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Sattar A.,University of Tokyo | Konagai K.,University of Tokyo | Kiyota T.,University of Tokyo | Ikeda T.,TOBISHIMA Corporation | Johansson J.,Norwegian Geotechnical Institute
Landslides | Year: 2011

The Hattian landslide, which was triggered by the 2005 Kashmir earthquake, formed one of largest landslide dams in the world and it has posed a serious threat of flooding to people living in the lower reach of the Jhelum River. In order to understand deformation occurring in the body of the dam, physical measurements using a Differential Global Positioning System (DGPS) were conducted. Gradual deformation and slowly developing backward erosion initially were observed, leading eventually to a sudden creation of a deep hollow on the downstream slope of the landslide dam. The dimensions of this eroded gully were determined by laser scanning, and the results showed a significant loss of soil volume and a large change in the body of the dam. A breach formation model was used to predict the outflow hydrograph generated by constant downcutting of dam during a breaching event. A run-off analysis of the outflow hydrograph was conducted to evaluate inundation levels of flood waves in case the dam is breached. Hazardous downstream locations were identified near the junction of the Karli and Jhelum Rivers, suggesting a need for early warning system in order to avoid loss of lives. © 2010 Springer-Verlag. Source

Takase Y.,Chiba Institute of Technology | Ikeda T.,Chiba Institute of Technology | Suzumura T.,TOBISHIMA Corporation
COMPDYN 2015 - 5th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering | Year: 2015

In Japan many buildings that were designed by the old code have been retrofitted structurally because lots of buildings designed by the old code were collapsed in the Southern Hyogo prefecture earthquake in 1995. Moreover many retrofitted structures were subject to strong seismic motion in the 2011 off the Pacific coast of Tohoku Earthquake. It was found that seismic retrofitting was very useful for seismically weak structures. In Sendai city, there is the 10-story residential building that was retrofitted using a passive seismic control system with an amplifier mechanism. The nonstructural members (partial walls) of the building had been damaged when Tohoku Earthquake, though their structural members had not been damaged. In order to evaluate the effect of the seismic retrofitting, we investigated the damage of the building after the 2011 off the Pacific coast of Tohoku earthquake. In addition we calculated the story drift angle by seismic response analysis to evaluate from the analytical viewpoint. As a result of the damage investigation of this building, it was obvious that the building was safe structurally. Furthermore, we verified when nonstructural members had been in failure using the modified compression field theory(Vecchio, F.J. and Collins, M.P, 1986). The nonstructural members were in failure before the peak acceleration. Thus, we concluded that the effect of the partial walls on structural performance was very small. Source

Ikeda T.,Chiba Institute of Technology | Takase Y.,Chiba Institute of Technology | Senoo Y.,TOBISHIMA Corporation
COMPDYN 2015 - 5th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering | Year: 2015

A steel frame reinforced concrete building completed in 1965 was seismically retrofitted using seismic isolation braces with amplification mechanism. The building was subjected to shaking with a seismic intensity of upper 5 during the 2011 off the Pacific coast of Tohoku Earthquake. The seismic retrofit applied, however, minimized damage. The seismic retrofit performance was then examined based on the ground motions recorded in the building and the results of seismic response analysis using the records. As a result, it was revealed that the retrofit design goal was met and that the deformation of the building was controlled considerably as compared with the case with no retrofit. Source

Kiyota T.,University of Tokyo | Sattar A.,University of Tokyo | Konagai K.,University of Tokyo | Kazmi Z.A.,University of Tokyo | And 2 more authors.
Soils and Foundations | Year: 2011

On February 9 2010, the landslide dam formed in the Kashmir earthquake that occurred on Oct 8 2005 at Hattian Bala in Pakistan was breached after incessant rains. The authors had been involved in a research project to monitor the long-lasting change of the landslide mass at regular 6 monthly intervals since June 2008, and they noticed that air-exposed pieces of sandstones and mudstones of the landslide mass had disintegrated and crumbled due to slaking that dated back to the breach. The change in the landslide mass shape observed between June 2008 and November 2009, did not seem so significant except for a 300 m-long gulley that appeared all of a sudden at the toe of the mass during winter time from 2008 to 2009. Displacements from GPS-measurements conducted in June and November 2009 showed that the crest part subsided by about 10 cm while the toe part heaved slightly up where the overflowed water fell into the eroded gully. A field survey was conducted over the breached landslide dam in April 2010, two months after the breaching event. A severely eroded breach channel was observed along the spillway, which was excavated immediately after the formation of the dam. Given the chronological change in precipitation of the catchment area of Hattian Bala obtained from the TRMM (Tropical Rainfall Measuring Mission) satellite data, the dam is considered to have been breached due to the overtopping of water over the landslide mass of slakable nature. The slakable nature of the material is discussed through both standard slaking tests and advanced unconventional direct shear tests on prepared specimens. Significant creep deformation and a reduction in their peak strength were observed as the slaking developed in the specimens, suggesting that the slakable nature of the mudstones might have been responsible for the breach of the landslide dam. Source

Kumagai K.,Tobishima Corporation Head Office | Terashima Y.,TOBISHIMA Corporation | Kanematsu K.,Tobishima Corporation Head Office
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

In soft or squeezing ground, early section closers by means of invert shotcrete and invert concrete are often carried out to restrain deformation and stabilize the ground around the tunnel. However, while advancing the terrestrial face, there is a risk of damage, such as cracking, occurring in the invert due to redistribution of plastic ground pressure and the intrinsic characteristics of the ground. During excavation of the Ozaso Tunnel on the Tohoku Chuo Expressway, ground deformation caused the propagation of numerous cracks in the invert. This paper presents an outline of the investigation into the cracks, the major cause, and the design and construction management of the countermeasure work. © 2014 by Japanese Committee for Rock Mechanics. Source

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