The 2011 Off the Pacific Coast of Tohoku Earthquake which occurred on March 11, caused serious damage to the infrastructural facilities in Tohoku and Kanto districts due to the strong motion of the earthquake and the subsequent tsunami. This paper includes a brief outline of the earthquake, the earthquake damage to various facilities, and the main geotechnical engineering problems which have emerged after this disaster.

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The Tsunami triggered by the 2011 off the pacific coast of Tohoku Earthquake resulted in huge damage to infrastructures in Tohoku and Kanto area of eastern Japan. This paper is a summary of the investigation related to the geotechnical disaster brought by the earthquake and the associated tsunami in the Aomori prefecture and northern areas of the Iwate prefecture. In the investigated area, rather than the earthquake itself, the disaster was compound (e.g. tsunami related geo-disaster and/or liquefaction related hazard, etc). The paper specially focuses on the disaster brought to the waterfront structures along the coastal area considering the effect of the earthquake and its intensity, the leading wave as well as the backrush of the tsunami, and the structural form, etc.

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Widespread geotechnical damages were caused in eastern Japan by the earthquake motion and tsunami in 2011 off the Pacific Coast of Tohoku Earthquake. Large tsunami attacked the coastal area of eastern Japan and caused damages to buildings, breakwaters, tide embankments and river levees. The joint reconnaissance team of Tohoku and Shikoku branches of Japanese Geotechnical Society investigated the geotechnical damages in south-central coastal area of Iwate Prefecture at the beginning of April and June. This report summarizes the geotechnical hazards and the damages of port structures, roads, railways, river levees and buildings caused by the earthquake motion and tsunami in 2011 off the Pacific Coast of Tohoku Earthquake in south-central coastal area of Iwate Prefecture.

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This paper reports geotechnical damages in the northern area of Miyagi prefecture caused by the 2011 off the Pacific coast of Tohoku Earthquake on March 11, 2011. A joint reconnaissance team organized by Tohoku branch and Kansai branch of the Japanese Geotechnical Society carried out extensive field surveys in the area from April 5 to 10 and from April 29 to 30, 2011. This paper consists of the main results from these surveys and subsequent researches on the damage such as failure of river embankments and coastal levees, coastal erosion caused by tsunami, damage of port and harbor facilities, failure of cut and banked slopes of roads and railroads, and occurrence of liquefaction and subsidence. Although some results have already been reported as news flash to the Journal of the Japanese Geotechnical Society, this paper provides inclusive summaries and more detailed investigations on the damage in the northern area of Miyagi prefecture. In separate sections of this paper, outlines of the damage in each object are briefly summarized, and then several typical damage cases are presented and these mechanisms are discussed in detail.

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Damage to ground and earth structures in the central Miyagi Prefecture area during the 2011 off the Pacific Coast of Tohoku earthquake is presented mainly focusing on the soil liquefaction. Damage to the Naruse River and the Yoshida River are much significant compared with the past earthquakes such as the 1978 Miyagiken-oki earthquake. Sand boils were observed at the paddy or dry filed outside the river dike, flood channel and toe of the slope of the river dike. Fill or reclaimed material of the old river channel is supposed to liquefy in the former two cases whereas dike material is supposed to liquefy in the latter case. Damage in the inland area is mainly occurred at the fill or newly developed area; damage occurred locally and not significant in general. Damage in the coastal area is washed out by the tsunami, but significant liquefaction is confirmed at some places from the observation before the tsunami.

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The seismic damages to geo-structures in the southern district of Miyagi prefecture during the 2011 off the Pacific coast of Tohoku Earthquake were discussed in this paper. The damages to hillside embankments and river embankments were discussed in some detail, in which the role of high degree of saturation of soils was emphasized. The subsidence of ground due to both the tectonic movement occurred during the earthquake and the consolidation of clayey soils weakened by seismic loadings was briefly discussed. The hazard to the foundations of buildings owing to the tsunami propagation was also discussed with paying attention to scour and liquefaction.

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The Tohoku district of Japan suffered serious damage by the 2011 off the Pacific coast of Tohoku earthquake. This report describes the results of investigation carried out by the joint investigation team composed of the members in Tohoku and Kanto Branches of the Japanese Geotechnical Society. Their effort was concentrated into the investigation of damage in the residential lands in Sendai City intensively. In this report, the damage mechanism of each residential land is discussed, based on the preliminary geotechnical information such as the land development histories. In one case of residential land, several measures such as landslide prevention piles were made just after a past earthquake in 1978, and their effectiveness could be evaluated by the damage extents of houses induced by the 2011 earthquake. It is demonstrated that employing measures to restrain the deformation of the ground surface even after strong earthquakes will be advantageous for decreasing the risk for earthquake-induced damage to houses.

