokyo Bay Area by the 2011 Great East Japan Earthquake

Soils and Foundations 2012;52(5):793–810

The Japanese Geotechnical Society

Soils and Foundations

www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf

Characteristics of liquefaction in Tokyo Bay area by the 2011 Great East Japan Earthquake

Susumu Yasudaa,n, Kenji Haradab, Keisuke Ishikawaa, Yoshiki Kanemaruc

aDepartment of Civil and Environmental Engineering, Tokyo Denki University, Japan bGeotechnical Department, Fudo Tetra Corporation, Japan cKyushu Branch, Kiso-jiban Consultants Co. Ltd., Japan

Received 17 January 2012; received in revised form 14 September 2012; accepted 14 October 2012 Available online 9 January 2013

Abstract

The 2011 Great East Japan Earthquake caused the severe liquefaction of reclaimed lands in the Tokyo Bay area, from Shinkiba in Tokyo through Urayasu, Ichikawa and Narashino Cities to Chiba City. However, the reclaimed lands that had been improved by the sand compaction pile method, the gravel drain method or other methods did not liquefy. The reclaimed lands that did liquefy had been constructed after around 1966 with soil dredged from the bottom of the bay. The dredged and filled soils were estimated to have been liquefied by the earthquake. Seismic intensities in the liquefied zones were not high, although the liquefied grounds were covered with boiled sand. Most likely it was the very long duration of the main shock, along with the large aftershock that hit 29 min later, which induced the severe liquefaction. Sidewalks and alleys buckled at several sites, probably due to a kind of sloshing around of the liquefied ground. Moreover, much sand boiled from the ground and the ground subsided significantly because the liquefied soil was very fine. Many houses settled notably and tilted. In Urayasu City, 3680 houses were more than partially destroyed. Sewage pipes meandered or were broken, their joints were extruded from the ground, and many manholes were horizontally sheared. This remarkable damage may also have occurred due to the sloshing around of the liquefied ground. & 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: Liquefaction; Reclaimed land; Earthquake; Sandy silt; Wood house; Sewage facilities (IGC: E08)

1. Introduction the northeast coast of Japan’s main island on March 11, 2011. The hypocentral region of this quake was about 500 km in The 2011 Great East Japan Earthquake, with a magnitude length and 200 km in width. The quake was followed by a of Mw¼9.0, occurred in the Paciﬁc Ocean about 130 km off huge tsunami that destroyed many cities and killed and injured many people along the Paciﬁc Coast. The numbers

n of dead and missing persons as of July 11, 2012 were 15,867 Corresponding author. and 2909, respectively. The tsunami broke the emergency E-mail addresses: [email protected] (S. Yasuda), [email protected] (K. Harada), cooling system of a nuclear power plant in Fukushima [email protected] (K. Ishikawa), Prefecture, and large areas of Japan have been plagued by [email protected] (Y. Kanemaru). radiation and a shortage of electricity ever since. In the Peer review under responsibility of The Japanese Geotechnical Society. geotechnical ﬁeld, many houses and lifelines were damaged by soil liquefaction, landslides occurred, dams failed and river dikes settled not only in the Tohoku district of northeastern Japan, but also in the Kanto district, which surrounds Tokyo.

0038-0806 & 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sandf.2012.11.004 794 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

very long duration of the main shock and of the aftershock, whichhit29minlater,ontheoccurrence of liquefaction and the associated damage to houses,isdiscussed.Remarkable phenomena, such as the buckling of sidewalks and damage to sewage facilities, due to a kind of sloshing around of the liqueﬁed ground, are cited, and the effectiveness of soil improvement in the prevention of liquefaction is discussed.

2. History and process of reclamation in the Tokyo Bay area

Tokyo Bay is a large eggplant-shaped bay facing the Pacific Ocean with a length of about 60 km and a width of about 20 km. Many mid-sized rivers, such as the Tama, the Sumida, the Ara and the Edo Rivers, flow into the bay, transporting soil from the surrounding mountains, 1000– 2000 m in height, to form deltas along Tokyo Bay. In 1603, the ruling shogun moved the capital of Japan from Kyoto to the area facing Tokyo Bay and named the new capital Edo. Edo was renamed Tokyo after a revolution in 1868. Reclamation of the coastal areas of Tokyo Bay started in the seventeenth century, after Edo became the capital, and accelerated after a revolution in the nineteenth century because of an increase in population. As illustrated in Fig. 2 (Endoh, 2004), the first reclamation areas consisted of the estuaries of the Sumida and the Ara Rivers in Tokyo and extended to Yokohama, the major port in the Tokyo Bay area. After the Second World War, a Fig. 1. Epicenter and rupture plane of the 2011 Great East Japan Earthquake (Partially quoted from Geospatial Information Authority of Japan). Ara River Sumida River Edo River Liquefaction occurred over a wide area of reclaimed lands Funabashi Chuo along Tokyo Bay, although the epicentral distance was very Koto Ichikawa Narashino large, about 380–400 km, as shown in Fig. 1. However, the Minato Tokyo Bay area was only about 110 km from the boundary Chiba of the rupture plane because the plane was very wide. Shinagawa Urayasu A great deal of land has been reclaimed in the Tokyo Bay Shinkiba Chiba- area since the seventeenth century. Liquefaction has been Ota port Tokyo- induced during past earthquakes, such as the 1923 Kanto Tokyo Bay port Earthquake and the 1987 Chibake-toho-oki Earthquake. Kawasaki However, the Great East Japan Earthquake is the first on Yokohama Tokyo Bay Aqua Line record to have caused liquefaction over such a wide area Ichihara and to have severely damaged houses, lifelines and roads. Yokohama Sodegaura After the Great East Japan Earthquake, many researchers -port started investigating the liquefied sites, the characteristic Kisarazu -port features of liquefaction, the soil conditions at the liquefied Kisarazu sites, the liquefaction-induced damage to structures, etc. Ishihara (2012) studied the soil conditions at liquefied sites Yokosuka -port in the Tokyo Bay area and in Itako and Kamisu, which Kimitsu Legend are north of the Tokyo Bay area and where very severe 㧦1985-1996 Kannon Futtsu 㧦1976-1985 liquefaction occurred. Tokimatsu and Katsumata (2012) Yokosuka -misaki 㧦1966-1975 Boso- conducted a detailed investigation of the damage to houses Miura 㧦1946-1965 in Urayasu City. Boulanger (2012) examined three aspects of Penisula 㧦1926-1945 the effects of the observed liquefaction on the strong ground 㧦1868-1925 㧦1603-1867 motions, buildings and a levee, and discussed how they 010km5 relate to current issues in geotechnical practice in the U.S. In this paper, several characteristic features of the liquefac- Fig. 2. History of reclamation in Tokyo Bay area (Slightly modified from tion in the Tokyo Bay area are presented. The effect of the Endoh (2004)). S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 795 very wide area along Tokyo Bay was reclaimed from drained of water with a pump, transported by a conveyor Kanagawa Prefecture to Chiba Prefecture through Tokyo pipe and then discharged from the pipe. As the dredged soil for industrial and residential purposes. contained a lot of water, coarse soil grains were probably As will be detailed later, a wide area from Shinkiba in deposited near the mouth of the conveyor pipe and fine soil Tokyo to Chiba City, through Urayasu, Ichikawa, Funaba- grains were probably deposited far from the mouth of the shi and Narashino Cities in Chiba Prefecture, was severely pipe. Moreover, the mouth of the pipe was re-positioned liquefied by the 2011 Great East Japan Earthquake. The often, resulting in very non-homogeneous strata. Photo 1 of reclaimed lands in this area were constructed after 1966, as the frontispieces shows an example of such very non- shown in Fig. 2. The history of the reclamation work in homogenous strata which contain many shells. Urayasu City, where serious damage to numerous houses After filling with the dredged soil and covering the soil occurred, is summarized in Fig. 3. Urayasu City is divided with hill sand, no soil improvement works have been into three towns, Motomachi, Nakamachi and Shinmachi, undertaken in Urayasu, except in several special areas, which literally mean old town, middle town and new town, such as the site of Tokyo Disneyland and several housing respectively. The ground of Motomachi formed naturally at lots where the sand compaction pile (SCP) method, the an estuary of the Edo River. On the contrary, the reclama- gravel drain (GD) method or other methods were applied tion of Areas A, B and C in Nakamachi began in 1965 to mitigate the risk of liquefaction. and that of Areas D, E and F in Shinmachi began in 1972. Theareaofeachzoneis1.0–3.5km2, and the total area of 3. Seismic intensity in the liquefied area Nakamachi and Shinmachi is 14.36 km2, which is about 75% of the total area of Urayasu City. According to an Fig. 5 shows the ground surface accelerations measured engineer who supervised the reclamation work in Urayasu, by K-NET (National Research Institute for Earth Science soil dredged from the bottom of the sea was filled to a and Disaster Prevention (NIED), 2011). The surface height of about sea level in the reclamation work. Then, accelerations did not reach the height of 160 cm/s2 to the filled surface was covered with hill sand transported 300 cm/s2. However, due to the giant-scale earthquake, the by boats from the Boso Peninsula. Fig. 4 is a schematic duration of the shaking was extremely long and the main drawing of the dredging work. Soil from the sea bottom just earthquake was followed by a strong short-interval after- outside Areas C, F and D was excavated with a cutter, shock, as will be characterized later.

