The 2011 off the Pacific Coast of Tohoku Earthquake that occurred on March 11 brought serious damage to the infrastructure facilities in Tohoku and Kanto districts owing to the strong earthquake motion, tsunami, and nuclear power plant accident. This was referred to as "triple disasters" by a newspaper and was given the name the "Great East Japan Earthquake Disaster" by Cabinet decision. Five years has passed since this disaster occurred. During these five years, restoration works in affected areas have progressed steadily with the aim to make a strong community that is resilient to disaster and restore local life and economic activity. In these activities, civil engineering plays an important role. In particular, the Japan Society of Civil Engineers (JSCE) is considered very important in providing the technical and scientific knowledge necessary for these activities to international societies. In this regard, the JSCE has come out with the second special issue on the Great East Japan Earthquake Disaster. This issue is a valuable collection of papers and reports on various recovery efforts and technological development to achieve the recovery works. Sixteen invited papers and seven general papers are included in this issue. The JSCE takes pride in editing and publishing this second special issue on the Great East Japan Earthquake Disaster. The technical and scientific knowledge and other information on the restoration and recovery works from the natural disaster contained in this issue will be useful for other countries that similarly suffered from earthquake disaster. On behalf of the editorial committee, I wish to sincerely thank the authors, reviewers, and all of the contributors in this special issue.
Special Topic -Division A: Structural Engineering/Earthquake Engineering & Applied Mechanics
Many bridge bearings suffered severe earthquake loads during the 2011 Great East Japan earthquake; however, no suitable technique exists to evaluate damage to laminated rubber bearings. This paper describes the Acoustic Emission (AE) technique for laminated rubber bearings both for damage assessment after earthquakes and health monitoring of old bridges. First, laboratory tests were conducted using the damaged laminated bearing specimens after the pre-loaded tests. Characteristic AE behavior was observed in the severely damaged specimens during the cyclic loading compression tests. These specimens had many small voids in the rubber, which were found from the microscope observation of the specimens being cut after the loading tests. Then, on-site AE monitoring was carried out at two sites. Many AE hits and large AE energy were observed from the deteriorated rubber bearings; however, few AE activities were observed from the new bearings. These two tests indicated the effectiveness of AE monitoring for early warning and damage assessment of laminated rubber bearings.
A number of infrastructures for Sanriku Railway were seriously damaged by the 2011 East Japan Earthquake. In this paper, the damage by seismic loads and tsunamis are analyzed. In addition to serious damage by seismic loading, embankments, RC viaducts and bridges were washed away by the great tsunami in many places. A number of bridges and embankments could be effectively made highly earthquake- and tsunami-resistant by taking advantage of soil-reinforcing technologies. The design and construction in this restoration work took advantage of technologies that had been developed based on state-of-the-art geotechnical engineering, concrete engineering, and bridge engineering while aiming at cost-effective and fast restoration. At Arakawa Bridge, the PCI girder was washed away and a new PC hollow girder with a small height, pier and geosynthetic-reinforced soil (GRS) embankment was installed. In the Shimanokoshi area, as requested by local people, a collapsed RC viaduct was replaced to a seismic- and tsunami-resistant geosynthetic-reinforced embankment covering slopes with concrete facing connected to geogrid layers reinforcing the embankment to prevent erosion of the backfill and scouring at the slope toes. At three places, in place of the collapsed three simple girder bridges, three GRS integral bridges, which are highly earthquake- and tsunami-resistant due to structural integration of reinforced backfill, full high rigid (FHR) facings and a continuous girder, were constructed and opened to service for the first time. In the existing embankments eroded by tsunami, the roadbed was restored by “reinforced roadbed” and embankment slope was covered with cast-in-place concrete facing or RRS (Reinforced Railroad/Road sloped structures with geocells and reinforcing steel bars) method.
In the land reclamation areas of Urayasu City, 8,700 small buildings including residential houses suffered severe damage due to liquefaction during the 2011 Tohoku earthquake. Following this event, Urayasu City adopted grid wall soil improvements as countermeasures to mitigate liquefaction. For the simplified grid wall soil improvement design, the spacing between the grid walls is restricted within L/H = 0.8, where L is the spacing between the grid walls and H is the thickness of the liquefaction layer. However, it is difficult to adopt L/H as a design guideline because the grid wall soil improvement has to be applied underneath existing houses. The construction of grid walls directly underneath houses is impossible. Consequently, the spacing between the grid walls increases. It is suitable to use the settlement of a house as a design guideline for the conditions in Urayasu. Therefore, the following guideline was adopted. For a shock of the same magnitude as that of the main shock in the 2011 Tohoku earthquake in Urayasu no obvious damage must occur to a residential house. To meet this guideline, FL must exceeds 1.0 in all liquefied layers, or the index of settlement Dcy must be within 5 cm and the non-liquefied layer H1 must exceed 5.0 m. The finite element method with a quasi-three-dimensional analysis model can be used to estimate the settlement of houses. However, there are no examples that have adopted the settlement as a design guideline in grid wall soil improvement design. Thus, dynamic centrifuge model tests were conducted to investigate the relationship between the settlement of houses and the grid area. Existing design guidelines for grid wall soil improvement use FL or an excess pore pressure ratio. This study proposes a performance- based design method for grid wall soil improvement and verifies the validity of this approach.
