• Geophysics and Geophysical Exploration
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• v.25 no.3
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• pp.120-128
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• 2022

There are 17,000 reservoir dams in Korea, of which more than 85% were built over 50 years ago. Old embankment dams are weakened by internal erosion and suffusion phenomena due to preferential leakage paths and this ongoing weakening can cause their failure. Therefore, early warning associated with leakage in an embankment dam is crucial to prevent its failure. An electrical resistivity survey is a non-destructive, real-time and in-situ technique for detecting the development of leakage zones and general conditions of embankment dams. Because of its advantages, the electrical resistivity survey is widely used for reservoir safety inspections. However, the electrical resistivity survey is still not officially included in the precise safety inspection of reservoir dams because it cannot present a quantitative index of dam safety. In this study, we propose a method for calculating the leak index according to the water content evaluated from the electrical resistivity survey and/or induced polarization survey. Particularly, by proposing a quantitative leak index calculation method from monitoring surveys and independent surveys, we provide a theoretical basis for including electrical resistivity and induced polarization surveys as components of the precise safety inspection of reservoirs dams.

• Structural Monitoring and Maintenance
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• v.9 no.4
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• pp.323-336
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• 2022

Steel truss bridge is one of the most widely used bridge types in Indonesia. Out of all Indonesia's national roads, the number of steel truss bridges reaches 12% of the total 17,160 bridges. The application of steel truss bridges is relatively high considering this type of bridge provides advantages in the standardization of design and fabrication of structural elements for typical bridge spans, as well as ease of mobilization. Directorate of Road and Bridge Engineering, Ministry of Works and Housing, has issued a standard design for steel truss bridges commonly used in Indonesia, which is designed against the design load in SNI 1725-2016 Bridge Loading Standards. Along with the development of actual traffic load measurement technology using Bridge Weigh-in-Motion (B-WIM), traffic loading data can be utilized to evaluate the reliability of standard bridges, such as standard steel truss bridges which are commonly used in Indonesia. The result of the B-WIM measurement on the Central Java Pantura National Road, Batang - Kendal undertaken in 2018, which supports the heaviest load and traffic conditions on the national road, is used in this study. In this study, simulation of a sequences of traffic was carried out based on B-WIM data as a moving load on the Australian type Steel Truss Bridge (i.e., Rangka Baja Australia -RBA) structure model with 60 m class A span. The reliability evaluation was then carried out by calculating the reliability index or the probability of structural failure. Based on the analysis conducted in this study, it was found that the reliability index of the 60 m class Aspan for RBA bridge is 3.04 or the probability of structural failure is 1.18 × 10^-3, which describes the level of reliability of the RBA bridge structure due to the loads from B-WIM measurement in Indonesia. For this RBA Bridge 60 m span class A, it was found that the calibrated nominal live load that met the target reliability is increased by 13% than stated in the code, so the uniform distributed load will be 7.60 kN/m² and the axle line equivalent load will be 55.15 kN/m.

• Tunnel and Underground Space
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• v.33 no.1
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• pp.57-69
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• 2023

In this study, we simulated induced seismicity in the Groningen natural gas reservoir using 2D hydro-mechanical coupled discrete element modelling (DEM). The code used is PFC2D (Particle Flow Code 2D), a commercial software developed by Itasca, and in order to apply to this study we further developed 1)initialization of inhomogeneous reservoir pressure distribution, 2)a non-linear pressure-time history boundary condition, 3)local stress field monitoring logic. We generated a 2D reservoir model with a size of 40 × 50 km² and a complex fault system, and simulated years of pressure depletion with a time range between 1960 and 2020. We simulated fault system failure induced by pressure depletion and reproduced the spatiotemporal distribution of induced seismicity and assessed its failure mechanism. Also, we estimated the ground subsidence distribution and confirmed its similarity to the field measurements in the Groningen region. Through this study, we confirm the feasibility of the presented 2D hydro-mechanical coupled DEM in simulating the deformation of a complex fault system by hydro-mechanical coupled processes.

