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Rasouli R.,University of Tokyo | Towhata I.,University of Tokyo | Hayashida T.,Fudo Tetra Corporation
Physical Modelling in Geotechnics - Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014 | Year: 2014

Subsidence of surface structures has been seen during earthquakes in liquefaction prone areas since many years ago. To date no reliable measure against this problem with reasonable cost has been proposed to people. In this study a series of 1-g shaking table tests have been conducted to evaluate performance of possible mitigations. These experiments concerned lowering of ground water level and installation of sheet-pile walls around the foundation. As expected from case histories records, lowering of ground water level could reduce subsidence of model structure. It is found out that installing sheet-pile walls along with lowering water level can stop settlement completely. In contrast, using sheet-pile walls with open spaces (for cost reduction) between sheets can even increase the magnitude of settlement. Other interesting finding of this series of experiments is the role of formation of water film in post-shaking subsidence of structures. © 2014 Taylor & Francis Group. Source


Yasuda S.,Tokyo Denki University | Harada K.,Fudo Tetra Corporation | Ishikawa K.,Tokyo Denki University | Kanemaru Y.,Kyushu Branch
Soils and Foundations | Year: 2012

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. Source


Otsubo M.,Imperial College London | Towhata I.,University of Tokyo | Hayashida T.,Fudo Tetra Corporation | Liu B.,University of Tokyo | Goto S.,University of Tokyo
Soils and Foundations | Year: 2016

The 2011 off the Pacific Coast of Tohoku Earthquake caused significant damage to embedded lifelines in the Tokyo Metropolitan area. In particular, the floating of embedded sewage pipes and manholes was widely observed on recently constructed artificial islands, where liquefaction took place both in loose backfill soils and the surrounding subsoil. This problem should be addressed in earthquake-prone regions where future earthquake risks are a concern. Thus, the aim of the present study is to develop new backfilling methods using recycled or economical materials to mitigate the liquefaction-induced floating of sewage pipes. The examined recycled materials were crushed glass, crushed concrete, a mixture of tire chips and sand, and cement-treated liquefaction ejecta. Several series of shaking model tests were conducted to investigate the performance of the recycled backfill materials. The proposed methods are to be used when old or damaged pipes are replaced by new ones where the excavation of backfill soils is required. The influence of liquefaction in the surrounding subsoil on the performance of improved backfills constructed of recycled materials was also taken into account. The model test results showed that the examined materials are useful for mitigating the liquefaction-induced floating of buried pipes irrespective of the liquefaction potential in the surrounding subsoil. The importance of balancing the unit weight of the backfilling materials and the surrounding subsoil was highlighted for enhanced safety when the surrounding subsoil was liquefiable. In particular, crushed glass showed the most promising performance for preventing pipeline damage caused by liquefaction. © 2016 Japanese Geotechnical Society. Source


Yasuda S.,Tokyo Denki University | Harada K.,Fudo Tetra Corporation
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

In Japan, many remediation methods against liquefaction have been developed since the 1964 Niigata Earthquake, which caused severe damage to structures due to liquefaction. The methods are classified into two categories: ground treatments to prevent liquefaction, and measure that strengthen structures to prevent or minimize damage if the ground liquefies. The remediation methods have been applied to many kinds of structures, such as oil tanks, quay walls, bridges and buildings. The effectiveness of ground treatments to prevent liquefaction has been proved during past earthquakes. However, a new problem was raised during the 1995 Hyogoken-nambu (Kobe) Earthquake because recorded accelerations were far greater than the design acceleration. Then, studies on the adoption of performance-based design started. The 2011 Great East Japan (Tohoku) Earthquake demonstrated the need for a new concept of measures to prevent liquefaction in areas encompassing houses, roads and lifelines. One of these measures is lowering the ground water table. The applicability of this measure has been confirmed by in-situ tests and analyses, and lowering work started in several cities in 2013. Source


Rasouli R.,University of Tokyo | Towhata I.,University of Tokyo | Hayashida T.,Fudo Tetra Corporation
Soil Dynamics and Earthquake Engineering | Year: 2015

Settlement of surface structures, which is particularly a private house, due to subsoil liquefaction is not a new issue in geotechnical engineering. It has been happening during earthquakes in liquefaction-prone areas since many years ago. However, to date no reliable measure against this problem with reasonable cost has been proposed to people. In this paper, results of a series of 1-g shaking table tests which have been conducted to evaluate performance of a possible mitigation against this problem are presented. The proposed mitigation herein is installation of sheet-pile walls around the foundation. In order to reduce the cost of mitigation, sheet-piling with gap and half-length sheet-piling were examined. The experiments were conducted in different ground water levels. It is found out that installing sheet-pile walls in relatively low ground water level can stop settlement of structures completely. Sheet-piling with gaps delays initiation of settlement but it may increase the ultimate settlement of structure. In addition, it is found that formation of a water film under the building[U+05F3]s foundation is the governing mechanism of post-shaking settlement of structures. © 2015 Elsevier Ltd. Source

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