• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.11-21
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• 2017

Ground subsidence mainly occurs due to the soil wash-away caused by cracked sewer pipes. It is necessary to understand the behavior surrounding soils with the formation of cavity and relaxation zone to set up counterplan. In this paper, a series of laboratory model tests and numerical analyses (Discrete Element Method) were performed to investigate the ground subsidence mechanism due to sewer pipe damage. For model tests, aluminum rod and trap door were used to simulate the behavior of model ground. Test results were compared with the numerical analyses conducted under the same boundary conditions with model tests. From this study, it was investigated the shape and size of cavity and relaxation zone due to the soil wash-away and a void ratio distribution of surrounding soils with relaxation properties.

• The Journal of Engineering Geology
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• v.25 no.4
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• pp.511-524
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• 2015

Groundwater causing subsidence in limestone mines is uncommon, and thus relatively poorly investigated. This case study investigated the cause and possibility of future subsidence through an evaluation of ground stability at the Samsung limestone mine, Chungcheongbuk-do. The ground near the mine area was evaluated as unstable due to rainfall permeation, and subsidence in the unmined area resulted from groundwater level drawdown. Future subsidence might occur through the diffusion of subsidence resulting from the small thickness of the mined rock roof, fracture rock joints, and poor ground conditions around the mine. In addition, the risk of additional subsidence by limestone sinkage in corrosion cavities, groundwater level drawdown due to artificial pumping, and rainfall permeation in the limestone zone necessitates reinforcements and other preventative measures.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.67-74
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• 2017

In order to prevent the ground subsidence accidents caused by the occurrence of underground cavity, it is necessary to evaluate the mechanical characteristics in the relaxation zone of the underground cavity. Also, the relaxation zone including underground cavity be appropriately reinforced. This paper described analysis results based on finite element method that was conducted to analyze the mechanism for occurrence of the relaxation zone around the underground cavity. The finite element analysis applied in forced displacement was carried out to simulate the underground cavity and relaxation zone, and then there were compared with previous research results. The analysis results showed that the void distribution of soil around the underground cavity has figured out. As a result, the area of the relaxation zone could be quantitatively presented by reduction characteristics of the shear stress.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.8 no.3
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• pp.1-11
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• 2012

Mongolia has three(3) geothermal zones and eight(8) hydrogeothermal systems/regions that are, fold-fault platform/uplift zone, concave-largest subsidence zone, and mixed intermediate-transitional zone. Average temperature, heat flow, and geothermal gradient of hot springs in Arhangai located to fold-fault platform/uplift zone are $55.8^{\circ}C$, 60~110 mW/m2 and $35{\sim}50^{\circ}C/km$ respectively and those of Khentii situated in same zone are $80.5^{\circ}C$, 40~50 mW/m2, and $35{\sim}50^{\circ}C/km$ separately. Temperature of hydrothermal water at depth of 3,000 m is expected to be about $173{\sim}213^{\circ}C$ based on average geothermal gradient of $35{\sim}50^{\circ}C/km$. Among eight systems, Arhangai and Khentii located in A type hydrothermal system, Khovsgol in B type, Mongol Altai plateau in C type, and Over Arhangai in D type are the most feasible areas to develop geothermal power generation by Enhanced Geothermal System (EGS). Potential electric power generation by EGS is estimated about 2,760 kW at Tsenher, 1,752 kW at Tsagaan Sum, 2,928 kW at Khujir, 2,190 kW at Baga Shargaljuut, and 7,125 kW at Shargaljuut.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.545-552
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• 2017