Area 4. Identification of the liquefied zones A 2.18km2 Kairaku B 3.05km2 2 Mihama The authors started to investigate the Tokyo Bay area C 3.50km Total 8.73km2 the day after the earthquake, because all train service in the Higashino A area Reclaimed from 1965 Irifune Tokyo Bay area had been stopped immediately after the earthquake until midnight of the same day. The first place B area Hinode Benten visited was Urayasu City, which had experienced minor Akemi liquefaction during the 1987 Chibaken-toho-oki Earth- Tekkodori Takasu quake. In Urayasu, surprisingly, much water and sand D area Maihama had spewed out of everywhere and many houses had C area Minato settled and tilted, as shown in Photo 2 of the frontispieces. Area E area The next day, the authors rushed to Chiba City, which is Chidori D 2.42km2 E 2.21km2 about 20 km from Urayasu City, because an inhabitant 2 1km F 1.00km had reported to the authors that severe liquefaction had F area 2 Total 5.63km also occurred there, as shown in Photo 3 of the frontis- Reclaimed from 1972 pieces. According to this information, the authors esti- Fig. 3. Detail history of reclamation in Urayasu (Quoted from the report mated that liquefaction would occur over a very wide area by the Technical Committee organized by Urayasu City, (2012)). along Tokyo Bay, from Tokyo to Chiba City, although no news of liquefaction had been reported on TV or in the newspapers at that time. This is because all the news was

Pump dredger focused on the serious damage to houses and a nuclear Discharge pipe power plant due to the tsunami that hit. The authors then Distributing pipe Discharge decided to investigate the area where the liquefaction had Floating pipe Sea level opening likely occurred with many groups, including several stu- Pump Sea Cutter Sea bottom wall Reclaimed soil dents. In the investigation, the roads where boiled sand had been and had not been observed were marked on maps with red and blue lines, respectively, as shown in Fig. 6. Here, in this paper, the red and blue lines are indicated by Fig. 4. Schematic drawing of the dredging work. solid and broken lines, respectively. The zones surrounded 796 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

Gyoutoku[CHB029] Sunamachi[TKY013] Main:166.8 Gal Liquefied Main:169.2 Gal After:87.7 Gal Shiohama[TKY020] After:75.7 Gal Mihama A Non-Liquefied Main:152.5 Gal 4 After:77.1 Gal Inage[CHB024] Main:301.1 Gal Irifune After:Unpublished A A Tomioka 3 1 Urayasu[CHB008] Imagawa Tatsumi[TKY017] Main:174.3 Gal B Main:224.4 Gal After:82.3 Gal Benten 1 After:149.1 Gal B2 Chiba[CHB009] Maihama Main:187.1 Gal Tokyo After:80.6 Gal Disneyland 4000m

Fig. 5. Surface accelerations recorded by K-NET. A1 B2 Improved area 1km Test site by the red lines were judged to be liquefied, but some small Fig. 6. Method to judge liquefied and non-liquefied zones. (For inter- districts within the zones, for example, districts A1,A3, pretation of the references to colour in this figure the reader is referred to the web version of this article.) A4,B1 and B2, did not liquefy, because their grounds had been improved by sand compaction or other methods to be mentioned later. Thus, about ten days were necessary to that was liquefied in Christchurch during the 2011 investigate the whole area from Odaiba in Tokyo to Chiba Christchurch, New Zealand Earthquake. City through Urayasu, Ichikawa and Narashino Cities. (5) The epicentral distance of the liquefied area in Tokyo A tentative map of the liquefied zones was drawn based on Bay is very large, around 400 km. However, the this first stage investigation (Yasuda and Harada, 2011). distance from the boundary of the rupture plane is An investigation of the liquefied sites was also conducted only 110 km, because the rupture plane is very wide. by several JGS (Japanese Geotechnical Society) members (6) The farthest liquefied site was Minami-boso City on not only in the Tokyo Bay area, but also over a wide area the Boso Peninsula where the epicentral distance was in the Kanto district, because liquefaction had occurred at 440 km, as measured by Wakamatsu (2011). many sites, such as along the Tone River and in reclaimed lands along the coast of the Pacific Ocean. As the liquefaction-induced damage to houses, river dikes, roads, 5. Estimation of brief soil cross sections in liquefied areas lifelines and ports and harbors was serious, the Kanto from Tokyo to Chiba Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism decided to conduct Recently, in Japan, geotechnical data bases have been joint research with JGS to identify the liquefied sites. In prepared and published on the internet for many cities and August, the results of the joint research were published on prefectures. JGS (Japanese Geotechnical Society) also their Web site (http://www.ktr.mlit.go.jp/bousai/bou published geotechnical data bases for several districts sai00000061.html). Fig. 7 shows a map of the liquefied (Yasuda et al., 2010). Based on three sets of data bases zones, estimated thus far; it has been modified slightly for the liquefied areas, that had been published by JGS from the tentative map. The remarkable features of the (2010), the Chiba Prefectural Government (http://www.pref. liquefied zones are as follows: chiba.lg.jp/suiho/chishitsu.html) and the Tokyo Metro- politan Government (http://doboku.metro.tokyo.jp/start/ (1) The ground surface all around the reclaimed lands at 03-jyouhou/geo-web/00-index.html), the authors estimated Shinkiba in Tokyo, Urayasu City, Ichikawa City, the brief soil cross sections along 11 lines, which are Narashino City and western Chiba City was covered perpendicular to the shore lines (Yasuda and Hagiya, with boiled sand. Many houses, roads and lifelines 2011). Fig. 8(1) to (3) illustrate the estimated soil cross were severely damaged in the liquefied zones, as will be sections along three of the lines together with the zones mentioned later. The most serious damage was induced where sand boils were observed. in Urayasu City; namely, an area of about 85% of the One soil cross section, shown in Fig. 8(1), is the section city was liquefied. along line Urayasu 3–3 0 where many houses and lifelines (2) Sand boils were observed here and there on the reclaimed suffered very serious damage due to liquefaction. The lands at Odaiba, Shinonome, Tatsumi, Toyosu and zones where sand boils were observed coincide exactly SeishininTokyoandineasternChibaCity. with the areas of reclaimed land on the sea side from the (3) Liquefaction occurred at limited spots in Yokohama, old sea wall. In the reclaimed zone, a layer filled mainly Kawasaki and Kisarazu Cities, which are southwest with hill sand (B) and a layer filled with dredged sandy soil and southeast of Tokyo and Chiba City. (F) with low SPT N-values of 2–8 are deposited with a (4) The total liquefied area from Odaiba to Chiba City thickness of 6–9 m. An alluvial sand layer (AS), with reached about 41 km2, which is wider than the area SPT N-values of 10–20, underlies the filled layer with a S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 797