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This report describes the results obtained by investigating about the effect of a seismic action, geographical feature and ground structure, material properties, etc. on the failure of embanked ground and natural slope generated in Nakadori area and Iwaki area of Fukushima prefecture. As for the damage of the developed land, the geographical feature occurred at the valley filled embankment and the embankment reclaimed on the water pond. The material properties of the land for housing lots at Fushiogami of Fukushima is volcanic cohesive soil and the properties at the other land is fine sand with non-plastic. The common feature is found with the flow failure of the embankment with volcanic sand generated in Tohoku district on the recent earthquakes. Either the landslide or the failure of natural and cut slope occurred mostly in the southern part area of Nakadoori district. The landslide has the moving body which consists of unbounded pyroclastic sediments, and failure generated on the surface of the slope with the pyroclastic flow sediment which is the bedrock in this area. The failure mechanism of landslide is a compound slide which has more than two slip surfaces. The upper part of the landslide is caused by progressive failure due to the strong earthquake motion. The lower part of slide is generated by the reduction of the shear strength.

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The 2011 Tohoku-Pacific Ocean earthquake caused severe liquefaction in three lowlands in Chiba Prefecture. In artificially reclaimed lands along Tokyo Bay, liquefaction occurred in a very wide area. Total liquefied area was about 39 km². More than 10,000 timber houses, many lifelines and roads were seriously damaged. Especially the damage in Urayasu City was very severe. Though recorded maximum surface accelerations were not high as about 160 to 230 cm/s², severe liquefaction occurred. Main reason must be due to very long duration of shaking and a big aftershock which occurred 29 minutes after the main shock. Moreover much eruption of sands and large ground subsidence occurred in the liquefied zones because liquefied soils were very fine sand or silt. In the lowland along Tone River, liquefaction occurred at many old river channels. Especially the damage in Katori City was severe. About 2,600 timber houses were damaged. In Kujyukuri lowland plain along Pacific Ocean, liquefaction occurred at the replaced sites where the grounds had been excavated to take iron sands.

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Around 14:46 on March 11, 2011, a magnitude 9.0 earthquake, the largest in our country’s history was recorded off the coast of the Sanriku area in the Tohoku region. A seismic intensity of 7 was observed in Kurihara, Miyagi Prefecture and strong tremors were felt in a wide area from the Tohoku to Kanto region, A maximum seismic intensity of 6.3 was observed at Mito-Minami IC on the Kita-Kanto Expressway. After the quake, emergency inspections were carried out on expressways and it was identified that damages may obstruct traffic on 20 routes for some 870 km. However, owing to the efforts of officials and worker, Tohoku Expressway, Joban Expressway and Ban-etsu Expressway, were opened to emergency vehicles by 11:00 a.m. on March 24, about 20 hours after the earthquake. And Tohoku Expressway was completely opened, except for a few sections, at 6:00 a.m. on Marth 24, 13 days after the quake. This paper reports on the damages and recovery of the earthwork portion of the expressways affected by “The Off the Pacific coast of Tohoku Earthquake”.

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The railway structures suffered severe damages over the wide area by The 2011 off the Pacific coast of Tohoku Earthquake. Although embankments and cuttings of conventional lines suffered damage due to the ground shaking in JR East railway lines, each scale of damages were slight. The maximum length of the embankments damages was about 120m. The tunnels of the Shinkansen and conventional lines suffered little damage. The extensive liquefaction along Keiyo Line caused no damage of railway viaducts and bridges. The tsunami triggered by the earthquake caused catastrophic damage of embankments. The embankment and cutting on 5 railway segments along the coast sustained damages at 50 sites, the forms and scales of the damage varied by the existence of the tide embankment for tsunami and viaduct bridge adjacent to railway embankment.

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A slope failure occurred at an embankment in a residential area in Fukushima City during the 2011 off the Pacific coast of Tohoku Earthquake. In this study, to estimate strong ground motions at the site with high accuracy, aftershock observation was conducted at the site. At the same time, two improvements were made for the site-effect substitution method. One of them is the consideration of the effect of soil nonlinearity on the site amplification factor during the main shock. The other is the consideration of the contributions from two subevents for the main shock ground motion. The estimated seismic waveforms at strong motion stations with the improved version of the site-effect substitution method are very consistent with the observed ones, indicating the validity of the method. Finally, the improved method was used to estimate strong ground motions at the damaged site.