Ground subsidence can result in the formation of sinkholes, potholes, settlement of structures, and road subsidence. Road subsidence is described as the sudden collapse of the road surface into subsurface cavities caused by the loss of bearing capacity in the ground, such as the dissolution of limestone by fluid flow in the surface causing the formation of voids leading to subsidence at the surface. Road subsidence occurs about 665 times annually, and this incidence has been increasing until 2013. Damaged underground facilities, management negligence, and lowering of the ground water table have been the causes of road subsidence in Seoul. Seoul metropolitan government announced special management counter plans to relieve the anxieties and make the roads safe for passing. Construction sites, such as excavation works, need to be managed properly because they have strong potential to induce road subsidence. The aim of this study was to identify the main causes of road subsidence and suggest management plans. First, life cycle cost analysis revealed the daytime construction to be more appropriate than nighttime. In addition, by analyzing the limitations of using sand as a backfill material, it is proposed to use a flowable backfill material instead of sand. Finally, to reduce the blind spots, which is a problem in surveying the road pavement conditions of local governments, the road to be managed is divided into several zones, and a specialized agency is selected for each zone and a method of surveying the blind spots through collaboration is suggested.

• 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.25 no.4
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• pp.332-340
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• 2015

Ground subsidence occurring in mine area can cause an enormous damage of loss of lives and properties, and a systematic survey should be conducted a series of field investigation and ground stability analysis in subsidence area. This study describes the results from field investigation and ground stability analysis in a limestone mine located in Cheongwon-gun, Chungcheongbuk-do, Korea. Rock mechanical measurements and electrical resistivity surveys are applied to obtain the characteristics of in-situ rock masses and the distribution patterns of subsurface weak zone, and their results are extrapolated in numerical analysis. From the field investigation and stability analysis, it is concluded that the subsidence occurrence in this limestone mine is caused mainly by subsurface limestone cavities.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.28-34
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• 2003

A problem of ground subsidence has been a focus of our research over the past 3 years. The purpose of this study is to investigate the disturbed stratigraphic structure by mining and to separate the possible ground subsidence area using shallow seismic reflection survey and processing. To overcome the problems such as the distortion and attenuation of seismic signal caused by ground disturbance and to acquire the high frequency data, an array with short spacing (0.3m) for both the shot and receivers, yielding near-offset (<30m) and CMP spacing of 0.15m was implemented. Data were acquired along the survey line with length of about 43m by fixed receiver array. By considering statics caused by the ground disturbance and offset distribution of data, careful processing steps such as muting and residual statics correction were applied for successful shallow reflection imaging. By correlating the ground subsidence data and stack section, possible subsidence zone could be interpreted quantitatively.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.368-372
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• 2008

This study evaluates the usefulness and capability of surface electrical resistivity technique for identifying the weak zones or subsurface cavities in karst area with limestone formation. Weak zones or cavities near surface can be potentially dangerous and several problems are associated with collapse of roads or buildings accompanied by subsidence phenomena. In this paper, both two and three dimensional resistivity investigation were conducted to investigate subsidence along a road in Yongweol-ri, Muan-gun, South Korea. The results of the resistivity survey using dipole-dipole array provide a clear view of the weathered regolith, the distribution of weak zones or cavities and bedrock. Several low resistivity areas were identified and subsequent drilling led to the discovery of several weak zone or clay-filled underground cavities. The drilling results show excellent correlation with the resistivity images. It is illustrated, the ability of electrical technique to produce high resolution images of subsurface, which are useful for subsidence assessment. Also the results of this study have demonstrated that two and three dimensional electrical resistivity surveys are useful for delineating the subsidence area. Based on resistivity imaging, the map of hazardous zone has been developed.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.165-170
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• 2020

The groundwater during tunnel excavation not only affects the stability of the tunnel and constructability but also causes the subsidence of the upper ground due to the lowering of groundwater. Generally, the cutoff grouting is applied as a countermeasure to reduce the groundwater inflow during tunnel excavation, and the cutoff grouting is often applied in the range of plastic zone around the tunnel. However, grouting in the plastic zone is only appropriate for ground reinforcement purposes, and guidelines for the application range of cutoff grouting and the targeted permeability coefficient of the grouting zone are required. In this study, the relationship between groundwater inflow into tunnel and application range of cutoff grouting and permeability coefficient is proposed and compared with numerical analysis results. It was found that grouting with tunnel radius thickness is appropriate to reduce the groundwater inflows effectively. More than 90% reduction in groundwater inflow can be achieved when the annular area of the tunnel radius thickness is grouted with a permeability reduction ratio of 1/50~1/200.