• Korean Journal of Construction Engineering and Management
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• v.13 no.6
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• pp.13-23
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• 2012

While Category 1 and Category 2 bridges are intensively inspected and carefully managed, many small bridges that are not in the Category 1 and 2 are often forgotten until they decay in serious condition. Since many of these small bridges located in the populated city, failure of them would cause huge negative impact on the community. This paper focuses on the small size concrete bridges for timely repair and rehabilitation work for the effective operation and management. Test bed is developed to define the key parameters to forecast the long term performance of the bridges, mostly concrete box bridges. Key parameters suggested in this paper are cumulative fatigue due to repetitive heavy traffic loads and the acid attacks for concrete material deterioration. The cumulative fatigue is measured by the use of the mileage concept. For the long term data collection and inspection, stable and easy to use data collection system is installed as a test bed. The contribution of this research work is on the development of the test bed to define the key parameters of bridge deterioration.

• Korean Journal of Environmental Biology
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• v.29 no.4
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• pp.373-378
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• 2011

Our aim was to investigate the genotoxicity of ambient air in the Krak$\acute{o}$w area after Fukushima Nuclear Power Plant (NPP) accident and compare with results from Chernobyl fallout. For the detection of ambient air genotoxicity the technique for screening gene mutation frequency in somatic cells of the $Tradescantia$ stamen hairs ($Trad$-SH assay) was used. Since 11th of March 2011 (Fukushima NPP accident), several pots containing at least 15 shoots of bioindicating plants were exposed to ambient air at 2 sites in the Krak$\acute{o}$w surrounding area, one in the city center, and about 100 pots in a control site (in the glasshouse of the Institute of Nuclear Physics) Continuous screening of mutations was performed. Progenies of 371,090 cells exposed were analyzed. Mutation frequency obtained in the first 10 days has shown a mean control level (GMF*100=$0.06{\pm}0.01$). At scoring period related to influence of a potential Fukushima fallout, a significant increase of gene mutation frequencies above the control level was observed at each site in the range, 0.10~0.33 depending on the location, (mean value for all sites GMF*100=$0.19{\pm}0.05$) that was associated with a strong expression of toxic effects. In the reported studies following the Chernobyl NPP accident monitoring $in$ $situ$ of the ambient air genotoxicity was performed in the period since April $29^{th}$ till June $3^{rd}$ 1986 also with Trad-SH bioindicator. In general, mutation frequency increases due to Chernobyl fallout(GMF*100=$0.43{\pm}0.02$) were corresponding to fluctuation of radioactivity in the air reported from physical measures, and to published reports about increase in chromosome aberration levels. Although, recent data obtained from monitoring of the ambient air quality in the Krak$\acute{o}$w and surroundings are lower when compared to results reported after Chernobyl NPP accident, though results express a significant increase above the control level and also are corresponding with increased air radioactivity reported from physical measurements. Statistically significant in comparison to control increase in gene mutation rates and more prolonged than that after Chernobyl fallout increase of GMF was observed during the period following the Fukushima NPP failure.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.5
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• pp.443-451
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• 2013

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect any further growth or expansion of preexisting defects or to characterize failure mechanisms. Recently, this kind of technique, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind turbine blade. In this study, the activities of AE signals generated from external artificial sources was evaluated and located by new developed signal mapping source location method and this test is conducted by 750 kW full-scale blade. And a new source location method was applied to assess the damage in the wind turbine blade during step-by-step static load test. In this static loading test, we have used a full scale blade of 100 kW in capacity. The results show that the acoustic emission activities give a good agreement with the stress distribution and damage location in the blade. Finally, the applicability of the new source location method was confirmed by comparison of the result of source location and experimental damage location.

