• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.376-383
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• 2005

In this study, we conducted geophysical investigations for the organization of integrated geophysical methods to detect underground cavities of ground subsidence area at the field test site, located at Yongweol-ri, Muan-gun. We examined the applicability of geophysical methods such as electrical resistivity, electromagnetic, and microgravity to cavity detection with the aid of borehole survey results. Underground cavities are widely present within the limestone bedrock overlain by the alluvial deposits in the area of the test site where the ground subsidences have occurred in the past. The limestone cavities are mostly filled with groundwater and clays in the test site. Thus, cavities have low electrical resistivity and density compared to the surrounding host bedrock. The results of the study have shown that the zones of low resistivity and density correspond to the zones of the cavities identified in the boreholes at the site, and that the geophysical methods used are very effective to detect underground cavities. Furthermore, we could map the distribution of cavities more precisely with the test results incorporated from the various geophysical methods. It is also important to notice that the microgravity method is a very promising tool since it has rarely used for the cavity detection in korea. Beyond the investigation of underground cavities, the geophysical methods are required to provide useful information for the reinforcement design for the ground subsidence areas. It is, therefore, necessary to develop integrated geophysical technique incorporating different geophysical methods to precisely map underground cavities and image the subsurface of the ground subsidence areas.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.621-640
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• 2019

Quantitative stability assessment of underground cavities can be presented as a factor of safety based on the Shear Strength Reduction Method (SSRM). Also, SSRM is one of the stability evaluation methods commonly used in slope stability analysis. However, there is a lack of research that considers the relationship between the probability of occurrence of cavities in the ground and the potential failure surface of the slope at the same time. In this study, the effect of small underground cavities on the failure behavior of the slope was analyzed by using SSRM. Considering some of the glaciology studies, there is a case that suggests that there is a cavity effect inside the glacier in the condition that the glacier slides. In this study, the stability evaluation of underground cavities and slope stability analysis, where SSRM is used in geotechnical engineering field, was carried out considering simultaneous conditions. The slope stability analysis according to the shape and position change of underground cavities which are likely to occur in the lower part of a mountain road was analyzed by using SSRM in FLAC3D software and the influence of underground cavities on the slope factor of safety was confirmed. If there are underground cavities near slope potential failure surface, it will affect the calculation of a factor of safety. The results of this study are expected to be basic data on slope stability analysis with small underground cavities.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.147-152
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• 2006

In this study, we examined the applicability of three-dimensional electrical resistivity survey to detect underground cavities of ground subsidence area at the field test site, located at Yongweol-ri, Muan-gun in Korea. Underground cavities are widely present within the limesilicate bedrock overlain by the alluvial deposits in the area of the test site where the ground subsidences have occurred in the past. The limesilicate cavities are mostly filled with groundwater and clays in the test site. Thus, cavities have low electrical resistivity compared to the surrounding host bedrock. The results of the study have shown that the zones of low resistivity correspond to the zones of the cavities identified in the boreholes at the site, and that the three-dimensional electrical resistivity survey used are very effective to detect underground cavities.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.3
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• pp.241-250
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• 2007

During enlarging an existing tunnel under operation, unexpected excessive overbreaks and large cavities around the tunnel were found. It was an issue that they might influence the stability the new tunnel. The overbreaks and cavities are assumed that they were attributed to excessive blasting under the condition of insufficient ground investigation. To enlarge the existing tunnel safely, therefore, a remedy measure for the overbreaks and cavities is suggested.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.676-686
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• 2010

Damage Cases of variously type are reported that the ground subsidence is caused by the underground cavities at structure and construction works in lime stone or abandoned zone. A underground cavities by direct for zone having an effect on structure have been filled with cement agents. But this measure is urgently needed in materials and work methods, because ground water pollution at water down fillings and flow out, ground disturb at high participle, damage of farms and fishery. The research confirm application of filling method and filling materials of environmentally friendly and economical by Hi-FA new materials have both liquidity and viscosity from case reinforcement in APT site, Gunsan.

