• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.19-30
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• 2022

Developing a fragility curve for the levee requires calculating the probability of failure according to the water level for each failure mode. Since probabilistic analysis requires iterative analysis to account for variability in geotechnical parameters, the fragility curve development inevitably requires many iterative calculations. Therefore, approximate probabilistic analysis techniques are usually applied to reduce the amount of calculation in developing the levee fragility curve. However, their accuracy has not been determined clearly. This study calculated the failure probability of slope and piping failure mode for an actual levee through probabilistic methods, such as FOSM, PEM, and MCS. Then, the fragility curve of the levee according to the water level was developed. The results of the approximate methods: FOSM and PEM, were compared with those of MCS to evaluate the applicability to the fragility curve for slope and piping failure mode.

• Journal of the Korean GEO-environmental Society
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• v.13 no.3
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• pp.13-19
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• 2012

Due to recent climate change, big typhoon and heavy rainfall happen frequently not only in Korea but also all over the world. It leads to collapse of levee by extraordinary flood. It lead to collapse of levees by extraordinary flood. These natural disasters give the life and property damages in near region. In this study, it was performed that a stability in levee using seepage analysis. It has been evaluated hydraulic gradient of exit zone according to variations in levee crest width, gradient. As a result, it showed that hydraulic gradient of exit zone was decreased due to increase of levee crest width and gradient, and it was evaluated that vertical hydraulic gradient was decreased than that of the horizontal hydraulic gradient.

• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.29-41
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• 2018

In the case of the enlargement levee on the soft foundation, the existing levee and the enlargement levee connection can be damaged due to heterogeneous subsidence such as differential settlement at the joint of the box culvert passing through the levee. This study selected the downstream region of the Geum River and then confirmed the influence of the piping possibility on the levee by performing a 2D seepage analysis and analyzing the seepage tendency according to the position of the box culvert's gate. As a result, the flow velocity and the hydraulic gradient are larger in the upper breakage than the lower breakage, and the upper leak was more vulnerable to the piping than the lower leak. If leaks occur in the gate located on the riverside land, the risk of piping is increased when the water level rises and is maintained highly. In the case of the gate located on the inland, it could be predicted that the leakage could damage the stability of levee by increasing the water pressure inside the levee. As a result, if leakage occurs at any position in the box culvert, the pore water pressure is increased or decreased compared with the case when no leakage occurs. Therefore, if the pore water pressure is drastically reduced or increased compared with the normal case, leakage may occur. However, the result of this study is based on a 2D seepage analysis, and it is likely to be different from actual cases. Therefore, more detailed analysis by 3D analysis is recommended.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.269-279
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• 2015

Nowadays, the world has suffered by natural disaster of climate change due to global warming. Korea has also faced with similar situation. To prevent these natural disaster, Four Major River Management has conducted. One of conducted content in Four Major River Management is the levee maintenance which classified into fill-up the inland, levee of reinforcement and so on. These maintenances may make the characteristics of groundwater flow change and affect to the levee safety (piping phenomenon). Therefore, analysis on groundwater fluctuation according to level of riverside and inland should be required. This study focus on levee of Hoe stream, which is connected to Nakdong river, and piping safety factor in the levee analyzed by using pore water pressure. Besides, groundwater fluctuation, which is depended on level of riverside and inland, is simulated by using the SEEP/W (2D ground water model). This simulation considered steady flow and unsteady flow. As a result, piping safety factor increased due to rising the inland level. Piping safety factor of riverside was effected by only river water level. Therefore, external levee factor considering inland level raising and suitable control of river water level is need to increase piping safety factor.

• Journal of Korea Water Resources Association
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• v.48 no.12
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• pp.1077-1087
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• 2015

The levee protect lifes, houses, and properties by blocking overflow of river. The revetment is forced to be covered on the slope of levee in order to prevent erosion. The stability of revetment is very important enough to directly connected to the stability of levee. In this study, the weak points of revetment on meandering channel were found by movable revetment experiment and the velocity and the water surface elevation (WSE) were measured at main points. The 3-D numerical simulations were performed under same conditions with experiment. And unclear flow characteristics by the limit of measuring instruments were analyzed through numerical simulation. Consequently, the section of large wall shear stress and the failure section are almost the same. Despite of small wall shear stress, the revetments located at right bank were carried away because of circulation zone due to secondary flow by meandering. With existing riprap design formula, the sizes of riprap determined using maximum local velocity were 1.5~4.7 times greater than them using mean velocity. As a result of this study, it is necessary to calculate the size of riprap in other ways for meandering and straight channel. At a later study, if the weighted value considered the radius of curvature and shape of hydraulic structure is applied to riprap design formula, it is expected that the size of revetment was evaluated rationally and accurately.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.69-75
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• 2014