Horie Higashino Mihama Imagawa Takasu 33’2-chome 1-chome 3-chome 2-chome WL=-2.99m WL=-3.00m WL=-0.50m WL=-0.90m WL=-1.98m Level SPT-N SPT-N SPT-N Shinonome Seishin SPT-N SPT-N B (Tpm) 0.0 Funabashi 1’ F Tatsumi Takahama As -10.0 As -20.0 Takasu Shinkiba 3’ 2’ Dc Ac -30.0 Odaiba Liquefied zone Improved site in Tatsumi -40.0 2km (medical center building) Ac -50.0 Ds As Fig. 7. Liqueﬁed area from Odaiba in Tokyo to Chiba City (Joint -60.0 Old sea wall research by Kanto Regional Development Bureau of the Ministry of -70.0 Land, Infrastructure, Transport and Tourism and JGS). -80.0 0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0 Distance (m)

Boiled sand was observed thickness of 4–8 m. A very soft alluvial clay layer (Ac)is (1) Urayasu 3-3’line deposited under the AS layer with a thickness of 10–40 m, Higashi funabashi with an increasing thickness towards the sea. A diluvial 5-chome 11’WL=-11.65m (Pleistocene) dense sandy layer (Ds), with SPT N-values of SPT-N more than 50, underlies the alluvial clay layer. The water Yatsu Level 5-chome Yatsu (Tpm) Lm Takasecho WL=-2.75m 3-chome Takasecho Takasecho table is kept as shallow as the ground level (G.L.), 0.5 m 10.0 SPT-N WL=-1.85m WL=-0.65m WL=-1.30m WL=-1.00m SPT-N to 3 m, by decreasing the depth towards the sea. On the SPT-N SPT-N SPT-N B contrary, in the natural land which is inland from the old F 0.0 sea wall, the same A layer as in the reclaimed land is As S Ac deposited from the ground surface. If the AS layer had -10.0 liquefied, sand boils should have appeared in the natural Dc land. However, no sand boils, nor damage to houses or -20.0 Ds lifelines, occurred in the natural land. Therefore, it can be A -30.0 estimated that the S layer basically was not liquefied by the Old sea wall 2011 Great East Japan Earthquake, although some loose -40.0 parts of the reclaimed land may have liquefied and some 0.0 500.0 1000.0 1500.0 2000.0 2500.0 Distance (m) parts of the dredged sandy soil under the water table may Boiled sand was observed have liquefied. (2) Narashino 1-1’ line The composition of the soil layers is similar for the other Minami hanazono 10 soil cross sections, although the thickness of each layer 1-chome is different. In the cross section shown in Fig. 8(2), the Ac 2 2’ SPT-N Level layer is thin because this site is not a delta, but a seashore, Lm Kemigawacho Masago Isobe Isobe (TP m) with a behind-standing terrace under topographical con- 3-chome 5-chome 6-chome 8-chome 0 10.0 ditions. In the cross section of Mihama 2–2 , the AS layer WL=-1.80m WL=-1.50m WL=-0.10m WL=-1.35m SPT-N SPT-N SPT-N SPT-N is thicker than the other sections. However, the thickness B and the SPT N-values of the B and F layers and the depth F 0.0 of the water table in the reclaimed lands are similar for all As sections. -10.0 Ds 6. Detailed soil investigation and tests conducted after the -20.0 Dc earthquake Old sea wall -30.0 A detailed soil investigation and tests were begun several 0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 Distance (m) months after the earthquake by various organizations in Boiled sand was observed the Tokyo Bay area. Among them, a technical committee (3) Chiba Mihama 2-2’line organized by the Urayasu City Government and chaired by Prof. K. Ishihara carried out detailed soil investigations Fig. 8. Estimated brief soil cross sections. in the summer of 2011 by boring, SPT, CPT, PS logging, B: Fill, F: Dredged soil, As: Alluvial sand, Ac: Alluvial clay, Ds: Diluvial sand, Dc: Diluvial clay, Lm: Loam undisturbed sampling, cyclic triaxial tests and other methods at the locations plotted in Fig. 9, and reported valuable data in December 2011 (Urayasu City, 2012). In the first step, the unpublished boring data were The following is a brief summary quoted from the report collected and compiled in order to select additional by the Technical Committee. investigation sites. As 221 existing borings were found 798 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

New investigation Boring Boring and Sampling Boring and Piezo cone Piezo cone PS loggingNew

Existing data by Urayasu City Existing data by private companies Existing data by Chiba Prefecture

Fig. 11. Estimated thickness of the F layer under the water table (Quoted 0.0 1.0km from the report by the Technical Committee organized by Urayasu City (2012)) and the locations of the heaved roads and footways. Fig. 9. Existing and new soil investigation sites in Urayasu City (Quoted from the report by the Technical Committee organized by Urayasu City (2012)).

Severely damaged zone

Depth of the bottom of alluvial layers Shallower than T.P-20m T.P-20m to -30m T.P-30m to -40m T.P-40m to -50m T.P-50m to -60m T.P-60m to -70m T.P-70m to -80m

Fig. 10. Estimated depth of bottom of alluvial soil layers (Quoted from the report by the Technical Committee organized by Urayasu City (2012)). Fig. 12. Estimated depth of the water table (Quoted from the report by the Technical Committee organized by Urayasu City (2012)).

(plotted in Fig. 9), it was planned that 23 additional zones might have been very shallow before the reclama- borings with SPT, sampling, etc. and 53 CPT would be tion. In other words, it can be said that thick dredged soil conducted. Based on these data, contour lines of the depth is deposited in the southern zones of Nakamachi. The of the bottom of the alluvial layers, contour lines of the depth of the groundwater table is around G.L.1m to thickness of the dredged and the ﬁlled layers under the G.L. 2.5 m on average, as shown in Fig. 12. However, groundwater table and contour lines of the depth of several zones in Nakamachi are shallow at less than the groundwater table were estimated. The depth of the G.L.1 m. Groundwater tables are also shown in the soil bottom of the alluvial layers increases from 20 m in cross sections of Fig. 8 relative to T.P. (Tokyo Peil), which Motomachi to about 40 m in Shinmachi with several is the standard mean sea level of Tokyo Bay. In the zones narrow buried valleys up to 70 m in depth, as shown in where boiled sand was observed, the groundwater tables Fig. 10. The thickness of the F layer under the ground- are higher than the level of T.P.¼0 m, especially in water table is small at the boundary with Motomachi and Narashino and Chiba. Therefore, it can be said the increases toward the sea, as shown in Fig. 11. However groundwater level does not correspond to changes in the there are two remarkable belt zones where the F layer is tide level. Some small seasonal changes in the groundwater thin in the southern zones from the boundary between table, due to rain, may be included in the existing boring Nakamachi and Shinmachi. The sea bottom of these belt data, but it is impractical to adjust Fig. 12 for such S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 799 changes. The relationship between the depth of the existing and new boring data. Although line D-D0 in groundwater table and the damage to houses will be Fig. 13(2) is almost the same as line 3–3 0 in Fig. 8(1), the discussed later. depths of the soil layers are fairly different, because the new soil Fig. 13(1) and (2) shows soil cross sections crossing through cross section is estimated based on the old and new boring Motomachi, Nakamachi and Shinmachi estimated by the data. Notably, the following depths differ with the data source:

(a) The depth of the bottom of the Ac layer does not simply incline towards the center of Tokyo Bay, but has two valleys. The depth of the top of the DS layer is more complex, with several buried valleys. (b) There is a special layer, called the Nanagochi layer, which was deposited 10,000–20,000 years ago.