Special Topic -Division D: Infrastructure Planning and Management
In order to examine the economic impact of the damage due to the Great East Japan Earthquake in 2011 and the reconstruction of the disaster-stricken areas and all prefectures, this study aims to develop a dynamic spatial computable general equilibrium model. This model describes the economic dynamics of the damage caused by the earthquake, the resulting reconstructions, and measures the dynamic benefits of reconstruction by using numerical simulations. The findings of this study are as follows: (1) The discounted present value of the dynamic damage cost along with reconstruction from the earthquake was estimated to decrease to about 17.9 trillion yen in total, which was 1.29 times greater than decreases in the direct damage cost of about 13.9 trillion yen in the Tohoku disaster-stricken areas. (2) The damage costs and benefits could be measured more accurately based on the economic theory by introducing the dynamic multiplier of damage costs and benefits into the conventional benefit measurement technique. (3) The forward-looking dynamic model, despite strict constraints and unrealistic assumptions, could show realistic results.
Special Topic -Division E: Materials, Concrete Structures and Pavements
The 2011 Tohoku Region Pacific Coast Earthquake struck off Tohoku and Kanto regions of Japan on 11 March 2011. We conducted investigations of structural and surface damage to pavement in the runway, taxiway and apron at Sendai Airport for the purpose of re-opening the airport for commercial flights. Many cracks were confirmed in the asphalt pavement in the runway and taxiway. However, it was clarified that these cracks except the one in the taxiway were not fatal structural damage that would hinder the provisional use of the airport. Large settlement was confirmed in a part of the asphalt pavement in the taxiway and concrete pavement in the apron due to liquefaction. It was confirmed that these settlement areas needed to be reconstructed for the re-opening of the airport. Furthermore, the effect of the void underneath the cement concrete slab on FWD deflection was clarified.
“Reconstruction Roads” are the highways constructed to accelerate recovery from the Great East Japan earthquake that occurred in 2011. The total distance of Reconstruction Roads is approximately 360 km, which includes more than 250 bridges. Because Reconstruction Roads are located in a cold zone, durability against frost attack is necessary for their concrete structures. In addition to freezing and thawing effects, bridges also suffer from alkali silica reaction (ASR) and chloride attack from the use of deicing salt. During the construction of a reinforced concrete (RC) slab of the “Mukai sada-nai Bridge,” we designed the concrete and reinforcing materials to be durable. A multiple defense strategy is a key phrase in our durability design. To prevent possible deterioration, at least two countermeasures were applied. The use of fly ash is a core countermeasure because it is effective against both ASR and chloride attack. Air content was designed at 6% to achieve antifrost performance. An expansive agent was also used to reduce the risk of shrinkage cracks. Epoxy-coated reinforcing bars were used to resist corrosion. An RC slab was carefully constructed at the Mukai sada-nai Bridge. Wet curing continued for three months to obtain a pozzolanic reaction. The quality of the hardened concrete was checked by element tests and nondestructive tests. Additional costs to enhance durability were acceptable with regard to risk control. Success at the Mukai sada-nai Bridge was followed by the construction of other durable RC bridge decks on Reconstruction Roads.
Special Topic - Division F: Construction Engineering and Management
Evaluating the benefits of disaster mitigation action quantitatively and sharing these results with the society are extremely useful in promoting mitigation action. Many studies, however, have focused on the investigation of the damage but not on the mitigation effects of preparedness. Hence, this study analyzed the mitigation effect of the Business Continuity Plan (BCP) on financial damage to non-manufacturing industries in the Great East Japan Earthquake. Our analysis showed the following: 1) In many companies, there is no difference in the direct damage to the company group with BCP and to the group without BCP. 2) The sales of the damaged group without BCP decreased about 5% compared to those of the damaged group with BCP for more than two years. In other words, the effect of mitigating financial damage by BCP is more than 10% of annual sales on the average. 3) The relationship between BCP and sales was analyzed under limited variables, and the coefficient of BCP showed positive effect on sales with significance at a 5% level. Although our result is only an indication, it could be said that this finding, which shows cost-benefit information on BCP, is useful to promote BCP.
Division D: Infrastructure Planning and Management
This study was conducted to verify the effects of some geometric factors, such as the angular direction change, the available visual information amount, the width variation of streets, and the axis deviation on street space on the continuity of the street network, to have a good legibility along the street. The main purpose of this research is to provide a classification of route types considering the legibility of street space. The experiment was conducted around the Minami Urawa Station in Saitama Prefecture. The street network in the study area was analyzed using two types of parameters, such as visibility parameters and spatial parameters. The visibility parameters were obtained through statistical calculations using visibility attributes defined through a field survey, while spatial parameters were hypothetically defined using the knowledge about the street network of the study area and referring to the literature. Both parameters were analyzed using PCA (Principal Component Analysis) and Cluster analysis to define route types. The results of the research clearly illustrated that there was a significant relationship between the visual characteristics of the street network and the street space legibility. Seven types of routes were classified and their attributes were clarified. These attributes affected the wayfinding behavior of the pedestrians in the study area.