Liquefaction in Tohoku district during the 2011 off the Pacific Coast of Tohoku Earthquake

Information on the liquefaction and the liquefaction-induced damage in the Tohoku district during the 2011 off the Pacific Coast of Tohoku Earthquake has been compiled. The liquefaction in this report was mainly identified by sand boils. It caused damage to earth structures and residential houses, as well as the uplift of manholes. A comparison of geological maps and aerial photos, before and after the earthquake, shows that many of the liquefied sites were old river beds and developed areas. Liquefaction in the tsunami-affected areas was difficult to identify as the evidence of liquefaction had been washed away by the tsunami. However, the liquefaction was identified through interviews with residents and by photos and videos taken before the arrival of the tsunami. Liquefaction was also observed at Sendai Airport, but the runaway was not damaged because it had been remediated against soil liquefaction.     

Building damage during the 2011 off the Pacific coast of Tohoku Earthquake

This paper describes the building damage incurred during the 2011 off the Pacific coast of Tohoku Earthquake in relation to ground motion characteristics. First, with regard to the long-duration ground motion, the damage of a base-isolation building is described. The damage to the 8–9-story buildings in the Aobayama campus of Tohoku University, in a hilly zone, is also described in relation to site-specific ground motion amplification. As specific building damage, pile foundation damage is described. The ceiling board drop damage is also presented as an example of non-structural element damage. Finally, the lessons learnt from the earthquake in terms of building damage are summarized.     

Geo-environmental issues induced by the 2011 off the Pacific Coast of Tohoku Earthquake and tsunami

The 2011 off the Pacific Coast of Tohoku Earthquake of March 11, 2011, caused devastating geotechnical and geo-environmental issues mainly in the coastal area of the Tohoku and North-Kanto Regions, Japan. As a result of the earthquake and subsequent tsunami, approximately 23,000 Gg (23,000,000 t) of disaster debris was generated, with more than 12 million m³ of tsunami deposits left in the flooded area. The geotechnical utilization of the soil fraction in the disaster debris and tsunami deposits has presented a huge challenge to geotechnical engineers since (1) the clearance of debris and tsunami deposits is an urgent task which must be completed within a few years and (2) although a large amount of waste-mixed soil can be used in the construction of new embankments and levees to protect the coast from future tsunamis, their geotechnical properties have temporal and spatial variations. This paper summarizes the current status on the generation, clearance, and treatment and utilization of disaster debris and tsunami deposits from geotechnical and geo-environmental viewpoints. In addition, the environmental monitoring data on soil and groundwater quality conducted over the affected area is briefly reviewed. The results of several wide-area monitoring efforts conducted by different organizations indicate that no significant soil or groundwater contamination has occurred. However, the localized contamination near industrial plants where toxic chemicals leaked due to the earthquake and tsunami needs to be carefully taken into consideration during future revival and redevelopment works. Another serious geo-environmental issue is the management of the radioactive contamination of surface soils caused by the accident at the Fukushima First Nuclear Power Plant. This paper summarizes the distributions and expected behaviours of radioactive Caesium in soils and groundwater, and outlines the possible remediation options for dealing with this contamination.     

The damage to hillside embankments in Sendai city during The 2011 off the Pacific Coast of Tohoku Earthquake

The 2011 off the Pacific Coast of Tohoku Earthquake resulted in severe damage to housing and housing lots. In particular, the hillside embankments for residential use surrounding the downtown of Sendai city suffered serious damage. Many hillside lands which had been damaged during the 1978 off Miyagi-Prefecture earthquake were subjected to further damage. Typical damaged hillside embankments in Sendai city were investigated and the causes of the damage were discussed in this paper. The main cause of the damage to housing was not the seismic motion but the ground displacement of the fill embankment. A comparison of the damage from the 2011 earthquake with that from the 1978 earthquake indicates that the countermeasures constructed after the 1978 earthquake performed well in that they prevented large landslide type failure; however, they were not successful in reducing the amount of damage to housing or housing lots due to ground displacements from cracks, differential settlement, and shallow slips. A classification of failure types of fill embankment is proposed to be of assistance in the choice of countermeasures.     