• Interaction and multiscale mechanics
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• v.4 no.1
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• pp.49-64
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• 2011

A methodology for jointed rock mass characterization starts with a research based on geological data and tests in order to define the geotechnical models used to support the decision about location, orientation and shape of cavities. Afterwards a more detailed characterization of the rock mass is performed allowing the update of the geomechanical parameters defined in the previous stage. The observed results can be also used to re-evaluate the geotechnical model using inverse methodologies. Cases of large underground structures modeling are presented. The first case concerns the modeling of cavities in volcanic formations. Then, an application to a large station from the Metro do Porto project developed in heterogeneous granite formations is also presented. Finally, the last case concerns the modeling of large cavities for a hydroelectric powerhouse complex. The finite element method and finite difference method software used is acquired from Rocscience and ITASCA, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.62-71
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• 2000

The abandoned mines causing settlement of the surface above and collapse of the cavities are the major influencing factor on the stability of the nearby underground structures. To prevent the harmful effect, the backfill methods are commonly applied to the cavities although the design criteria and the analysis method are not properly addressed in some cases. An approximate analytical method together with the numerical technique is considered in this study to simulate the gradual deterioration of the rock masses around the cavities and, therefore, the influential zone to the underground structures passing through the cavities. Also considered in this study is the backfill effect on the stability of the rock masses around the cavities. Specifically, the incomplete backfill effect is compared with that of the idealized backfill method by adopting elasto-plastic analysis involving a strain softening material law.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.787-807
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• 2018

When conducting the underground safety impact assessment under the special law in Korea, it is essential to investigate the occurrence of underground cavities. When underground cavities were discovered, the underground safety was assessed through numerical analysis. The previous study has suggested the stability evaluation based on the factor of safety by changing the 2D shape of the small underground cavity. In this study, the effects of small underground cavities considering 3D shapes were examined using a continuum analysis program and compared with the 2D results presented in previous study. If the 3-Dimensional shape of the underground cavity is found close to the sphere type, it would be reasonable to evaluate the factor of safety by the shear strength reduction method regardless of the size and position of the cavity. If a high-aspect ratio underground cavity with a depth of 2 m or more from the ground surface and an aspect ratio (a/b) of 2.0 or more is in the vertical direction, not only the factor of safety but the failure mode shape should be cautions in the stability evaluation using the shear strength reduction method. The results of this study are expected to be basic data on underground safety impact assessment.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.27-32
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• 2009

In this study, we examined the applicability of a 3D electrical resistivity technique for the probing of underground cavities at a field test site in a karst area in Yongweol-ri, Muan-gun, in the south-western part of the Korean peninsula. At the test site, where the ground has subsided in the past, underground cavities are commonly found in the limestone bedrock, which is overlain with alluvial deposits. The limestone cavities at the test site are mostly filled with groundwater and clay; hence, they show levels of electrical resistivity that are significantly lower than those of the surrounding host bedrock. The results of this study demonstrate that the zones of low resistivity correspond to the zones of the cavities identified in the boreholes at the site, and that our 3D electrical resistivity survey is a very effective tool for detecting and mapping underground cavities in a karst area.

• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.271-278
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• 2006

Investigations of underground cavities are required to provide useful information for the reinforcement design and monitoring of the ground subsidence areas. It is, therefore, necessary to develop integrated geophysical techniques incorporating different geophysical methods in order to accurately image and to map underground cavities in the ground subsidence areas. In this study, we conducted geophysical investigations for development of integrated geophysical techniques to detect underground cavities at the field test site in the ground subsidence area, located at Yongweol-ri, Muan-eup, Muan-gun, Jeollanam-do. We examined the applicability of geophysical methods such as electrical resistivity, electromagnetic, and microgravity to cavity detection with the aid of borehole survey results. The underground cavities are widely present within the limestone bedrock overlain by the alluvial deposits in the test site where the ground subsidences have occurred in the past. The limestone cavities are mostly filled with groundwater or clays saturated with water in the site. The cavities, thus, have low electrical resistivity and density compared to the surrounding host bedrock. The results of the study have shown that the zones of low resistivity and density correspond to the zones of the cavities identified in the boreholes at the site, and that the geophysical methods used are very effective to detect the underground cavities. Furthermore, we could map the distribution of cavities more precisely with the study results incorporated from the various geophysical methods. It is also important to notice that the microgravity method, which has rarely used in Korea, is a very promising tool to detect underground cavities.