토석류의 유변물성과 강우재현주기를 고려한 건물의 물리적 취약성 평가

Abstract

The continued increase in population and resulting demand for resources has led to pressures to settle in places where continuous land development processes become a risk. Human lives and structures located in debris flow-prone mountainous areas are commonly subject to debris flow hazards. Previous research into debris flows has mainly focused on landslide hazard mapping and the corresponding triggering mechanisms; however, there is an increasing interest in researches on risk assessment. For a risk assessment, vulnerability assessment for the elements at risk in debris flow is required. Few studies have been made on the vulnerability assessment of a building due to debris flow in spite of the possibility to provide useful information on management of vulnerable areas, prioritization of national disaster management policies, and future city planning. This study presents the physical vulnerability assessment of buildings impacted by debris flow. To achieve the objective, the following works were implemented.

First, the physical vulnerability was obtained from the relationship between the degree of building damage and the intensity of the debris flow events. Three different vulnerability curves were obtained, which are functions of the debris flow height, flow velocity, and impact pressure, separately for different structural types of buildings. Regarding to the non-RC buildings, complete destruction occurred with impact pressures of greater than 30 kPa. For the case of RC buildings, slight damage occurred with impact pressures of less than 35 kPa. The impact pressure of debris flow corresponding to slight damage to an RC building resulted in complete destruction of non-RC buildings. The vulnerability curves of the non-RC buildings increased with increasing flow depth, flow velocity, and impact pressure more rapidly than those of the RC buildings. This means that different structural types of buildings showed different vulnerability curves and damage patterns.

Secondly, large vane-type rheometer developed for measuring the rheological properties of the coarse soil. Several series of rheometer tests were performed to investigate rheological properties of natural soil sample from debris flow disaster area with various water contents. The yield stress and viscosity of weathered soil samples decreased as the water content increased. The water content in soil contributes to reduce yield stress and viscosity, and this is a major cause for a larger run-out distance of debris flow. Water content corresponding to the same yield stress and viscosity shows a different range for each sample. The yield stress and viscosity of the weathered soil obtained through experiments showed a high correlation between the fines content of soil. The estimated rheological properties of weathered soil were used as input parameters for numerical simulation of debris flow.

Third, volumetric sediment concentration of debris flow in risk areas were evaluated using the hydrological theory and IDF curves. Also, initial volumetric sediment concentration of debris flow evaluated the using the flow test. Through this, analysis method of debris flow based on rainfall return period was proposed. In conjunction with a volumetric sediment concentration and initial volumetric sediment concentration of the debris flow risk areas, it can be determined that debris flow will be occurred or not. Also, in conjunction with a volumetric sediment concentration of the debris flow risk areas and rheological properties of weathered soil, the analysis of debris flow behavior by rainfall return period can be carried out.

Finally, physical vulnerability assessment system was established based on three main research contents(physical vulnerability curves, rheological properties of natural soil, analysis of debris flow based on rainfall return period) of this study. The obtained results of vulnerability assessment were applied in Hwangryeong Mt. region of Busan. For accurate vulnerability assessment, a further study, based on database with more debris flow events and rheological properties is needed. Vulnerability index of a building due to the impact of the debris flow is difficult to estimate because it depends on various characteristics of buildings such as the structural type, shape, position, direction, height and number of windows as well. Despite of the disadvantage and limitations of the present study, the presented approach attempts to propose a method to estimate the vulnerability of two structural types of building. In this way, the proposed approach can increase the knowledge about prospective outcomes of future hazards, thus contributing to the protection of the people and their assets.