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Ibaraki University, College of Engineering at Hitachi-city, Ibaraki has had a lot of damage due to 2011 off the Pacific coast of Tohoku Earthquake. The authors in Ibaraki University, Geotechnical laboratory have investigated the huge damage due to the above earthquake in Ibaraki prefecture and Iwaki-city, Fukushima. This article has reported the results of investigation about the huge damages. It also clarifys the problems on environmental geotechnics caused by 2011 off the Pacific coast of Tohoku Earthquake, and discusses the direction to solve geoenvironmental engineering issues by simple experiments and preconsideration.

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The severe seismic damage to the large scale filled-valley residential area in Sendai City was caused by the 2011 off the Pacific coast of Tohoku Earthquake. First, this report shows the result of seismic damage research in the filled-valley residential area (called Nankodai) in Sendai City. Next, the result of seismic damage research is arranged paying attention to geographical factor, and the influence of the angle of old topography, the angle of ground surface, and the thickness of filled-valley upon the seismic damage is considered. The following results were obtained through this research. (1) The ratios per an area of fully damaged house in filled-valley area and boundary area were more than 25 times of that in cutting ground area. (2) About 60 % of fully or half damaged house were caused by ground crack. (3) The ratio of fully or half damaged house to all houses was 3 % in filled-valley area, 5 % in boundary area, and 32 % in filled-valley side a little of boundary area. (4) Ground cracks were classified into 3 types, and it was shown that each type of cracks had been controlled by the angle of old topography, the angle of ground surface, and the thickness of filled-valley.

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The iron sand ore deposits had been excavated and the discarded sand from iron ore production had been backfilled at many mining areas in Asahi City, Chiba Prefecture until the end of 1960s. The backfilled sands were liquefied at various backfilled basins due to the main and/or the maximum after shock of the 2011 off the Pacific coast of Tohoku Earthquake. The behaviors of the liquefied soil at the brinks of the backfill basins were new and classified into three types, such as heave, cave-in and landslide based on victim interviews, visual inspections, topographical surveys and soil investigations. The mechanism of these behaviors was attributed to the relationship between the direction of predominant displacement of liquefied soil and the location of the excavation boundary. Based on the time histories of the pore water pressure buildup obtained from a numerical analysis, the backfilled sand liquefied during the main event at several places and it liquefied during the maximum after shock at the other places, which coincides with the testimonies stated by the victims.

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Destruction of a number of pipes was caused by the liquefaction at the time of the Tohoku Earthquake of 2011. Large diameter pipeline ranging from 1500mm to 2600mm was placed in Fukushima Prefecture, Kumado district. The behavior of a buried pipeline during an earthquake was greatly affected by mechanical characteristics of backfill soil. Damaged length extends for 3 kilometers among the total length of 17.8 kilometers was need reconstruction. The damage was characterized by 1m floating up of pipe, surfacing and displacement of manholes, 0.3m slipping out of pipe joints, separation of manifolds resulting from the liquefaction of the backfill sand during the earthquake. On the other hand, a pipeline installed by using crushed gravel for backfill material was small damage. It is also known that increasing the resistance to liquefaction of backfill is very effective due to decrease the damage of buried structure during the earthquake.

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Due to the Tohoku Region Pacific Coast Earthquake occurred on March 11 2011, necessity of countermeasures to liquefaction for detached houses has been increasing in Japan. In this paper, by focusing on ground condition of detached houses damaged by liquefaction, method of the conventional liquefaction judgment was verified using both the Swedish Weight Sounding test and Cone Penetration test results of 86 sites. In addition, based on 160 cases of damaged detached houses with ground reinforcement, the relationship between damage level and inclination angle of detached houses, and applied retrofitting methods was investigated. Finally, we introduced an appropriate ground reinforcement system to liquefaction and the suitable design method.

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Large-scale liquefaction of reclaimed ground occurred in Urayasu city, Chiba prefecture during the 2011 off the Pacific coast of Tohoku Earthquake, causing severe damage to infrastructure of many kinds. However, slightly damaged areas also occurred where soil improvement had been performed. The difference of soil properties between liquefied and non-liquefied areas is interesting for assessment of liquefaction resistance against strong earthquakes. Therefore, the portable cone penetration test and the surface wave method, which are easily conducted immediately after an earthquake, were done at several locations in Urayasu city to estimate the cause of liquefaction and the effects of soil improvement. Finally, a simple ground investigation method is proposed to identify high-risk areas of liquefaction and to determine emergency measures.

