Ministry of Public Safety and Security

A focusing event that persuades the public, the government, and the media to significantly alter their currently held norms and perceptions comes along rarely; however, when they do, they move mountains. There are many types of focusing events, like the 2001 terror attack on the city of New York, and these types greatly change how life and government organizations move forward. For Disaster Risk Management (DRM) policy, focusing events unfortunately do move us one step closer to a safer society. Therefore, to better understand what events could be constituted as focusing events, in Korea, between the years 1948 and 2015, we analyzed the public, governmental, and media motions after major disaster events to help define a potential focusing event and to see how they distributed along the power law. Once we did that, we are able to definitely conclude which disaster in Korea can be labeled real focusing events for further analysis.

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불포화토에는 부(-)의 압력인 석션(Suction)이 작용한다. 석션은 입자간 응력을 증가시키며, 이에 따라 토립자 골격의 항복응력 및 소성전단강성을 증대시킨다. 따라서 본 연구에서는 이러한 석션의 효과를 지진 등의 동적 하중조건에서 고려하기 위해 불포화토에 대하여 확장된 반복탄소성구성식으로부터 제1 항복함수 및 제2 항복함수를 고려하여 유도된 응력-변형률 관계를 이용하여 반복삼축시험의 요소 시뮬레이션을 수행하였다. 그 결과 응력경로, 응력-변형률 관계 및 체적변형률-축변형률 관계로부터 요소 시뮬레이션은 반복삼축거동을 양호하게 모사함을 확인하였다. 본 연구결과는 동적 하중이 작용하는 불포화토 거동 예측의 정확도 제고에 기여할 것으로 전망된다. Suction affects the unsaturated soil as the negative pore pressure, and leads to increases of the yield stress and the plastic shear stiffness of the soil skeleton due to the growth in interparticle stress. Hence, in this study, in order to account for these effects of suction under the dynamic loading condition such as the earthquake, the element simulation of the cyclic triaxial test using induced stress-strain relation based on cyclic elasto-plastic constitutive model extended for unsaturated soil considering the <TEX>$1^{st}$</TEX> and the <TEX>$2^{nd}$</TEX> yield functions was conducted. Through the stress path, stress-strain relation and relation between volumetric strain and axial strain, it was seen in all the cases that the simulation results demonstrated a good agreement with the experimental results. It is expected that the results of this study possibly contribute to the accuracy improvement on the prediction of unsaturated soil behavior under the dynamic loading condition.

In order to reduce damage by landslides, an early warning system can be one of the effective countermeasures based on the early detection of landslide occurrence and, therefore, preemptive early evacuation of residents from a landslide prone area. Early detection of landslide indication in a broad natural terrain can be performed by monitoring of rainfall in real time or in near-real time. Based on the real time rainfall data, this study suggested a method to warn of landslides by the application of a tracking line of rainfall. The method makes it possible to set up warning criteria of landslides considering local rainfall characteristics in the summer. This study suggested a method of landslide early warning based on the regional rainfall conditions.

In this study, loss with time of dredged sea sand in a tidal embankment subject to sea level variation was examined through the centrifugal model test. The experimental results demonstrate that a differential subsidence occurs on the surface of the dredged-sea-sand fill and that the largest subsidence was observed just above the damaged portion of the geosynthetic mat. In addition, image analysis provided the largest displacement vector at the damaged portion of the geosynthetic mat, the shear-strain localization from the damaged portion of the geosynthetic mat through the center of the slope surface, and the crest of the dredge-sea sand fill. These displacement vectors and shear strains occurred early in the experiment and increased over time. Therefore, the loss of dredged sea sand can occur rapidly with damage to the geosynthetic mat and can possibly induce differential subsidence and cracks at the surface of the dredged-sea sand fill.