• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.38-38
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• 2023

Pleikrong reservoir with a concrete gravity dam that impound more than 1 billion cubic meter storage volume is one of the largest reservoir in Central Highland of Vietnam. Sedimentation is a major problem in this area and it becomes more severe due to the effect of climate change. Over time, it gradually reduces the reservoir storage capacity affecting to the reliability of water and power supply. This study aims to integrate the soil and water assessment tool (SWAT) model with 14 bias-corrected GCM/RCM models under two emissions scenarios, representative concentration pathway (RCP) 4.5 and 8.5 to estimate sediment inflow to Pleikrong reservoir in the long term period. The result indicated that the simulated total amount of sediment deposited in the reservoir from 2010 to 2018 was approximately 39 mil m³ which is a 17% underestimate compared with the observed value of 47 mil m³. The results also show the reduction in reservoir storage capacity due to sedimentation ranges from 25% to 62% by 2050, depending on the different climate change models. The reservoir reduced storage volume's rate in considering the impact of climate change is much faster than in the case of no climate change. The outcomes of this study will be helpful for a sustainable and climate-resilient plan of sediment management for the Pleikrongreservoir.

• Smart Structures and Systems
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• v.30 no.4
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• pp.421-432
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• 2022

Regarding the high significance of correct pan evaporation modeling, this study introduces two novel neuro-metaheuristic approaches to improve the accuracy of prediction for this parameter. Vortex search algorithms (VSA), sunflower optimization (SFO), and stochastic fractal search (SFS) are integrated with a multilayer perceptron neural network to create the VSA-MLPNN, SFO-MLPNN, and SFS-MLPNN hybrids. The climate data of Arcata-Eureka station (operated by the US environmental protection agency) belonging to the years 1986-1989 and the year 1990 are used for training and testing the models, respectively. Trying different configurations revealed that the best performance of the VSA, SFO, and SFS is obtained for the population size of 400, 300, and 100, respectively. The results were compared with a conventionally trained MLPNN to examine the effect of the metaheuristic algorithms. Overall, all four models presented a very reliable simulation. However, the SFS-MLPNN (mean absolute error, MAE = 0.0997 and Pearson correlation coefficient, R_P = 0.9957) was the most accurate model, followed by the VSA-MLPNN (MAE = 0.1058 and R_P = 0.9945), conventional MLPNN (MAE = 0.1062 and R_P = 0.9944), and SFO-MLPNN (MAE = 0.1305 and R_P = 0.9914). The findings indicated that employing the VSA and SFS results in improving the accuracy of the neural network in the prediction of pan evaporation. Hence, the suggested models are recommended for future practical applications.

• Journal of the Korean Geotechnical Society
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• v.26 no.3
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• pp.25-34
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• 2010

In the present paper, a numerical study was carried out to simulate ground expansion induced by an application of pulse discharge technology. Based on laboratory pulse discharge tests, the characteristics of shockwave were investigated, and then the laboratory tests were numerical1y simulated using underwater explosion model implemented in a coupled acoustic-structural finite element analysis. In addition, for clayey soils, the expansion of ground was also studied using soil properties obtained from empirical correlations with SPT N values. It was found that the calculation results well agreed with the field test results.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.17-24
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• 2008

In this study, two-dimensional finite element method has been developed to simply consider the nonlinear load-settlement behavior of piled raft foundation subjected to vertical loads. The raft is modeled as the plate finite element based on Mindline's theory and the pile is modeled as the proposed simple pile model that is easy to consider the complex nonlinear load-settlement behavior between pile and soil. The developed numerical method has been compared with the settlement data of lab-scaled experiment and numerical solutions to verify that the developed numerical method shows satisfactory prediction for the nonlinear load-settlement of piled raft foundation.

• Structural Engineering and Mechanics
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• v.81 no.1
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• pp.69-79
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• 2022

The dynamic responses of a pier-pile-soil system subjected to a barge/flotilla collision are analyzed. A coupled high-speed train and bridge system with a damaged pier after barge/flotilla collision is established by taking the additional unevenness of the track induced by the damaged pier as the self-excitation of the system. The whole process of a CRH2 high-speed train running on the 6×32 m simply-supported PC (prestressed concrete) box-girder bridge with a damaged pier is simulated as a case study. The results show that the lateral displacements and accelerations of the bridge with a damaged pier are much greater than the ones before the collision. The running safety indices of the train increase with the train speed as well as with the number of barges in the flotilla. In flotilla collision, the lateral wheel/rail forces of the train exceed the allowable values at a certain speed, which influences the running safety of the trains.

