• The Journal of Engineering Geology
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• v.28 no.4
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• pp.553-563
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• 2018

The recent increase of ground subsidence in Korea requires the development of technology for predicting the possibility of ground subsidence. Eighteen parameters affecting the ground subsidence for pre-excavation are classified into 6 categories considering ground types, groundwater, and external factors. Eighteen parameters consists of a table which gives ground subsidence risk ratings for pre-excavation(GSRp). Certain scores are given to these parameters after they are divided into several classes considering the importance and the credibility of parameters and the engineering judgements of the authors. Because of the difference of ground subsidence factors depending on the ground and field conditions, weighting factors for the individual factor and for the each category are multiplied. Weighting factors are calculated from citation frequencies of influencing factors. Ground subsidence risk ratings for pre-excavation can be quantified by considering the individual score of each parameter and weighting factors for the individual factor and for the each category. The suggested GSRp tables obtained from this study are expected to be used by engineers for the estimation of ground subsidence risk ratings for pre-excavation sites.

• The Journal of Engineering Geology
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• v.27 no.2
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• pp.153-164
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• 2017

The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.

• Journal of the Korean GEO-environmental Society
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• v.25 no.1
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• pp.5-11
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• 2024

Ground subsidence mainly occurs in urban areas with high population density, so it is necessary to clearly identify the cause of occurrence and prepare in advance. The main cause of ground subsidence is reported to be the creation of cavities in the ground due to damage to underground pipes, but the property information and influencing factors of underground pipes to predict and prepare for ground subsidence are not properly established. Therefore, in this study, factors showing a significant correlation with the occurrence of ground subsidence were selected among the underground facility property information and a regression equation was proposed through logistic regression analysis. For this purpose, data on underground structures and ground subsidence history information in the target area were collected, and the target area was divided into girds of 100m x 100m in size using QGIS. The underground facility attribute information and ground subsidence history information contained within the gird were extracted. Then, preprocessing was performed to construct a dataset and correlation analysis was performed. As a result, factors excluding the year of sewer pipes and communication pipes and the average depth of communication pipes, heat pipes, and gas pipes were found to have a significant correlation with ground subsidence. In addition, a regression equation for whether ground subsidence occurred in the target area is proposed through logistic regression analysis.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.135-148
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• 2021

Ground subsidence risk ratings obtained from the site investigation during pre-excavation stages could be changed depending on the parameters revealed during construction activities. A method of correcting the pre-excavation ground subsidence risk ratings based on the site conditions observed in the field is suggested in this study. The elevation of groundwater table during the excavation may be different from the predicted value depending on the application of waterproofing methods and construction conditions. The drastic drawdown of groundwater table during the excavation could cause ground subsidence due to soil volume decrease related to consolidation or compression of the ground, whereas the rising of groundwater table caused by the intense rainfall may result in a high potential for ground subsidence due to heaving or boiling of the excavation bottom. Excessive displacements of retaining walls or ground settlements may cause ground subsidence, which also results in a high risk of ground subsidence caused by the destruction of buried pipelines. Reevaluation of ground subsidence risk ratings is suggested considering the fluctuation of groundwater table, condition of groundwater leakage, measured ground displacements, and soil types. Finally, the ground subsidence risk rating system is improved for better evaluation by using 12 factors in 5 categories.

• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.43-46
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• 2017

Recently, the development of underground space is being actively carried out in the urban area by saturation, and the excavation works are mainly carried out by various excavation methods by the structures adjacent to the ground and underground excavation. During such excavation work, ground subsidence accidents are occurring due to inattention construction, lack of construction technology, and leakage of ground water. For the prevention of ground subsidence we studied the method of risk influence factors by soil investigation. Analysis of 75 sites soil investigation by U.S.C.S (Unified Soil Classification System), construction method, depth of excavation and we studied the risk influence factors with ground subsidence.

• Tunnel and Underground Space
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• v.30 no.2
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• pp.149-163
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• 2020

This paper presents a logistic regression and GIS based urban ground sink susceptibility assessment using underground facility information considering soil particle loss. In the underground environment, the particle loss due to water flow or groundwater level change leads to the occurrence and expansion of cavities, which directly affect the ground sink. Four different contributory factors were selected according to the two underground facility domains (water pipeline area, sewer pipeline area) and subway line area. The logistic regression method was used to analyze the correlation and to derive the regression equation between the ground sink inventory and the contributory factors. Based on these results, three ground sink susceptibility maps were generated. The results obtained from this study are expected to provide basic data on the area susceptible to ground sink and needed to safety monitoring.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.27-36
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• 2018

The collapse behavior of ground subsidence caused by continuous loss of particles depends on the saturated condition and density of the ground. In this study, types of ground subsidence were classified based on the saturated condition and each type was performed on the different relative density to analyze the influence factors on the collapse behavior by distinct element method. According to analysis results, the relatively small amount of settlement occurred on the dense ground and a cavity was created under dense-unsaturated ground. In contrast, loose ground showed the large amount of settlement and collapsed immediately without cavity formation even if the unsaturated ground was simulated. The results demonstrated that because the relative density has influence on the mechanical interlocking and saturated condition has influence on the inter-particle force, these are important factors to change the collapse behavior.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.235-253
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• 2018

Groundwater flow induced by cracks in a buried pipe causes ground loss in the vicinity of it which can lead to underground cavities and sinkhole problems. In this study, the ground collapse mechanism and the failure mode based on an aperture in the pipe located in cohesionless ground were investigated through a series of physical model studies. As the influence parameters, size of the crack, flow velocity in the pipe, groundwater level, ground cover depth and ground composition were adopted in order to examine how each of the parameters affected the behavior of the ground collapse. Influence of every experimental condition was evaluated by the final shape of ground failure (failure mode) and the amount of ground loss. According to the results, the failure mode appeared to be a 'Y' shape which featured a discontinuous change of the angle of erosion when a groundwater level was equal to the height of the ground depth. While in the case of a water table getting higher than the level of ground cover depth, the shape of the failure mode turned to be a 'V' shape that had a constant erosion angle. As the height of the ground depth increased, it was revealed that a mechanism where a vertically collapsed area which consisted of a width proportional to the ground height and a constant length occurred was repeated.

• Magazine of the Korean Society of Agricultural Engineers
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• v.61 no.1
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• pp.65-71
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• 2019

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.35-43
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• 2017

It is a method of suppressing back ground subsidence by re-injecting groundwater back to the target ground and recovering the underground water level. In order to analyze the subsidence of the back ground due to maintaining the underground water level, indoor model experiments were conducted. Through this study, the factors influencing on the groundwater and the tendency of subsidence back ground by experiments were analyzed and the effect of ground subsidence by reinfusion of groundwater was also investigated. As a result of the subsidence analysis with considering only the influence of the underground water level, the settlement of the ground occurs as the underground water level at the time of ground excavation goes down. The closer to the back of the retaining wall, the maximum settlement occurred. Moreover, it was analyzed that the influence distance where subsidence occurs from retaining wall to the point of about 1.8 H on the basis of the ground collapse. The most effective location of water reinjection is the closet location to the back of braced-cut wall for reducing the groundwater down and also minimizing the ground settlement.