Frequency distributions of the normalized SPT N-values, N1, and the fines content, Fc,oftheF layer and the AS layer are compared in Fig. 14(1)–(4). Although layer F had to be liquefied, the fines content of layer F is very large, with an average value of about 44%, and very scattered from Fc¼0% to 100%. The average fines content of layer F is greater than that of layer AS,althoughlayerF was essentially taken from layer AS. According to the engineer who supervised the reclamation work in Urayasu, this difference must be attributed to the lack of alluvial sandy soil for the reclamation work. As the dredged zones were located just at the top of the delta formed by the Edo River, there was not enough sandy soil for the filling. Thus, some Fig. 13. Detailed soil cross sections (Quoted from the report by the alluvial clay had to be excavated and mixed with the alluvial Technical Committee organized by Urayasu City (2012)). sandy soil. Fig. 15 shows the relationships between Fc and

700 350 μ μ+σ (1) Dredged soils (2) Dredged soils 600 300 Average N1=5.46 Average FC=43.8% 500 (In log normal, 250 (In log normal, median is 3.46 and μ-σ μ median is 32.8 and 200 400 variance is 4.68) variance is 1.84) 300 150

200 100 Number of samples Number of samples 100 50

0 0 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 N1 FC (%)

350 350 μ-σ μ μ+ (3) Alluvial sands (4) Alluvial sands 300 300 Average F =30.9% Average N1=12.9 C 250 (In log normal, 250 (In log normal, μ-σ μ median is 21.6 and 200 median is 9.82 and 200 variance is 1.77) variance is 2.70) 150 150

100 100 Number of samples Number of samples 50 50

0 0 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 FC (%) N1 N σ σ 2 N1=170 /( v’+70), v’ Effective overburden pressure (kN/m )

Fig. 14. Frequency distributions of N1 and Fc for dredged soil and alluvial sand (Quoted from the report by the Technical Committee organized by Urayasu City (2012)). 800 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 plasticity index IP. Even though the data are scattered, layer are 0.25–0.30 and 0.30–0.40, respectively, although IP increases with Fc for both dredged and alluvial soils. the data are very scattered in the F layer. Therefore, it can In many Japanese design codes for liquefaction, for example, be said that the soils in the F layer are more liquefiable ‘‘Specification for Highway Bridges (Japan Road Association, than those in the AS layer. 2002)’’, fine soil with IPo15 is judged as liquefiable even though its Fc435%. According to this criterion, soil 7. Remarkable behavior of the ground due to liquefaction of Fco60%, such as the soil in Urayasu, is liquefiable. As shown in Fig. 14,theaverageSPTN1 of layer F is 5.46, lower 7.1. Process of the occurrence of liquefaction than the average N1 of layer AS, which is 12.9. Therefore, it can be said that the dredged soil is looser than the As the earthquake occurred at 14:46 in the afternoon on alluvial sand. Friday, many important photos and movies were taken at Table 1 compares the average N1, Fc and clay content Cc several sites along Tokyo Bay to study the process and the of the F layer tested before and about 5 months after the mechanism of liquefaction. Among them is a series of photos 2011 Great East Japan Earthquake at several sites. There taken by Mr. Katsunori Ogawa just after the earthquake at is almost no difference in the N1 values at depths of 0 m to Maihama 3-chome in Urayasu City. The photos are intro- 5 m, where dredged soil is deposited, as shown in the table. duced in Photo 4(1) to (12) of the frontispieces. The locations Undisturbed samples were taken at nine sites to obtain of these photos are shown on the map in Fig. 17.Thefollow- the cyclic shear strength and the shear modulus. A fixed ing are Mr. Ogawa’s comments on the photos Ogawa (2011): piston, thin-walled, stainless steel tube sampler with an oooShake due to main shock started at 14:47 in inner diameter of 75 mm and an outer diameter of 79 mm Urayasu444 was used for the sampling. The quality of the undisturbed samples was checked by comparing their shear moduli No. 1 o14:564: The spewing out of muddy water obtained from the two tests. Shear moduli G, at a low started in a northeast direction. It took several minutes strain level of g7106 by cyclic torsional tests, coincided to start the boiling after the settle of the main shock. fairly well with the shear moduli obtained by in situ PS No. 2 o14:564: Muddy water also began to spout in a logging. Therefore, it was judged that the test results southeast direction from the opening between a road obtained with the samples were reliable. Frequency dis- and residential lots. tributions of the shear stress ratio, to cause liquefaction in No. 3 o15:004: Same direction as No. 1. the 20 cycles tested by cyclic triaxial tests, RL (NL ¼20, No. 4 o15:004 In a southwest direction, muddy water DA¼5%) for the F and the AS layers, are shown in was boiling from the opening between a road and a Fig. 16. The dominant RL values for the F layer and the AS footway. No. 5 o15:014: Boiled muddy water gradually spread and covered the road. No. 6 o15:024: Muddy water spread, and finally covered flowerpots and reached the bottom of a car. P No. 7 o15:034: Much muddy water was spouting from side ditches and covered a road. Same direction as No. 1. No. 8 15:104: Muddy water was spouting with a Dredged soils o height of about 20 cm from the holes in a sewage manhole lid.

Plasticity Index, I Alluvial soils No. 9 o15:164: Much muddy water spewed out before the strong aftershock along the Miake River.

oooA strong aftershock hit Urayasu at 15:16444 Fines content, FC (%)

Fig. 15. Relationships between Fc and IP (Quoted from the report by the No. 10 o15:194: A footway heaved and houses Technical Committee organized by Urayasu City (2012)). settled along the Miake River.

Table 1

Comparison of N1 and Fc before and after the earthquake (Quoted from the report by the Technical Committee organized by Urayasu City).

Depth (m) Mean depth (m) Before earthquake After earthquake

N1 Fc (%) Cc (%) N1 Fc (%) Cc (%)

0 to 5 2.5 6.3 49.4 16.2 5.7 52.2 17.9 5 to 10 7.5 5.2 39.1 8.8 7.0 31.1 10.1 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 801

20 to 29 More than 10 to 19 min. 50 cm min. 40 to 49 cm =5%) =5%) 0.40 0.45 0.40 0.45 Immediately DA DA 10 to 14 after 30 to 39 cm 0 to 9 cm min. =20, =20, 0.35 0.40 0.35 0.40 L L 20 to 29 cm N N 5 to 9 min. 1 to 4 min. ( ( 10 to 19 cm L L R R 0.30 0.35 0.30 0.35

0.25 0.30 0.25 0.30 (1) Timing of boiling after main shock (2) Height of muddy water after main shock Shear stress ratio to cause Shear stress ratio to cause liquefaction liquefaction 024 0246 0 to 9 min. Went away Depends on Number of samples Number of samples site 10 to 19 (1) Dredged soils (2) Alluvial sands min. Untile after 20 to 29 shock Fig. 16. Frequency distributions of shear stress ratio to cause liquefaction. min. Covered

(3) Time of the stop of boiling (4) Surface water before aftershock

9 5 to 16 min. 10 More than 0 to 9cm 1 to 4 min. 50cm 11,12 Immedately Maihama Sta. 8 1,3,7 after 10 to 19cm 30 to 39cm 20 to 29 cm 4 2,5

(5) Timing of boiling after aftershock (6) Height of muddy water after aftershock

