• Journal of Environmental Impact Assessment
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• v.20 no.4
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• pp.557-564
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• 2011

This study was conducted to investigate the sudden rise of fine particle concentration after the passage of typhoon USAGI and NARI in Busan. Nocturnal inversion layer was formed at atmospheric boundary layer and wind direction changed from southerly wind to northeasterly wind after USAGI passed through Busan. Fine particle concentration in Busan rapidly increased by subsidence of air pollutants released from sources and dust transported from in the vicinity of industrial regions. Wind direction changed from northeasterly wind to southeasterly wind, wind velocity increased and lower atmosphere became extremely unstable after NARI passed through Busan. $PM_{10}$ concentration of Busan increased sharply because of surface dust dispersed by strong wind. Fine particle concentration generally decreases by precipitation and wind after typhoon passes through. However, the concentration can also go up not only by subsidence and transportation in nocturnal inversion layer but also by surface dust which temporarily occurs by strong wind.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.5
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• pp.375-384
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• 2013

Most of regions within the city of Mokpo, located on the southwest coast of the Korean Peninsula, are subjected to significant subsidence because about 70% of the city is land reclaimed from the sea (Kim et al., 2005). In this study, we aimed to estimate the rate of subsidence over Mokpo by using PALSAR L-band dataset from 2006 to 2010. Time series analysis was performed as well using GPS surveying data from 2010 to 2012. Results from these two independent datasets are then compared and analyzed over the common period of time. GPS data processing provides the results of seasonal variation on the surface, that is, via repeatedly rising and falling in association with the periodic cycle. Therefore, a time series analysis was performed to calculate the rate of ground subsidence. The deformation rates calculated for the same point are 3.89cm/yr and 2.65cm/yr from the GPS data and SAR data, respectively. SAR and GPS data processing results show a very similar pattern in terms of magnitude of annual subsidence. Thus, if the two datasets are integrated together, new modeling on ground subsidence is feasible. Lastly, subsidence was detected in a landfill area in the city of Mokpo, which has been continuously occurring through 2012.

• Journal of the Korean GEO-environmental Society
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• v.19 no.8
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• pp.11-17
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• 2018

Recently, road subsidence has been increasing in urban areas, threatening the safety of citizens. In the lower part of the road, various road facilities such as water supply and drainage pipelines and telecommunication facilities are buried, and the deterioration of the facilities causes the road subsidence. Especially, in the case of old sewer which are attracting attention as a main cause of ground subsidence, the risk of subsidence is calculated indirectly through CCTV exploration. Currently, we are finding cavity through GPR exploration. However, it is difficult to find the sewer back cavity because it is explored from the surface of the road. Thus, the nondestructive cavity exploration techniques was investigated in this study and we confirmed the applicability through experiments on the test-bed. In this study a new quantitative method is proposed to detect the cavity around sewer.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.321-329
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• 2003

The change of strain-dependent hydraulic conductivity around mined panels due to subsidence is examined where normal and shear strains, modulus reduction ratio and joint spacing are major factors controlling the changes of hydraulic conductivity. Modulus reduction ratio and joint spacing are defined through RMR and RQD, respectively. Utilizing these two empirical parameters, changes of hydraulic conductivity values of a full gamut of rock mass conditions are determined. The change of hydraulic conductivity is not apparent in the near surface area and more significant change takes place in the area around mined panels. A zone of strong influence from the subsidence extends to a height of approximately 20m above mined panels. The shear strain does also play the role of increasing a hydraulic conductivity around mined panels. As RMR of rock mass decreases, a hydraulic conductivity is found to be increased and this means that subsidence in a poor rock with low RMR has a great effect on a hydraulic conductivity field.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.174-181
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• 2001

The cavities created by underground mining, if remained unfilled, can cause ground settlement and surface subsidence as a result of relaxation and breakdown of the carven roof. Construction of structures above the underground mine cavity will have serious problems concerning both structural stability and safely even if the cavity is back-filled. This study was conducted to confirm the location and condition of the cavern as well as the state of the back-fill in A mine area using core logging and borehole camera. The bearing capacity and other mechanical properties of the ground were also measured by the standard penetration test(SPT). Obtained data were used to assess the stability of the ground and the structures to be built by numerical analysis using FLAC. The site investigation results showed that the mine cavities were filled with materials such as boulder and silty sand(SM by unified classification). Result of the numerical analyses indicated that constructing building structures on the over-lying ground above the filled cavities is secure against the potential problems such as surface subsidence and ground settlement.

• Journal of the Korean earth science society
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• v.34 no.3
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• pp.195-208
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• 2013

We employed electrical resistivity and optical borehole imaging methods to identify underground cavities and determine ground subsidence rate at the study area affected by land subsidence due to abandoned underground mines. At the study site 1, the anomalous zones of low resistivity ranging between 100 ohm-meter and 150 ohm-meter were observed and confirmed as an abandoned underground mine by subsequent borehole drilling and optical borehole imaging. Although the electrical resistivity survey was unavailable due to the paved surface of the study site 2, we were able to locate another abandoned underground mine with the collapsed mine shaft based on the distribution of the ore veins and confirmed it with borehole drilling. In addition, we measured vertical displacements of underground features indicating underground subsidence by conducting optical borehole imaging 6 times over a period of 43 days at the study site 2. The displacement magnitude at the deep segment caused by subsidence appeared to be 3 times larger than those at the shallow segment. Similarly, the displacement duration at the deep segment was 4 times longer than those at the shallow segment. Therefore, the combination of electrical resistivity and optical borehole imaging methods can be effectively applicable to detect and monitor ground subsidence caused by underground cavities.