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We investigated the failure mechanism of stone wall of Sendai castle. We mainly used a new type of Swedish Weight Sounding testing apparatus in order to evaluate the inner layer structure of ground behind of the stone wall. As a result, the failure of the stone wall seemed to occur since the failed part of the stone wall was constructed on relatively deep embankment. On the other hand, the non-failed part of the stone wall was set on more steady ground. We also used a three dimensional laser scanner to evaluate the total profile of the stone wall itself, side strip and road surface in front of the stone wall as most as correctly. We could grasp the current total profile of stone wall correctly and will be able to use the data for the deformation monitoring in future.

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The great east Japan Earthquake hit Japan on 11 March 2011 and triggered extremely destructive tsunami waves. Field investigation and soil test for its chemical analysis were conducted in Rikuzentakata city of Iwate prefecture on 30the June and 1st July, 2011 as the second investigative team in Kyushu Chapter of JGS. This city was one of the major affected areas by the tsunami. It was reported that this huge sea water had tremendously affected the various geo-environmental problems such as ground settlement, waste materials and agricultural land damaged by sea water. It was also introduced that an innovative approach has been taken to restore the saline soil by using compost containing Halo bacteria.

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Result of the investigation on geotechnical damage to river dikes along the Naruse River and the Yoshida River, Miyagi prefecture, from April 3 to 5 is reported focusing on soil liquefaction. Soil samples were collected from 14 sites where sand boils were observed. Liquefaction occurred at the natural ground such as old river bed or fill material to fill the old river channel. There found correlative relationships between the 50% diameter D₅₀ and the distance D from the river mouth, and between the uniformity coefficient U and D; D₅₀ decreases and U increases as D becomes smaller.

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Numbers of river dikes were damaged by the earthquake motion and tsunami in 2011 off the Pacific Coast of Tohoku Earthquake. This paper summarizes the damages on river dikes in middle and southern coastal part of Iwate Prefecture, with the intention of obtaining physical properties of embankment materials to mitigate the damage on river dikes due to tsunami. Damage configurations such as erosion and collapse were investigated along some rivers in the region of tsunami run up from the estuary. The spots, shapes, soil materials and the damage configurations of the river dikes are highlighted. Damages on embankments at the crossing with road bridges or railway bridges were also surveyed. These investigations have revealed that the river dikes protected with concrete facings will suffer less damage, and that even the three-face-armored banks will be subject to erosion in the upstream of the structures such as abutment or water gate.

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On March 11^th, 2011, the Pacific coast of Tohoku Earthquake hit east Japan. The earthquake-induced liquefaction caused severe damage to residences and buried lifelines in Tokyo bay area. This report summarizes result from field investigation including SWS test in Urayasu city, Chiba prefecture. Grading analysis was also conducted on in situ samples and boiled sands which were retrieved at liquefaction sites. From these investigations, this report shows the liquefaction characteristic causing the wide range of serious subsidence in reclaimed area in Urayasu city. Comparing with the result of investigations in Christchurch city, New Zealand which has suffered the damage of re-liquefactions by the 2010-2011 Canterbury Earthquake, the possibility of re-liquefaction in Urayasu is discussed in this report.

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The 2011 off the Pacific coast of Tohoku Earthquake of Mw=9.0 with a huge source region of about 500km by 200km caused extensive damage of various structures. Damage caused by tsunami was tremendous and a lot of lives were lost. Besides the damage of concrete structures, seawalls were seriously damaged probably due to scouring. On the other hand some reinforced soil walls were found to be damaged little, though they were inundated with tsunami. Such reinforced soil walls are introduced in this report. One has concrete facing panels and the other tree have metal mesh facing panels. They were not seriously damaged with limited sucking out of backfill owing to vegetation and protection sheet. However, some damage was found at the backfill and facing panels where the soil was not properly covered and protected against erosion.

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An evaluation of soil liquefaction risk considering the soil investigation locations is applied to 12km long irrigation channel. The paper provides full procedures of geotechnical reliability analysis that include statistical analysis of site investigation data for site characterization, estimation of soil parameters from site investigation results. Liquefaction potential was modeled by the local estimation in addition to the general estimation that had been generally done. In addition, the liquefaction risk of an arbitrary point was evaluated by the reliability analysis on the liquefaction potential. It was shown that the reliability analysis by the local estimation was an effective method to the countermeasure plan to liquefaction on linearly structure.