Fig. 18. Questionnaires to inhabitants of Irifune. 150m

Fig. 17. Locations of photos taken by Mr. K. Ogawa. 3 of the respondents and another 1/3 of them answered that the settlement of their houses was zero and 10–19 cm, No. 11 o15:214: The southwest road was completely respectively, after the main shock. And, many inhabitants covered with muddy water. The water pipes looked like noticed the settlement the next day. As shown in Fig. 18, they were going to break. the answers to each question were unique, even though the No. 12 o15:224: Many houses settled and tilted, and area was not wide. The reason for this is not clear, but it cars were submerged in the boiled muddy water. may be attributed to the non-uniformity of the dredged sand and the depth of the groundwater table. According to the series of photos and the questionnaires The authors sent out questionnaires to about 30 inha- filled out by the inhabitants, several interesting processes bitants in the Irifune district, which is also located in of liquefaction and boiling were found: Urayasu City, but about three km northeast of Maihama, to ask about the timing of the boiling and the height of the (1) The starting times of the boiling of muddy water were boiled muddy water. The answers are summarized in quite different depending on the site. This implies that Fig. 18. About 1/3 of the respondents had observed the the depths of the liquefied layer and/or the water table boiling of muddy water immediately after the main shock; are different at different sites. Although the answers to however, another 1/3 of them recognized the spout of the questionnaires from the inhabitants in the Imagawa muddy water 5–9 min after the main shock. Other district, which is between Maihama and Irifune, are not respondents found the muddy water at a different timing. introduced in this paper, some inhabitants testified that The height of the muddy water was not high, mainly less boiling did not occur during the main shock, but that it than 9 cm, after the main shock. About 2/3 of the occurred during the aftershock. The excess pore water respondents mentioned that the boiling of muddy water might have increased, but there was no liquefaction continued up to the aftershock, and about 3/4 of the during the main shock at this site. respondents watched the covered water until the after- (2) The boiling of muddy water was not intense after the shock. On the contrary, about 3/4 of the respondents main shock, such as oozing out; however, the boiling observed the spewing out of muddy water just after the accelerated during the aftershock. The increased water aftershock and the height of the water was apparently table after the main shock might have caused the greater than the height after the main shock. This means acceleration of the boiling during the aftershock. Or, a the boiling accelerated due to the aftershock and more fissure, induced in the ground during the main shock, severe liquefaction occurred at some sites during the might have accelerated the boiling during the aftershock. aftershock. The question on the timing of the settlement (3) Some of the houses settled during or immediately of houses must have been difficult to answer; however, a 1/ after the main shock, although others settled after the 802 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 ) 2 200 Liquefaction 100 Counter measures 0 GD -100 SD 30 -200 100 80 100 120 140 160 DM-J Drainage (1) CHB024:Inage, NS, 2011/03/11 14:46:16 (s) 40 130 ) Acceleration (cm/s 2 200 Solidification 210 Compaction SCP 100 DM-MM 560 450 0 170 -100 -200 TOFT Acceleration (cm/s SAVE 80 100 120 140 160 (2) CHB008:Urayasu, EW, 2011/03/11 14:46:15 (s) 110

Fig. 19. Comparison of accelerographs recorded at K-NET Inage and SCP : Vibratory Sand Compaction Pile method Urayasu. SAVE : Non-vibratory Sand Compaction Pile method DM-MM : Deep Mixing method (mechanical mixing) Horizontal buckling TOFT : Lattice type Deep Mixing method DM-J : Deep Mixing method (jetting) SD : Sand Drain method Wall Liquefied layer GD : Gravel Drain method A kind of sloshing Fig. 21. Proportion of ground improvement methods implemented in (1) Horizontal buckling at a boundary Tokyo Bay.

Horizontal acceleration, which was induced at about 118 s. buckling (14:48:13). On the contrary, the frequency changed to a low value after two peaks at 120 s. (14:48:16) and 126 s. (14:48:22). Therefore, it can be judged that the liquefaction Liquefied layer A kind of sloshing occurred at around 14:48:16 to 14:48:22 at K-NET Inage. This means many cycles of shear stress, say around 20 (2) Horizontal buckling on a sloped cycles from 110 s., might have caused the liquefaction at bottom of liquefied layer the K-NET Inage site. And it should be noted that the Fig. 20. Two possible mechanisms of heaving. shaking continued for long time after the occurrence of liquefaction. By referring to the accelerogram at K-NET Urayasu, it is seen that the shaking of the ground at Inage continued for about 3 min after liquefaction was triggered. aftershock. And the houses that had settled during main One more impact to the ground at Inage must have been shock might have settled more during the aftershock. the shaking during the aftershock. Peak horizontal accelerations, composited from NS and 7.2. Timing of the occurrence of liquefaction EW components during the main shock and the aftershock at the 7 K-NET sites, are indicated in Fig. 5.Thepeak Many seismic records were obtained in the Tokyo Bay accelerations during the aftershock were almost half of area, as mentioned before. Among them, the accelero- those during the main shock in the Tokyo Bay area, even grams recorded at K-NET Inage in Chiba, where boiled though, as mentioned above, boiling occurred after the sand was actually observed, are very important because the aftershock at some sites in Urayasu. A similar phenomenon time of liquefaction can be judged from the recorded was witnessed by the inhabitants of Chiba City. Some excess waves. Fig. 19 shows the accelerograph at Inage together pore water pressure, which occurred during the main shock, with that at K-NET Urayasu, which was recorded on the must have brought about complete liquefaction during the ground where liquefaction did not occur. Both records aftershock. In these cases, more cycles of shear stress, for were started at almost the same time, namely, at 14:46:16 example, 100 cycles, might have caused the liquefaction. It is at Inage and 14:46:15 at Urayasu. Urayasu’s wave fre- impossible to evaluate the times of liquefaction at all the quency did not change drastically after the peak sites, but the times must certainly vary depending on the S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 803

SPTN-value footways and alleys without boundaries with the contour Depth (m) 0 1020304050 lines showing the thickness of the F layer under the 2 fine sand groundwater table, it may be said that heaving occurred Filled layer 4 3.45 at the sites where the bottoms of the F layer, in other 4.90 silty fine sand 6 words, the liquefied layer, are sloped. This implies that a 8 kind of horizontal buckling of the surface layer might have 10 fine sand 12 occurred due to the concentration of horizontal compres- 14 14.00 sive stress, as schematically shown in Fig. 20(2). However, 16 silty fine sand more studies are necessary on the mechanism of buckling. 16.45 18 sandy silt 20 20.00 7.4. Plenty of boiled sand and large settlement 22 24 silt 26 A great eruption of sand and a large ground subsidence 28 occurred in the liquefied area. The maximum thickness of 30 29.40 the erupted sand and the maximum ground subsidence 32 sandy silt observed by the authors were about 30 cm and 50 cm, 34 33.40 respectively, as shown in Photos 7 and 8 of the frontispieces, 36 38 respectively. This is the first time the authors have ever seen 40 silt such thick deposited boiled sand in Japan. However, a 42 similar amount of eruption and large subsidence also 44 occurred in Christchurch, New Zealand during the main 46 shock of the earthquake which occurred in September 2010 48 and an aftershock which occurred in February 2011 50 52 (Cubrinovski et al., 2012). The sand in both Christchurch 54 and Tokyo Bay has a lot of fines content. Thus, it is 56 56.10 estimated that in very fine sands, the ejection of water 58 silty fine sand continues for a long time because of the low permeability of 60 59.10 fine sand the liquefied soil. Moreover, fine soil particles are easily 62 uplifted above the ground surface by the ejecting water. And Fig. 22. Soil boring log. the removal of the deposited soil by inhabitants accelerated the settlement of the ground surface even further. sites, because the duration of the shaking due to the 2011 Great East Japan Earthquake was extremely long and was 7.5. Effectiveness of ground improvement followed by a large aftershock after a short time. (1) Proportion of ground improvement methods 7.3. Buckling of roads Many ground improvement works have been implemented in reclaimed lands along Tokyo Bay (Society of The authors saw a strange heaving on a footway of a Construction Industry, 1984), and based on the recon- main street at Takasu in Urayasu City, as shown in Photo 5 naissance work conducted just after the earthquake, no of the frontispieces, on the day after the earthquake. The damage was observed at any of the improved sites. first impression was that the footway heaved due to the Fig. 21 shows the proportion of the various ground uplift force of some buried pipes, such as sewage pipes. improvement methods implemented in lands along After that, however, similar phenomena, namely, heaving, Tokyo Bay (Tokyo and Chiba) by Fudo Tetra Cor- buckling and thrust, were observed on several footways and poration over a period of forty years. The figure in alleys. Some boundaries existed along the footways and indicates that a total of 900 ground improvement alleys, such as the banks of old sea walls and elevated projects have been implemented, and that 70% of them bridges. Therefore, some thrust might have occurred at consist of liquefaction countermeasures, such as the these boundaries due to a kind of sloshing of the liquefied vibratory sand compaction pile (SCP) method, the ground, as schematically shown in Fig. 20(1), because non-vibratory SCP method, the gravel drain (GD) shaking continued for long time after the occurrence of method and the lattice-type deep mixing method. The liquefaction, as mentioned above. compaction methods, including the vibratory and the On the other hand, at Takahama in Ichikawa City, the non-vibratory SCP methods, comprise about 90% of heaving of a footway was observed, although there is no the total liquefaction countermeasure applications. such boundary, as shown in Photo 6 of the frontspieces. (2) Verified cases of improvement The locations of the heaved footways and alleys in (i) Irifune (Urayasu City) Urayasu City, with and without boundaries, are plotted The construction of high-rise and medium- to in Fig. 11. By comparing the locations of the heaved low-rise residential buildings was carried out in the 804 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