• Journal of the Korean Geophysical Society
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• v.9 no.1
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• pp.47-62
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• 2006

More than 70% of Korean Peninsula is consisted of mountains, so that lots of roads, rail-roads and tunnel,which play a pivotal role in the industry activity, are existed along the rock-slope and in the rock-mass. Thus,it is urgent that tegration of management system through the optimum survey and design of rock-slope excavation, proper stabilization method and database of rock-slope. However, conventional methods have shortcoming with the economy of survey time and human resources, and the overcome of difficulties of approach to the in-situ rock-slope. To overcome the limitation of conventional method, this paper proposed the development of remote measurement system using Terrestrial Laser Scanning System. The method using Terrestrial 3D Laser Scanning System, which can get 3D spatial information on the rock-slope and2)Dept. Geosystem Engineering, Kangwon National University, Korea tunnel, has an advantage of reduction of measurement time and the overcome of difficulties of approach to the in-situ rock-slope/dam/tunnel. In the case of rock-slope, through the analysis of 3D modeling of point-cloud by Terrestrial Laser Scanning System, orientation of discontinuity, roughness of joint surface, failure shape and volume were successively achieved. in the case of tunnel face, through reverse-engineering, monitoring of displacement was possible.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.83-92
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• 2017

This paper deals with numerical analysis of behavior of curved mechanically stabilized earth(MSE) walls with geosynthetics reinforcement. Unlike typical concrete retaining walls, MSE wall enables securing stability of higher walls without being constrained by backfill height and is currently and widely used to create spaces for industrial and residential complexes. The design of MSE walls is carried out by checking external stability, similarly to the external checks of conventional retaining wall. In addition, internal stability check is mandatory. Typical stability check based on numerical analysis is done assuming 2-dimensional condition (plane strain condition). However, according to the former studies of 3-dimensional MSE wall, the most weakest part of a curved geosynthetic MSE wall is reported as the convex location, which is also identified from the studies of the laboratory model tests and field monitoring. In order to understand the behaviour of the convex location of the MSE wall, 2-dimensional analysis clearly reveals its limitation. Furthermore, laboratory model tests and field monitoring also have restriction in recognizing their behaviour and failure mechanism. In this study, 3-dimensional numerical analysis was performed to figure out the behaviour of the curved part of the geosynthetic reinforced wall, and the results of the straight-line and curved part in the numerical analysis were compared and analysed. In addition, the behaviour characteristics at each condition were compared by considering the overburden load and relative density of backfill.

• Environmental and Resource Economics Review
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• v.26 no.3
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• pp.399-416
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• 2017

This study examines the problem of efficient scheduling of waste collection in isolated regions like islands when the waste accumulated amount surpasses the standard ceiling by effectively tracking the accumulating trends based on the optimum checking model of Keller (1974). To grasp whether the waste accumulated amount in isolated regions exceeds the standard ceiling, the relevant authorities can tightly check during a set period, but this entails higher monitoring costs. On the other hand, if the accumulated waste over the ceiling is not immediately checked and collected, and continues for a set period of time, innovative efforts for waste management may be highly demanded. As such, the tradeoffs are considered to draw the optimal checking schedule. This study shows that the authorities get to check less frequently the waste accumulation trends if the monitoring costs increase or when the failure rate of waste management systems drops. On the other hand, they get to check more frequently if the accumulated waste amount in isolated regions exceeds the standard ceiling and welfare loss grows as a result. It also shows that frequent checking is the optimal choice if the social marginal benefits enjoyed from innovative efforts made to keep accumulated waste below the standard ceiling, are not significant.

• Journal of the Korean Geotechnical Society
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• v.37 no.7
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• pp.13-23
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• 2021

If roads, bridges, buildings, etc. are built on the ground with soft clay or organic soil, there may be a lot of problems in geotechnical engineering such as settlement and stability due to the large settlement and lack of bearing capacity. In extreme cases, it may appear due to shear failure or collapse of the constructed structure, so a ground improvement method is indispensable to increase the strength of the ground and to suppress settlement. In this study, the settlement according to each groundwater level condition was analyzed using the measurement results for the groundwater level conditions, one of the important factors in predicting the settlement in dredged and reclaimed ground, and the groundwater level conditions applied to the settlement analysis were proposed by comparing it with settlement generated 5 years after construction. As a result of the analysis, it is judged that it is reasonable to apply the measured groundwater level during construction and the low water ordinary neap tide (L.W.O.N.T) during load application for the groundwater level in the settlement analysis. In addition, in the case of the dredged and reclaimed ground, it is estimated that the water pressure acting on the clay layer is nonlinear, as the result of the observations of the head of water at the observation points above and below the in-situ clay layer were different.