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From 3 p.m. to 6 p.m. on July 16th, 2010, a heavy rainstorm of 173 mm (at Oto precipitation station) suddenly attacked in Shobara city, Hiroshima Prefecture. The landslides and the mud flows over 200 sites were caused in a narrow mountainous area of 4 kilometers square by the concentrated heavy rain. It was found that, by the field survey, a typical pattern of slope failure in this disaster is a collapse at the middle portion of plane slope with any trace of valley. In this study, a site investigation including a lightweight dynamic cone penetrometer was carried out at a site of collapse at the middle portion of plane slope. parallel slope. Further, the laboratory tests of soil samples, slope model experiment and stability analysis were conducted to explain the collapse. It is known that there is Kuroboku layer which has a low permeability on the weathered rhyolite layer at the middle point of the slopes, and the slope failures took plane at the boundary of two layers. The result of model slope experiment showed that Kuroboku layer prevented the groundwater flow making the groundwater level rise at the middle of the slope. The safety factor obtained by the slope stability analysis was close to 1.00, when the groundwater level rises to the ground surface.

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In performance-based seismic design, the evaluation of the expected deformation is often requested. In these cases, it is necessary to appropriately estimate the strain increase in the ground from small strain to large strain. In this paper, based on the laboratory test results with various relative densities and fine contents, a practical strain increase mode is proposed. The proposed model is a bi-linear type with different strain increase rate before and after the occurrence of liquefaction. The parameters in the model can be determined from relative density and fines content. The proposed model is beneficial for the accuracy evaluation of the input parameters for numerical simulations.

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The Sand Compaction Pile Method (SCP) is a major method to improve soft clay ground. Natural sand is generally used as a filling material of SCP. In this study, the seismic deformation behavior of improved ground using solidified iron and steel slag as an alternate material was investigated. As a result of the cyclic loading tests using hollow cylindrical torsional test apparatus to composite ground consisting of improvement pile and clay, the dilatancy properties significantly appeared in improvement pile. As a result of dynamic centrifuge model tests, deformation behavior was similar in the case using solidified iron and steel slag and the case using sand, and residual deformation in the improvement area of the case using solidified iron and steel slag is smaller than that of the case using sand. And as the results of effective stress analysis to the model test, it has been confirmed that the consideration of the dilatancy properties of solidified iron and steel slag is important in the seismic performance evaluation.

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In order to investigate the long-term characteristics of the granulated blast furnace slag in the field, the in-situ lightweight embankment was constructed. The changes of physical and mechanical properties that result from latent hydraulic properties were examined in the field measurements and laboratory tests on specimens taken from test site. Following conclusions were obtained: (1) GBF-slag keeps the enough lightweight characteristics over 7 years after construction. (2) Cohesions of GBF-slag increase with time and converge to the constant value after passing 7 years. Latent hydraulic properties of GBFS-slag, however, have little influence on the internal friction angle. (3) The permeability of the GBF-slag after solidification is around 10^-4 - 10^-5m/sec.

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It was known that a part of clayey seabed show a remarkable reduction in water content, increase of shear strength and the washout of fine contents under strong waves. A series of wave loading tests was carried out and the stability analysis was adapted to evaluate the stability of the seabed. It was found that the occurrence of crack is clearly related the property change of seabed, and that the safety factor was calculated by the stability analysis of circle slide with the yield stress of seabed as the strength gave a good explanation on the instability of seabed.

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Pre-bored piling method using nodular pile (precast concrete pile) consists of pitching the nodular pile into soil cement formed by mixing and agitating cement slurry and soil. Formulae for estimating vertical bearing capacity determined from the ground around the pile have been proposed based on the results of many loading tests. For vertical bearing capacity to develop, the soil cement has to transmit the load acting on the nodular pile to the ground. In this study, load test of nodular pile and soil cement in base bulb was carried out to clarify the adhesion effect. From the examinational results, the peak load of nodular pile was 4 times larger than the peak load of straight pile; it was found out that adhesion of nodular pile and soil cement is large effect. It was found out that the bearing pressure of nodular was 2 times larger than the unconfined compression strength of soil cement.

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Oh-hara dam was constructed as the center core type fill-dam for irrigation in 1953. About 55 years has passed when the dam was repaired, as reported in this paper. The safety inspection of the embankment indicated that the embankment was insufficient in the stability during earthquake, and the leaking was developed at the crest by aging.
This paper presents a case study of Oh-hara dam rehabilitated for the seismic resistant-reinforcement and leakage control of the embankment by a cement-mixed soil. The zoning for rehabilitation consisting of upstream and downstream buttress random zones and the center core zone at the crest was designed to fit in the original embankment. The muddy soil that added the soil excavated from the original embankment to the mud in reservoir at the rate of 1: 1.5 by volume was utilized for making the cement-mixed embankment soil. As the result, the excavated soil produced under construction was used up effectively as the embankment soil without the disposal at outside of dam site, and the reservoir capacity of about 30,000m³ was increased in addition to removing the mud in reservoir of about 26,000m³.

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