Tadashi Hara

Resilient and Sustainable Geotechnical Solution: Lessons Learned from the 2011 Great East Japan Disaster

This paper first describes the field tests conducted on a tire retaining wall that miraculously survived in the 2011 Great East Japan disaster. The paper then proposes a new concept of using waste tires behind the seawall in order to protect such coastal structures from the damage due to impact force of tsunami. A physical model for tsunami impact force simulation was developed and described to evaluate the reduction effect of tsunami impact force by the tire structures. Finally, from aesthetic point of view, cultivation of suitable plants inside the tires was proposed. Field tests on planting trees that can grow in saline soil conditions were performed to see whether tire structures can preserve the greenery of the area. The results of this research, thus, can go a long way toward providing a sustainable solution for infrastructure development in the future.

Analysis of a Coastal Structure Damaged Due to Compound Effect of Earthquake and Tsunami

This paper analyzes the cause of damage to the Yoshihama river dike located in Ofunato city of Iwate prefecture, which were damaged due to strong shaking of the 2011 off the pacific coast of Tohoku earthquake and subsequent tsunami. Analyses were based on the past field investigations and numerical simulations. Investigations revealed that the dike body had low liquefaction resistance and the volume change after liquefaction was rather large. Two dimensional effective stress analyses showed that due to main shock and aftershock, there is a likelihood of liquefaction in dike body and the reliquefaction possibilities are high even under small ground motion.

Field study on the damages of a well due to the Great East Japan Earthquake

The prolonged interruption of city water supply caused by the Great East Japan Earthquake had severe influences on the daily life of citizens and the economic activities in the quake-hit area. Thus the necessity for alternative water supply system that can complement the existing city waterworks is being recognized. In this study, field tests were conducted on water wells suffered by the compound forces of vibration and tsunami in order to investigate the ground vibration properties, damage in the well structures, and water pumping ability. As a result, no functional losses of the wells were found. This result suggests the technical possibility of constructing an alternative water supply system that utilizes the groundwater as measures against mega-earthquake disaster.