Damage statistics (Summary of the 2011 off the Pacific Coast of Tohoku Earthquake damage)

The 2011 off the Pacific Coast of Tohoku Earthquake, which occurred on March 11, 2011, caused enormous damage, particularly to the strip of land along the Pacific Ocean from the Tohoku Region to the Kanto Region, due to seismic motion and the tsunami it triggered. This report presents an outline of the earthquake and summarizes the associated seismic damage to social infrastructure facilities.     

Soil liquefaction observed at the lower stream of Tonegawa river during the 2011 off the Pacific Coast of Tohoku Earthquake

Earthquake reconnaissance investigations were carried out at regions located along the lower stream of Tonegawa River where widely spread soil liquefaction and associated phenomena were observed following the main shock and aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake. A multiple series of Swedish Weight Sounding tests were carried out at Sawara of Katori City, Hinode of Itako City, and Wanigawa and Fukashiba of Kamisu City. The soil profiles responsible for the damage inflicted by soil liquefaction were demonstrated along with the help of SPT data. At some locations where the soil samples of erupted sand boils were retrieved, the profiles of relative density and factor of safety against liquefaction with depth are estimated and discussed in detail. The use of Swedish weight sounding tests along with a help of SPT soil profiling proved an effective method for detecting liquefiable soil layers responsible for widespread soil liquefaction induced damage.     

Damage to railway earth structures and foundations caused by the 2011 off the Pacific Coast of Tohoku Earthquake

Statistics are compiled on the damage to railway earth structures, soil retaining walls and bridge foundations caused by the 2011 off the Pacific Coast of Tohoku Earthquake in Japan and the subsequent tsunami. Several case histories are reported on the damage they created and the rehabilitation works implemented, including the collapse of a high cut slope, the excessive settlement of embankments in lowland areas, the significant scoring of the backfill soil of bridge abutments, the restoration works of tilted bridge foundations and the tsunami-induced collapse of soil-retaining walls and bridge foundations. The good performance of well-designed foundations, which were able to survive the impact of the earthquake, particularly the effects of the earthquake-induced liquefaction of the subsoil layers, is also described.     

Safety inspections and seismic behavior of embankment dams during the 2011 off the Pacific Coast of Tohoku earthquake

Immediately after the 2011 off the Pacific coast of Tohoku Earthquake, special safety inspections were carried out at over 300 dams in the affected area. Damage was identified at more than 10% of the inspected dams, with embankment dams showing a slightly higher ratio. Damage to embankment dams included relatively wide and/or long cracks mainly on the crest of earthfill dams, cracks in the impervious membrane of asphalt faced rockfill dams (AFRDs) and temporary increase in leakage. However, none of the dams under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) sustained damage severe enough to threaten the safety of the dam, although an old earthfill embankment dam for an irrigation pond located outside the area regulated by the River Law was breached due to the earthquake. In this paper, the results of special safety inspections are summarized, as well as those of subsequent detailed investigations of several embankment dams under the jurisdiction of MILT. The features of the earthquake motions observed at the dam foundations during the earthquake and their effects on the behavior of embankment dams are also discussed.     

2011年日本东北地区太平洋近海地震地基液化灾害综述

2011年3月11日,日本太平洋东海岸发生M_w 9.0级大地震,并引发巨大海啸,导致了日本东北和关东地区大面积的地基液化震害。通过现场震害调查和最新资料分析,首先较为系统地介绍了日本地震受灾区的液化宏观现象和典型震害特征。其次,研究了余震再液化和地震-海啸耦合灾害的破坏机制和特征,指出余震再液化受地震力大小、应力历史及超孔隙水压力消散程度的影响,并将地震和海啸耦合破坏过程分为3个阶段：震后液化阶段、间歇期恢复阶段、海啸流滑破坏阶段;最后,对此次强震中有关抗液化地基处理方法的有效性进行了分析与探讨,以期为今后的地基抗液化设计提供参考与借鉴。     