The shear strength characteristics of an unsaturated earth material are highly important not only for evaluating the seepage characteristics but also the stability of levee for a lifelong. In this study, unsaturated strength characteristics of Nak-dong river sand and clay that frequently used for the levee construction in southern province of Korea were analyzed using unsaturated triaxial compressive test. The strength characteristics due to the variation of matric suction were analyzed using multi-stage compression technique and the results were directly compared with the non-linear formulation for the apparent cohesion ($C_{max}$), and the friction component ${\varphi}^b$ were determined and evaluated from the test for the application of linear Mohr-Coulomb failure criteria. Cohesion and friction characteristics of the unsaturated levee material under various suction phases were also explored during this study.

• Journal of Korea Water Resources Association
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• v.50 no.4
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• pp.277-288
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• 2017

A probabilistic risk analysis of levee system estimates the overall level of flood risk associated with the levee system, according to a series of possible flood scenarios. It requires the uncertainty analysis of all the risk components, including hydrological, hydraulic and geotechnical parts computed by employing MCMC (Markov Chain Monte Carlo), MCS (Monte Carlo Simulation) and FOSM (First-Order Second Moment), presents a joint probability combined each probability. The methodology was applied to a 12.5 km reach from upstream to downstream of the Gangjeong-Goryeong weir, including 6 levee reaches, in Nakdong river. Overtopping risks were estimated by computing flood stage corresponding to 100/200 year high quantile (97.5%) design flood causing levee overflow. Geotechnical risks were evaluated by considering seepage, slope stability, and rapid drawdown along the levee reach without overflow. A probability-based compound risk will contribute to rising effect of safety and economic aspects for levee design, then expect to use the index for riverside structure design in the future.

• Korean Journal of Remote Sensing
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• v.37 no.5_3
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• pp.1425-1434
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• 2021

Continuous and periodic data acquisition must be preceded to maintain and manage the river facilities effectively. Adapting the existing general facilities methods, which include river surveying methods such as terrestrial laser scanners, total stations, and Global Navigation Satellite System (GNSS), has limitation in terms of its costs, manpower, and times to acquire spatial information since the river facilities are distributed across the wide and long area. On the other hand, the Mobile Mapping System (MMS) has comparative advantage in acquiring the data of river facilities since it constructs three-dimensional spatial information while moving. By using the MMS, 184,646,009 points could be attained for Anyang stream with a length of 4 kilometers only in 20 minutes. Levee points were divided at intervals of 10 meters so that about 378 levee cross sections were generated. In addition, the waterside maximum and average slope could be automatically calculated by separating slope plane form levee point cloud, and the accuracy of RMSE was confirmed by comparing with manually calculated slope. The reference slope was calculated manually by plotting point cloud of levee slope plane and selecting two points that use location information when calculating the slope. Also, as a result of comparing the water side slope with slope standard in basic river plan for Anyang stream, it is confirmed that inspecting the river facilities with the MMS point cloud is highly recommended than the existing river survey.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.191-200
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• 2011

Levee failure cause the huge amount of damage to human and property. Overflow and erosion of levee are primary cause of a break in a levee but the analysis of breach pattern and impact is partially inadequate. The flow characteristics of meandering rivers are very important in field of river hydraulics that should be studied in practical viewpoints relating to river levee. In meandering the secondary flow that rotary direction is changed reciprocally occurs in three dimension is known. In this study flow characteristics of local river are considered and of meandering channels are analyzed using CCHE2D and FLOW3D. The stability and accuracy of models are examined comparing the measuring and analyzed data for the experimental channel and natural river(Namgang). Consequently, the flow characteristics in a meandering river are suggested precisely and it is essential that river levees having meandering river should be analyzed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.679-686
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• 2020

In this study, the seismic vulnerability of public river levees was analyzed quantitatively. Input seismic waves were generated in Pohang seismic waves in return periods of 200, 500, 1000, and 2400 years. The behavior of the levee was analyzed by seismic vulnerability analysis according to the return period. The displacement that occurs during an earthquake showed the same tendency as the input seismic wave and was largest in the return period of 2400 years. An analysis of the sliding stability revealed a 31.5% and 26.7% decrease in the sliding safety factor for the return period of 2400 for the landside and waterside, respectively. An examination of liquefaction by the q/p' ratio showed that the seepage line inside the embankment rises due to earthquakes. As a result, in the case of a return period of 2400 years, most embankments generate liquefaction, making them vulnerable to earthquakes. Through this research, it will be necessary to re-establish domestic seismic-design standards and establish clear standards for the results through a dynamics method.