Block Story Ground improvement Foundation

SCP□2.0m L=10m Nodular pile L=8m No.1 2F 1F GD∆1.8m L=10m Nodular pile L=8m

No.2 3F SCP□2.0m L=10m Nodular pile L=8m

SCP□2.0m L=10m Nodular pile L=8m No.3 3F GD∆1.8m L=10m Nodular pile L=8m No.4 2F GD∆1.8m L=10m Nodular pile L=8m

No.5 3F SCP□2.0m L=10m Nodular pile L=8m

SCP improved area GD improved area Sandboil

0 50m 100m

Fig. 23. Plane ﬁgure.

+0.0 +0.0 slag(pre) -1.0 sand(pre) -1.0 -2.0 slag(post) -2.0

1458 slag(post) -3.0 -3.0

2065 sand(post) 1750

1460 -4.0 sand(post) -4.0

2000 -5.0 -5.0 2000 -6.0 -6.0 2000

2000 -7.0 -7.0

Elevation (m) -8.0 -8.0 slag(pre) Elevation (m) SCP pile sand(pre) 2000 2000163016301630 1897.5 1897.5 2000 -9.0 -9.0 1897.5 1897.5 2000 Nodular pile slag(post) -10.0 -10.0 slag(post) sand(post) Unit (mm) -11.0 -11.0 sand(post) -12.0 -12.0 0 1020304050 020406080100 SPT N-value Fines content, FC(%)

N 2280 Fig. 25. Distribution of pre- and post-operation SPT -values and ﬁnes content with depth. 2820

boring log, shown in Fig. 22, the upper part of the 2280 site consists of reclaimed and ﬁlled layers, while the lower part of the site has alluvial sand and clay 1800 1800 accumulations. The Irifune district is located in GD pile the A4 area of Fig. 6; it consists of 5 blocks, as Nodular pile illustrated in Fig. 23. The SCP method was adopted Fig. 24. Examples of pile layout. (a) SCP method and (b) GD method. mainly for 3-story buildings in order to increase the bearing capacity and to prevent liquefaction. On Urayasu area in the 1970 s by the Housing Cor- the other hand, the GD method was adopted poration (Yoshii, 1980). The locations of these mainly for 2-story buildings in order to mitigate buildings are indicated in Fig. 6. From the soil liquefaction. The kind of foundation used for each S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 805

Table 2 Gravel Compaction Piles New evaluation standards for the damage to houses.

Grade of damage Evaluation method 1.5m 0.75m Inclination Settlement Non-vibratory GCP (Using gravel) Totally collapsed More than 1/20 Floor to 1 m above ﬂoor Large-scale half-collapsed 1/60 to 1/20 25 cm above footing to ﬂoor Sand Compaction Piles Half-collapsed 1/100 to 1/60 Up to 25 cm above footing 1.5m 1.5m Non-vibratory SCP (Using sand) Table 3 050m Number of damaged houses in Urayasu Chiba by old and new standards (Quoted from the report by the Technical Committee organized by Urayasu City (2012)). Fig. 26. Plane view of the SCP-improved area of the building. Grade of damage Number of houses

Old standard New standard

Totally collapsed 8 18 Zones where Large-scale half-collapsed 0 1541 severe damage Half-collapsed 33 2121 to houses Partially damaged 7930 5096 occurred No damage 1028 1105 Total 8999 9981

the buildings were being constructed (Japan Association for Building Research Promotion, JABRP, 1979). The results of the pre- and post- operation standard penetration tests (SPT), as well as the fines content distributions, are shown in Fig. 25. It can be seen that in the layers where the fines content is low, the SPT N-values (N80) Areas surrounded by lines 1km Black: Liquefied and sewage facilities increased by about 10 or more when iron and steel were damaged Red: Roads were severely damaged slag was used, similar to the case when natural sand Blue: Roads were damaged was used. Yellow: Roads were slightly damaged Following the earthquake, sand boils were observed Fig. 27. Zone where houses were severely damaged in Urayasu City in unimproved areas around the buildings and in (Partially quoted from the report by the Technical Committee organized parks within the residential complex. However, no by Urayasu City (2012)). sand boils were seen within the improved area and no damage occurred to buildings constructed on ground type of building was a spread foundation (contin- that had been improved by either the SCP method or uous foundation) supported by 8 m-long nodular the GD method. piles driven at the points where the side walls (ii) Tatsumi (Koto Ward in Tokyo) intersect. These piles were used to ensure sufficient A medical center building is located in the bearing capacity by shaft friction in the non- reclaimed land along Tokyo Bay shown in Fig. 7. uniform upper sand layer inter-bedded with lenses The foundation ground at the site consisted of a of silt. The improvement specifications of the SCP soft and loose reclaimed layer in the upper 13 m method consisted of sand piles, 800 mm in dia- with SPT N-values (N80) ranging from 1 to 7 and meter, 10 m in length, with square grids having a with fines contents from 20 to 40%. This was spacing of 2.0 m (improvement ratio as ¼12.5%). underlain by soft silty clay. The water level was The improved area extended 5 m around the very shallow, about 0.7 m from the ground level. building. On the other hand, the improvement The building is 5 stories high and supported by specifications of the GD method were gravel piles, piles. Following the liquefaction assessment, the site 400 mm in diameter, with a spacing of 2.6 m 1.3 was judged to have the high liquefaction potential of m on the rectangular grid. Examples of the pile G.L.0.7 m to G.L.13 m. Consequently, the non- layout for each method are shown in Fig. 24. vibratory SCP method was adopted at this site as a Trial tests for the SCP method, using converter countermeasure against liquefaction. The perfor- slag as the filling material, were carried out while mance requirements for ground improvement at 806 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

Max. inclination of Totally 60 totally collapsed collapsed is assumed 70/1,000. Min. of partially damaged is assumed 3/1,000. 40 Large-scale half collapsed

20 Half

Inclination of houses ( /1,000) collapsed Partially 㧔1㧕Two houses (2) Four houses are No damage Damaged 0 are close close 0 2000 4000 6000 Number of houses (1) Urayasu City Direction of tilting

350 375 325 350 Partially damaged 300 325 Fig. 30. Effect of adjacent houses on the inclination of houses. 275 300 Half collapsed 250 275 Totally collapsed 225 250 200 225 factor against liquefaction, FL, at all points should be 175 200 greater than 1.0 for a maximum surface acceleration 150 175 125 150 of amax¼350 gal and maximum cyclic lateral defor- 100 125 mation, D (Architectural Institute of Japan, 2001), 75 100 cy 50 75 of less than 5 cm. 25 50 The improvement speciﬁcations were a square-grid

Inclination of houses ( /1,000) 025 0 5 10 15 20 spacing of 1.5 m (as¼16.7%) and a sand pile length Number of houses of 12 m. In the area surrounding the improved site, (2) Abehikona in Yonago City gravel was used instead of sand to dissipate the excess water pressure from the liqueﬁed area, as shown in Fig. 28. Frequency distributions of the number of damaged houses. Fig. 26. The effectiveness of this method was veriﬁed by a building on Rokko Island during the 1995 Hyogo-ken Nambu Earthquake (Architectural Institute of Japan, AIJ, 2006). As shown in Photo 9 of the frontispieces, although liquefaction-induced damage was observed outside the improved area, no damage was observed within the improved area.