Lessons for countermeasures using earth structures against tsunami obtained in the 2011 Off the Pacific Coast of Tohoku Earthquake

Since many infrastructures, such as sea walls, sand beaches, forests, etc., were severely damaged or destroyed by the tsunami that occurred due to the 2011 Off the Pacific Coast of Tohoku Earthquake, it is said that the resistant functions of the above structures against tsunami attacks did not perform well. However, some structures are known to have resisted the tsunami, based on field surveys conducted after the earthquake by the authors and others; and thus, the resistant functions of those infrastructures against tsunami should be estimated more properly. This paper focuses on earth structures, including river levees and road embankments, both damaged and undamaged, at 13 sites in Miyagi Prefecture, Chiba Prefecture, and Ibaraki Prefecture. They have been investigated through field surveys and other related data, such as satellite photographs taken before and/or after the tsunami. Furthermore, 10 dug pools, eroded by the flood stream on the back side of sea walls and banks during the tsunami, are also investigated to clarify their effects against tsunami attacks for use as future hardware countermeasures. Based on the above field investigations, several important lessons on hardware countermeasures against tsunami, using earth structures, are discussed. And, performance-based design concepts for reconstruction after this earthquake and for the reduction of future tsunami damage are discussed and proposed.     

Building damage associated with geotechnical problems in the 2011 Tohoku Pacific Earthquake

An overview of the geotechnical aspects of the building damage due to the 2011 Tohoku Pacific Earthquake is presented, based on field reconnaissance made after the earthquake. It is shown that (1) Extensive soil liquefaction occurred along the coast of Tokyo Bay and around the floodplain of the Tonegawa River. Liquefaction was primarily found within the relatively newly reclaimed area, with numerous sand boils and large ground settlements up to 60 cm, accompanied by the settlement/tilting of wooden and reinforced concrete buildings supported by spread foundations. The extent and the distribution of the damage were significantly affected by the local soil conditions, including the thickness and the age of the reclaimed fills, the depth to the bedrock or the natural site period, and whether remedial measures had been taken against soil liquefaction, as well as the effects of structure–soil–structure interaction. (2) Numerous houses in Sendai's hilly residential areas constructed with the cut-and fill method were badly damaged not only by the simple collapse of retaining walls, but also by slope failures in the fills. It was found that most of the slope failures occurred on earth fills. (3) Several pile-supported buildings tilted and settled not only in the Tohoku region, but also on the Kanto plain, implying damage to pile foundations. Ground subsidence with sand boils around those buildings suggests that soil liquefaction might have played a significant role in intensifying the damage. (4) Within Onagawa and Rikuzen-Takata, several steel and reinforced concrete structures were knocked over by tsunami surges, probably after having suffered damage to their pile foundations. Much of the pile damage was concentrated (a) at the joints between pile caps and the piles themselves and (b) near the pile heads. The buildings suffering such damage were old; apparently their pile foundations were not designed to withstand earthquakes.     

Damage patterns of river embankments due to the 2011 off the Pacific Coast of Tohoku Earthquake and a numerical modeling of the deformation of river embankments with a clayey subsoil layer

Due to the 2011 off the Pacific Coast of Tohoku Earthquake, which had a magnitude of 9.0, many soil-made infrastructures, such as river dikes, road embankments, railway foundations and coastal dikes, were damaged. The river dikes and their related structures were damaged at 2115 sites throughout the Tohoku and Kanto areas, including Iwate, Miyagi, Fukushima, Ibaraki and Saitama Prefectures, as well as the Tokyo Metropolitan District. In the first part of the present paper, the main patterns of the damaged river embankments are presented and reviewed based on the in situ research by the authors, MLIT (Ministry of Land, Infrastructure, Transport and Tourism) and JICE (Japan Institute of Construction Engineering). The main causes of the damage were (1) liquefaction of the foundation ground, (2) liquefaction of the soil in the river embankments due to the water-saturated region above the ground level, and (3) the long duration of the earthquake, the enormity of fault zone and the magnitude of the quake. In the second part of the paper, we analyze model river embankments on a foundation ground with various soil profiles, including a clayey soil layer and various ground water tables, using a dynamic liquefaction analysis method. From the analysis results, we find the effects of the soil profiles and the duration time of the earthquake motion on the deformation behavior of the river embankments. The results are consistent with those of the investigation of the features of the deformation and the failure of the embankments due to the 2011 off the Pacific Coast of Tohoku Earthquake.     