• International conference on construction engineering and project management
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• 2024.07a
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• pp.102-111
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• 2024

Roadbed stability is paramount in urban areas as it directly affects public safety and city operations. South Korea's major metropolis has experienced 1127 cases of ground subsidence since 2014, affecting subways, roads, railways, and construction sites. Notably, about 40% of these incidents coincide with heavy summer rainfall, while 60% resulted from utility damage, improper backfill, and groundwater fluctuations. Subsequently, roadbed instability leads to a range of cascading hazards, including sinkholes and road failures, endangering public safety and the economy. Therefore, continuous monitoring of roadbed stability and implementing proactive measures are essential for a resilient transportation infrastructure. However, terrestrial in-situ observations like GPS provide accurate surface's displacement with high temporal accuracy but limited spatial resolution. To address this issue, we used the InSAR permanent scatterer (PSInSAR) technique to process 35 Sentinel-1 SLC datasets acquired between 2017 and 2022 to monitor and prevent cascading hazards in Daejeon City, South Korea. The results revealed an average subsidence rate of -0.88mm/year with a maximum of -7.73 mm/year. Notably, the southern part of the city exhibited significant roadbed instability, with an average and maximum cumulative subsidence of -5.13 mm and -44.95 mm, respectively. The deformation data was then integrated with road geometry to develop a vulnerability map of the city, highlighting the pronounced roadbed deformation in the southern region. Time-series subsidence variations correlated with groundwater fluctuations data from 2017 to 2022, showing a decline in groundwater levels from 4.63m to 9.9m in the southern region. Furthermore, a comparison between subsidence rates and effective shear wave velocity (V_s³⁰) revealed that most subsidence events were associated with V_s³⁰ values below 420 m/sec, indicating a clear lithological influence on the spatial distribution of roadbed instability. Thus, the integrated geotechnical and hydrogeological data with PSInSAR monitoring can better understand the processes responsible for roadbed instability in areas with small-scale variations.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.689-699
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• 2023

Assessing ground stability is critical to the construction of underground transportation infrastructure. Surface displacement is a key indicator of ground stability, and can be measured using interferometric synthetic aperture radar (InSAR). This study measured time-series surface displacement using permanent scatterer InSAR applied to Sentinel-1 SAR images acquired from January 2017 to June 2023 for the area around a deep underground expressway under construction to connect Mandeok-dong and Centum City in Busan, South Korea. Regions of seasonal subsidence and uplift were identified, as were regions with severe subsidence after summer 2022. To evaluate stability of the ground in the construction area, the mean displacement velocity, final surface displacement, cumulative surface displacement, and difference between minimum and maximum surface displacement were analyzed. Considering the time-series surface displacement characteristics of the study area, the difference between minimum and maximum surface displacement since June 2022 was found to be the most suitable parameter for evaluating ground stability. The results identified highly unstable ground in the construction area as being to the north of the mid-lower reaches of the Oncheon-cheon River and to the west of the Suyeong River at the point where both rivers meet, with the difference between minimum and maximum surface displacement of 40~60 mm.

• Economic and Environmental Geology
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• v.45 no.5
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• pp.503-512
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• 2012

We performed DInSAR (Differential Interferometric SAR) and SBAS (Small BAseline Subset) analysis using spaceborne SAR (Synthetic Aperture Radar) in order to detect a surface subsidence in Taebaek area, Kangwon, which are suitable to the monitoring of broad and inaccessible areas. During the period from October 2006 to June 2010, we acquired twenty-three ALOS PALSAR data sets (path/frame=425/730) for this study. The ninety-six differential interferograms with a perpendicular baseline less than 1100 m were constructed by ROI_PAC, then the mean velocity map of surface displacement was derived from SBAS analysis. As a result, it was confirmed that the ground displacement occurred about 4 cm/yr at Seokgong-Jangseong and Kyungdong mines and 2 cm/yr at Saehan-Eoryong-Jungdong and Hwangji mines in Taebaek area, Kangwon. It seems that the subsidence in study area is closely related to mining activities because the most of subsiding areas are well matched with mining areas. The subsidence at Kyungdong mine shows continuous and fast velocity in about $2{\times}2$ km area. Therefore the further analysis and the effort to prevent disaster are required in this area.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.168-171
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• 2001

It is a common practice to extract water from the ground for domestic, agricultural or industrial uses or to lower the groundwater level for construction work. An accurate prediction of ground settlement Is sometimes crucial when groundwater is pumped. This case study have shown that drawdown of the groundwater table may cause ground subsidence. Many settlement gauges was installed in the vicinity of a pumped well to measure the surface settlement. The relationships between the level of groundwater drop and surface settlement is investigated In this research.