8. Remarkable damage to structures due to liquefaction

8.1. Settlement and tilt of houses

According to the results compiled by the Ministry of Liquefied Land, Infrastructure, Transport and Tourism, about Liquefied 27,000 houses were damaged due to liquefaction. About half of the damaged houses are located in the Tokyo Bay area. In Urayasu City, the severely damaged houses were located in the zones shown in Fig. 27. Photo 10(1) and (2) (1) During main shock (2) During aftershock of the frontispieces show a damaged house taken from the outside and the inside, respectively. Although no damage Fig. 29. Possible effect of an aftershock on the settlement of a house. was observed for the walls or the windows, the house settled and tilted about 40/1000. Strip footing foundations or mat foundations are used to build houses in Japan. The this site were as follows: (1) safety factor against house shown in Photo 10 has a strip footing foundation. In liquefaction, FL, at each point should have an SPT general, strip footing foundations tend to deform and N-value greater than 1.0 for a maximum surface cause structural damage to superstructures if differential acceleration of amax ¼200 gal and (2) average safety settlement occurs. However, as shown in Photo 10, this S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 807

Table 4 Brief summary of the damage to other structures in Urayasu City (Partially quoted from the report by the Technical Committee organized by Urayasu City (2012)).

Facility Damage to structures

Road [Damage rate] National road: 0%, Prefectural road: 27%, City road (main road): 43%, City road (local road): 34% Bridge Settlement of approach bank: 4 bridges River or sea wall Settle and tilt of river wall: 4 sites. Settle and tilt of sea wall: 4 sites. Park Damaged park: 35 parks Sewage [Damage rate of pipe] Motomachi: 0%, Nakamachi: 81%, Shinmachi: 19%. [Damage rate of manhole] Motomachi: 0%, (waste water) Nakamachi: 69%, Shinmachi: 31% Water Leaked site: 605 sites Gas Tilt of shed of governor station: 2 stations. Damage to middle pressures pipe: 1 joint. Damage to low pressure pipe: 18 joints. Electric power Settle and tilt of electric poles. Damage to buried cables. Telegraph Settle and tilt of electric poles. Damage to buried cables.

Large settlement, which means the penetration of houses Kairaku Horie Nekozane into the ground, such as a penetration of 30 cm, caused damage to water, sewage water and gas pipes by tearing or Mihama bending. Moreover, in the heavily tilted houses, inhabi- Higashino Irifune Fujimi tants felt giddy, sick and nauseous, and it was difﬁcult for Tomioka them to live in their houses after the earthquake. For Hinode Imagawa example, as about 100 houses settled and tilted due to Benten Akemi liquefaction at Abehikona housing lot in Yonago City Maihama during the 2000 Tottoriken-seibu Earthquake, houses that Takasu Tekkodori had tilted heavily, more than about 10/1000 had to be Tokyo Disneyland restored to a horizontal condition (Yasuda and Ariyama, Minato 2008). However, before the 2011 Great East Japan Earth- Damaged pipe quake, houses that had settled and tilted due to liquefac- Uplift of manhole Chidori Settle of manhole tion used to be judged as having partially collapsed or been Shear of manhole damaged, because there had been no damage to the walls 1km Damage to lid of or windows, although it has been desired that both manhole settlement and inclination would be considered as a certain Fig. 31. Damaged sites for sewage pipes and manholes in Urayasu City degree of damage to houses. (Quoted from the report by the Technical Committee organized by Then, in May, the Japanese Cabinet announced new Urayasu City (2012)). evaluation standards for the damage to houses by these two factors, settlement and inclination, as shown in Table 2. A new classiﬁcation, ‘‘large-scale half-collapsed Sloshing of liquefied house’’ was also introduced, and houses tilting more than ground 1/20, 1/20 to 1/60 and 1/60 to 1/100 are judged as totally collapsed houses, large-scale half-collapsed houses and half-collapsed houses, respectively, in the new standards. Meander and pull out The number of damaged houses in Urayasu City, accord- Plane of joint of pipe ing to the new standards, is listed in Table 3 together with the number counted by the old judging method (Urayasu City, 2011). The numbers of totally and half-collapsed Major road houses increased drastically, and the number of houses damaged more severely than half-collapsed grew to 3680. Subgrade Sloshing The frequency distribution of the number of damaged houses is counted from Table 3 and plotted in Fig. 28 Shear of manhole together with the damage in the Abehikona housing lot Cross section due to the 2000 Tottoriken-seibu Earthquake. The maximum inclinations in Urayasu City and Abehikona are about 60/1000 and 37/1000, respectively. Moreover, Fig. 32. Unique damage to sewage manholes and pipes. although the average inclination in Abehikona was 10/ 1000 to 15/1000, many houses tilted more than 15/1000 in house suffered no obvious structural damage despite the Urayasu City. Therefore, it can be said that the houses in liquefaction settlement of its strip footing foundation. Urayasu tilted more severely than the houses in 808 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