Liquefaction in the Kanto region during the 2011 off the pacific coast of Tohoku earthquake

The present text is a summary of liquefaction events that occurred in the Kanto Region during the 2011 off the Pacific coast of Tohoku Earthquake, excluding those events in the Tokyo Bay area that are discussed elsewhere. Most liquefaction occurred in the abandoned river channels and former lakes that had been recently filled with liquefiable soils. Noteworthy was the damage to private housing lands and river dikes that had not been well treated against liquefaction risk. Many sites experienced repeated liquefaction after former earthquakes in 1923 or 1987, if they existed in those times. In contrast to the recent liquefaction-prone soils, more-aged sands scarcely liquefied because of what is called the “ageing” effect. The present study analyzed cases in Tokyo area to quantitatively assess the temporal development of ageing so that liquefaction risk in more aged soils might be reasonably assessed. In the appendix, remarks are made of the reliability of air-photo survey in quick detection of liquefaction sites.     

Reconnaissance report on damage in and around river levees caused by the 2011 off the Pacific coast of Tohoku earthquake

The gigantic earthquake on March 11, 2011, caused significant damage in and around river levees over a vast area. Because the amount of damage was on such a huge scale, emergency restoration was difficult and many lessons were learnt. The cause of the damage in most cases was liquefaction either in the foundation or in the levee body, and the latter was recognized as a new technical problem. Many levees in the coastal area experienced the combined effects of the tsunami with the co-seismic subsidence of the earth's crust. Among the many examples of damage, one positive issue was that damage mitigation measures such as drainage and soil improvement were found to be effective. The present text addresses the findings and lessons learnt from the authors' emergency activities after the quake.     

日本“3.11”地震波MYG004与常用地震波特性的对比分析

日本“3.11”大地震记录波中的MYG004波是迄今为止记录到的地面峰值加速度最大的地震波.文章在调整MYG004波加速度峰值后,从加速度反应谱、比能密度、输入能能量谱三个角度将其与一组常用地震动加速度时程作对比,分析其频谱特性;并通过一个8层某框架结构的弹塑性时程分析,进行验证.     

The impact of the 2011 Tohoku earthquake tsunami disaster and implications to the reconstruction

The authors conducted a comprehensive study to identify the impact of the 2011 Tohoku tsunami disaster and to understand the lessons towards the reconstruction of Tohoku to build tsunami-resilient community. First, the authors identified the extent of tsunami inundation zone by field measurement and satellite remote sensing. A specific index for optical satellite images was applied for the extraction of tsunami inland penetration calibrated with the ground truth data (field survey data). Second, an integrated investigation of field measurement and aerial photo and video inspections with spatial information sciences was performed to understand the hydrodynamic aspect of tsunami inland penetration with a form of tsunami flow velocity and hydrodynamic force, and the preliminary results lead to new understandings of structural vulnerability against the 2011 tsunami with a form of tsunami fragility curve and an implication for land use management and relocation planning to reconstruct resilient coastal communities.     

硬土场地地震动概率反应谱分析

结构抗震设计一直以统计平均值为设防水准,此方法简单但缺乏概率意义的评估值。本文基于硬土场地内309条新获得的地震动记录,建立周期、区间与概率值三者的三维概率分布图,发现概率值难以集中在区间值为1附近,说明以统计平均值为设防水准得出的地震作用概率水平并不相同,应采用统一的累积概率水准进行抗震设防。为此建立了三维累积概率分布图,得出了不同概率保证下的地震影响系数反应谱,并拟合出8度设防水准下不同概率保证的地震影响系数反应谱回归公式。