• Earthquakes and Structures
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• v.22 no.3
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• pp.277-287
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• 2022

The ancient underground cities are a collection of self-supporting spaces that have been manually excavated in the soil or rock in the past. Because these structures have a very high cultural value due to their age, the study of their stability under the influence of natural hazards, such as earthquakes, is very important. In this research, while introducing the underground city of Ouyi Nushabad located in the center of Iran as one of the largest man-made underground cities of the old world, the analysis of dynamic stability is performed. For this purpose, the dynamic stress-displacement analysis has been performed through numerical modeling using the finite element software PLAXIS. At this stage, by simulating the Khorgo earthquake as one of the large-scale earthquakes that occurred in Iran, with a magnitude of 6.9 on the Richter scale, dynamic analysis by time history method has been performed on three selected sections of underground spaces. This study shows that the maximum amount of horizontal and vertical dynamic displacement is 12.9 cm and 17.7 cm, respectively, which was obtained in section 2. The comparison of the results shows that by increasing the cross-sectional area of the excavation, especially the distance between the roof and the floor, in addition to increasing the amount of horizontal and vertical dynamic displacement, the obtained maximum acceleration is intensified compared to the mapping acceleration applied to the model floor. Therefore, preventive actions should be taken to stabilize the excavations in order to prevent damage caused by a possible earthquake.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.180-180
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• 2021

가로수는 「도로법」 제11조에 따른 도로(고속국도를 제외한다)와 보행자전용도로 및 자전거전용도로 등 대통령령으로 정하는 도로의 도로구역 안 또는 그 주변지역에 심는 수목을 말하며, 도시의 가로수는 기후조절효과 및 대기오염 정화효과 등을 가질 뿐 아니라 도심지 내에 녹색을 도입하고 도시경관을 구성하는 주요 요소이다. 전국 각 시도에서는 가로수 조성사업을 지속적으로 추진하고 있다. 하지만 몇몇 도시에서는 적절하지 않은 가로수 관리로 인해 가로수가 말라죽는 현상이 증가하고 있다. 이에 가로수 고사 현상을 감소시키기 위하여 토양수분과 토양온도를 측정하여 가로수 피해와 연관성을 조사할 필요성이 있다고 판단하였다. 본 연구는 춘천시에서 진행하였으며, 일반 가로수와 현재 가로수 고사로 문제가 되고 있는 3 모니터링 지점을 선정하고, 토양수분 센서를 5, 15, 40 cm 깊이에 설치하였다. 센서를 이용하여 토양수분과 지온, EC 모니터링을 실시하였다. 토양수분 모니터링 자료를 활용하여 토층별 토양수분 소비량 산정을 하고, 현장 토양시료를 채취하여 물리·화학적 특성을 분석하였다. 또한 가로수 증발산량 산정 및 토층별 토양수분 소비량과 소비패턴을 비교하였다. 본 연구 결과를 향후 RZWQM(Root Zone Water Quality Model) 모델의 기초자료 및 시나리오 구성에 활용될 수 있으며, 모니터링 및 모델링 결과를 활용하여 가로수 및 도시 표토 기능 위협 요인을 분석에 활용 될 수 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.124-124
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• 2020

This study proposes a framework to evaluate extreme drought using the natural drought index and hot spot analysis. The study area was South Korea. Data were used from 59 automatic synoptic observing system stations. The variable infiltration capacity model was used for the period from 1981 to 2016. The natural drought index was constructed from precipitation, runoff and soil moisture data, which reflect the water cycle. The average interval, duration and severity of extreme drought events were determined following Run theory. The most extreme drought period occurred in 2014-2016, with 46 of 59 weather stations exhibition drought conditions and 78% exhibition extreme drought conditions. The Inje and Seosan station exhibited the longest drought duration of 6 months, and the most severe drought was 5 times higher than the extreme drought severity threshold. The hot spot analysis was used to explore the extreme drought conditions and showed an increasing trend in the middle and northeastern parts of South Korea. Overall, this study provides water resource managers with essential information about locations and significant trends of extreme drought.

• Geomechanics and Engineering
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• v.34 no.5
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• pp.561-575
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• 2023

This study investigates to provide a fast solution to the problem of bearing capacity in layered soils with easily obtainable parameters that does not require the use of any charts or calculations of different parameters. Therefore, a hybrid approach including both the finite element (FE) method and machine learning technique have been applied. Firstly, a FE model has been generated which is validated by the results of in-situ loading tests. Then, a total of 192 three-dimensional FE analyses have been performed. A data set has been created utilizing the soil properties, footing sizes, layered conditions used in the FE analyses and the ultimate bearing capacity values obtained from the FE analyses to be used in multigene genetic programming (MGGP). Problem has been modeled with five input and one output parameter to propose a bearing capacity formula. Ultimate bearing capacity values estimated from the proposed formula using data set consisting of 20 data independent of total data set used in MGGP modelling have been compared to the bearing capacities calculated with semi-empirical methods. It was observed that the MGGP method yielded successful results for the problem considered. The proposed formula provides reasonable predictions and efficient enough to be used in practice.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.163-171
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• 2006

The behaviors and design procedures of building excavation plane in innovative prestressed support (IPS) system are presented in this paper. Determination procedure for initial pretension in IPS wale subjected to design earth pressure is derived. The computer analysis model under uniform and non-uniform earth pressure is constructed using beam element for the IPS wale, tension-only element for cable, and compression-only element for soil. Axial forces and bending moments of IPS wale under initial pretension and design earth pressure are calculated. The combined stresses due to these axial force and bending moment are calculated and safety condition of building excavation plane is investigated.