Abehikona. The settlement of the damaged houses is not The damage to roads depended on the thickness of the clear because it is not easy to measure settlement. How- subgrade. The thickness of the subgrade of major roads, ever, it is inferred that larger settlement occurred in minor roads and sidewalks is more than 1 m with 3–4 layers Urayasu City than in Abehikona. As mentioned above, of asphalt pavement, about 0.5 m with 2 layers of asphalt the occurrence of liquefaction must have been affected by pavement and about 20 cm with 1 layer of asphalt pave- the aftershock. Not only the occurrence of liquefaction, ment, respectively. The major roads escaped severe damage, but also the settlement and the inclination must have been whereas minor roads and sidewalks suffered severe damage affected by the aftershock. The groundwater table such as settlement, waving, heaving and cracks. increased after the main shock and boiled muddy water Bridges for roads and railways supported by piles had covered the ground surface until the aftershock at many no damage without the settlement of the approach bank on sites. Then, the settlement of houses was excitable during several bridges. Buildings supported by piles also escaped the aftershock, although the shaking amplitude was less damage. However, the inhabitants of apartment houses than that during the main shock, as is schematically shown supported by piles were forced to live inconvenient lives for in Fig. 29. several days because of the shutdown of lifelines and the The tilting of houses is derived from the non-uniform ground settlement at the entrances of their apartment settlement. According to the authors’ previous study on houses. the non-uniform settlement of houses, several factors affect River walls and sea walls settled and tilted at eight sites, non-uniform settlement. Among them, the effect of adja- but houses were not affected by the damage to the walls in cent houses was dominant in the Abehikona housing lot Urayasu City. On the contrary, the sheet pile type of river (Yasuda and Ariyama, 2008). A similar tendency was walls tilted towards rivers and caused damage to adjacent observed in the Tokyo Bay area, as is schematically shown houses and a warehouse at two sites in Funabashi City, as in Fig. 30. If two houses are closely constructed, these shown in Photo 11 of the frontispieces. The river wall in houses will tilt inward; if four houses are closely con- this photo moved about 2 m towards the river, and the structed, these houses will tilt toward the center. ground behind the wall flowed towards the river up the One more interesting thing to note is the effect of the ground 25 m from the wall, resulting in the tearing of houses. depth of the groundwater table on the damage to houses. However, no other river or sea walls were moved seriously, The average depth of the water table for the totally although a lot of walls exist in the Tokyo Bay area. collapsed, the large-scale half-collapsed, the half- Lifeline facilities for water, sewage, gas, electric power collapsed and the partially damaged houses in Urayasu and telegraph were severely damaged due to liquefaction. City were G.L.1.38 m, G.L.1.78 m, G.L.1.84 m and Buried pipes were bent or pulled out and electric poles G.L.2.10 m, respectively. seriously settled and tilted. However, details on the By the way, many inhabitants along Tokyo Bay are damage to buried pipes are still not available because facing the serious problem of how to restore their damaged excavations and permanent restorations have not yet been houses. The problem is further complicated by the pro- conducted. Only a bit of information on the damage has spect of re-liquefaction during future earthquakes or been clarified based on inspections by pipe cameras. In aftershocks. And, not only the restoration, but also some sewage facilities, pipes meandered or were broken, joints countermeasures against re-liquefaction must be applied, were pulled out and pipes were filled with muddy water. but problems regarding the cost and the technique for Many manholes were sheared in a horizontal direction and treating grounds under existing structures are encountered. filled with muddy water; however, few manholes uplifted. Thus, the early development of effective and economic The damaged sites of sewage pipes and manholes in measures against liquefaction for existing timber houses Urayasu City, shown in Fig. 31, are almost all in the are being created by several organizations. Moreover, the zones where the severely damaged houses are. Although applicability of special measures to improve an area by the mechanism of these unique types of damage is still decreasing the groundwater table is being studied. under study, one author’s idea is illustrated in Fig. 32.As mentioned before, a kind of sloshing around of the 8.2. Damage to other structures liquefied ground might have occurred, due to the long duration of shaking, and caused a thrust of the roads. By Other structures, lifelines and roads were severely the same movement of the ground, pipes might have damaged in the liquefied zones from Shinkiba to Chiba meandered violently in a horizontal direction, resulting in City. Table 4 presents a brief summary of the damage to the pulling out or the breaking of joints, and eventually the other structures in Urayasu City (Urayasu City, 2011). liquefied muddy water invading the pipes. Manholes might Notes are necessary for the amounts of damage to under- have been sheared due to the horizontal force, causing the ground pipes and manholes because the numbers were pressurized and liquefied muddy water to come into the counted during temporary restoration works. The actual manholes, eventually spewing out from the holes in the lids damage will be defined during the permanent restoration of the manholes, as impressively shown in Photo 4(8). work which will be done soon. Fortunately, or unfortunately, the muddy water invading S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810 809 into the sewage pipes and manholes might have prevented Acknowledgments such uplift. Some of the results cited in this paper are quoted from a 9. Conclusions report by the Technical Committee on Measures against Liquefaction, chaired by Prof. K. Ishihara and organized The 2011 Great East Japan Earthquake caused severe by the Urayasu City Government. Several graduate stu- liquefaction in the Tokyo Bay area. Immediately after the dents at Tokyo Denki University helped with the site earthquake, the authors investigated the liquefied sites for investigation. Mr. K. Ogawa provided us with important about 10 days. They conducted and/or reviewed several photos. Many useful comments were given to us by JGS studies on the soil conditions of the liquefied sites, the members and others. The authors would like to express damage to structures and the methods to restore them. The their sincere appreciation to all of them. following conclusions were derived from these studies:

(1) Severe liquefaction occurred in reclaimed lands from Shinkiba in Tokyo through Urayasu, Ichikawa and References Narashino Cities to Chiba City. These lands were constructed after around 1966 with soil dredged from Architectural Institute of Japan, 2001. Recommendations for Design of the bottom of the bay. Building Foundations, pp. 66–67 (in Japanese). Architectural Institute of Japan (AIJ), 2006. Recommendations for (2) The dredged and filled soils were estimated to have Design of Ground Improvement for Building Foundations, pp. 363– been liquefied by the earthquake, but their strength 364 (in Japanese). against liquefaction was not so low because they Boulanger, R., 2012. Liquefaction in the 2011 Great East Japan Earth- contained a high fines content. quake: Lessons for U.S. Practice. Proceedings of the International (3) Seismic intensities in the liquefied zones were not high, Symposium on Engineering Lessons Learned from the 2011 Great 2 East Japan Earthquake, 655–664. 160–300 cm/s in peak surface acceleration, although the Chiba Prefecture: Chiba Prefecture Soil Quality Environment Informa- liquefied grounds were covered with boiled sand. The tion Bank, /http://www.pref.chiba.lg.jp/suiho/chishitsu.htmlS. very long duration of the main shock, and an aftershock Cubrinovski, M., Henderson, D., Bradley, B., 2012. Liquefaction impacts 29 min later, should have induced severe liquefaction. in residential areas in the 2010–2011 Christchurch Earthquakes. (4) Two remarkable characteristics of the liquefied Proceedings of the International Symposium on Engineering Lessons Learned from the 2011 Great East Japan Earthquake, 811–824. grounds were observed: (i) the buckling of sidewalks Endoh, T., 2004. Historical review of reclamation works in the Tokyo Bay and alleys and (ii) much boiled sand and large ground area. Journal of Geography 113 (6), 785–801 (in Japanese). subsidence. The former might have been induced by a Geospatial Information Authority of Japan, /http://www.gsi.go.jp/cais/ kind of sloshing around of the liquefied ground. The topic110422-index.htmlS. latter must have occurred because the liquefied soil was Ishihara, K., 2012. Liquefaction in Tokyo Bay and Kanto Region in the 2011 Great East Japan Earthquake. Proceedings of the International very fine. Symposium on Engineering Lessons Learned from the 2011 Great (5) Many reclaimed grounds have been improved by the East Japan Earthquake, 63–81. sand compaction pile (SCP) method, the gravel drain Japan Association for Building Research Promotion (JABRP), 1979. (GD) method and other methods. These improved Study on Application of Sand Compaction Pile Method Using grounds escaped damage due to liquefaction. Converter Slag (in Japanese). Japan Road Association, 2002. Specification for Highway Bridges (in (6) About 27,000 houses were damaged in the Tohoku and Japanese). Kanto districts of Japan due to liquefaction caused by JGS, 2010. Geotechnical Conditions in the Kanto Region, Kanto Branch the earthquake. About half of the damaged houses are of the Japanese Geotechnical Society, 132 p., (in Japanese). located in the Tokyo Bay area. In Urayasu City, where National Research Institute for Earth Science and Disaster Prevention / houses were seriously damaged, 3680 houses were more (NIED). K-NET WWW service’’, Japan 2011. http://www.k-net. bosai.go.jp/S. than partially destroyed. Houses settled substantially Ogawa, K., 2011. Private communication. and tilted seriously. Society of Construction Industry, 1984. Handbook of Soft Ground for (7) Lifelines and roads were severely damaged in the Civil and Architectural Engineer. Applications (in Japanese). liquefied zones. The major roads were not severely Tokimatsu, K., Katsumata, K., 2012. Liquefaction-induced Damage to damaged, but minor roads and sidewalks suffered Buildings in Urayasu City during the 2011 Tohoku Pacific Earthquake. severe damage, such as settlement, waving, heaving Proceedings of the International Symposium on Engineering Lessons Learned from the 2011 Great East Japan Earthquake, pp. 665–674. and cracks. Sewage pipes meandered or were broken, Urayasu City, 2012. Data Compiled by the Technical Committee on joints were extruded from the ground, and pipes were Measures against Liquefaction /http://www.city.urayasu.chiba.jp/ filled with muddy water. Many manholes were sheared menu11324.htmlS, 141p (in Japanese). horizontally and filled with muddy water; however, few Wakamatsu, K., 2011. Private communication. manholes were uplifted. This remarkable damage to Yasuda, S., Ariyama, Y., 2008. Study on the Mechanism of the liquefaction-induced Differential Settlement of Timber Houses occurred buried pipes and manholes might also have occurred during the 2000 Totoriken-seibu Earthquake. Proceedings of 14th due to a kind of sloshing around of the liquefied World Conference on Earthquake Engineering, Beijing, Paper No. ground. S26-021. 810 S. Yasuda et al. / Soils and Foundations 52 (2012) 793–810

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