• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.3
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• pp.279-289
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• 2003

In karst formation area, the tunnel support system is an important factor for the tunnel safety during operation. It is also not easy to determine the tunnel supporting system in the design stage. Therefore, it is necessary to standardize the tunnel supporting system in uncertain ground condition. This paper presents the standardization of the tunnel supporting systems to be adopt in karst formation. For the tunnel planned in the project area, karst features and the expected scenarios in the tunnel area were developed based on the results of the geological and geotechnical assessment. In order to provide specific supporting system and construction details for a wide range of possible karst features, the generalized typical support systems are developed according to the classification of karst features. In addition, the initial support systems and construction sequence for each karst feature are also presented in this paper.

• The Journal of Engineering Geology
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• v.18 no.1
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• pp.7-16
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• 2008

Limestone area have mostly certain geological defects such as the internal cavities due to melting and fractured zone by external pressures. Especially, in case of constructing grand bridge, the treatment of the limestone cavities area having the geological defects is inevitable. In order to reduce foundation settlement and to reinforce the ground in the limestone cavities area, high pressure jet grouting has been carried out as a countermeasure method. Despite the fact that high pressure jet grouting method has already adopted at a lot of limestone cavities area, but the amount of research and technical data on the high pressure jet grouting have not been accumulated properly so for. Therefore this paper intends to investigate the strength characteristics and deformation characteristics for reinforced limestone cavities area by high pressure jet grouting method. In addition, load carrying capacity obtained by static pile load test with load transfer measuring system is analyzed.

• Journal of the Korean GEO-environmental Society
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• v.6 no.1
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• pp.63-72
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• 2005

From the geological and engineering point of view, the limestone is so rigid that it is able to act as a bedrock but if there are some unstable elements which are solubility cavity and cracking zone in the ground, the settlement and bearing capacity of a structure will be required to long-term stability investigations and countermeasures about those problems. When comparing the allowable bearing capacity, the results of Bell's method and the Bowles' method are similar but the results of Hoek-Brown's method are very larger than the others. For weathered limestone, stability is changed by size and depth of the cavity of limestone, but soft and hard rock are stable regardless of size and depth of the cavity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.113-121
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• 2002

This study is focused on establishing influence zone caused by tunnelling in limestone site. Therefore, the numerical analysis using the FLAC2D was performed considering various locations and magnitudes of cavities. To reduce the stress concentration, the shape of cavities was designed to ellipse. This parametric study reveals that the cavities located at crown part and edge part of tunnel greatly have influenced on stability of tunnel. The effect of distance between tunnel and cavity which is larger than 1-0D (Tunnel diameter) dose not directly related to stability of tunnel, but the nearer a cavity location was, the larger displacement and stress of reinforcement occured within 0.25D.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2007.03a
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• pp.64-80
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• 2007

This paper presents a case study on the excavation of a long tunnel(16.2km) named as "Sol-An tunnel", which connects between Mt. Dongbaek station and Dokye station in the Young-dong Railroad. This site is located in a complex geological region with faults, cavities and coal measures as sedimentary rocks area. It occurred geotechnical problems unexpectedly by running water when tunnelling in limestone area within those geological structures. This tunnel caused surface settlements through the decrease of ground water level and soil washed-out affecting by cavities and faults within limestone formation. This paper presents a analysis of source through a close investigation and measures. And also, does preventive measures about returns of settlements reflected by properties of limestones.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.10a
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• pp.81-85
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• 2006

• Journal of the Korean GEO-environmental Society
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• v.14 no.12
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• pp.43-52
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• 2013

Limestone typically forms large caverns such as reticular caverns or limestone caves, and also forms sinkhole and doline. These caverns cause different settlement when constructing roads, dams, etc. because the foundation cannot sustain the upper structures. So it is necessary to reinforce foundation such as cavern filling method, etc. In this study, ground reinforcement for structure foundation was carried out using CGS method in limestone cavity area and evaluation of reinforcement effect from engineering viewpoint was conducted through the field test. Among others, boring test was carried out to identify the ground structure and engineering characteristics. After CGS reinforcement, boring test was conducted for supplementary verification, and with reinforcement core taken during boring test, rock test was carried out to identify the physical properties of reinforcement material. After applying CGS method, rock test of the typical specimen, among reinforcement cores, taken from boring test was carried out and physical properties of the reinforcement was identified. As a result of compressive test of core sample, material inside the cavity was filled properly, indicating compressive strength of 12.2~19.2(MPa) which was evaluated acceptable. Thus the limestone cavity proved to have been reinforced successfully.

• Journal of the Speleological Society of Korea
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• no.48
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• pp.9-16
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• 1996

석회동굴은 유구한 지구 표면 지층의 역사를 되새겨 주는 석회암 층에서 형성되는 지하동굴이다. 바다 속에서 퇴적되어 형성된 석회암 층이 융기 작용으로 지표면에 상승되어 이른 바 석회암 지표 층을 이루고 있는 곳에서는 빗물에 의한 화학작용으로 땅 표면에서 카르스트 윤회과정의 갖가지 지형지물이 발달되는데, 이 때에 지하에 스며든 지하수의 물리 작용으로 곧 지하수류가 흘러 지나간 공동이 생기게 되고, 나아가서는 낙반 및 확장 등으로 지하동굴이 확장되는데, 2차적인 지하수 침투작용으로 석회질 용해수에 의한 2차 생성물이 형성되어 이른 바 화려한 석회동굴이 이루어진다. 그 석회암의 화학 성분 여하에 따라, 그리고 지하수의 지하 투수량에 따라 석회동굴의 양상은 달리 나타나게 된다.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.537-547
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• 2011

Electrical resistivity tomography surveys using boreholes were applied to reveal the cause of a catastrophic land subsidence accompanied by the excessive groundwater withdrawal in urban karst area and to map the connectivity of disseminated cavities over the study area. In order to understand the hydrogeological characteristics, resistivity using exsitu core samples, groundwater level for five boreholes, and hydraulic conductivity using slug test were measured. The hydraulic conductivity variation ranging from 0.8 to $9.3{\times}10^{-4}\;cm/s$ for five boreholes and a gentle slope of groundwater level indicated that there is no significant characteristics of hydraulic heterogeneity. Core samples of the lime-silicated rock were classified as three groups including cracked, weathered, and fresh and measured the resistivity values ranged from 103 to 161, 218 to 277, and 597 to 662 ohm-m, respectively. Drilling results that showed the cavity filled with clay materials and tomogram for this region indicated resistivity value lower than 50 ohm-m. From the inverted resistivity results for each section with five boreholes, cavity and fractured layer were distributed along the depth between 10 and 20 m overall area and cavities ranging from 4 to 6 m filled with clay materials.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.51-57
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• 2011

Irregular distributions of limestone cavity in Gang-Won province area may cause unexpected accidents from reduced serviceability or failure of structure. It is requested that an appropriate ground reinforcement method should be used to improve bearing capacity of structure, and the method should also be satisfied with environmental requirements. Among several methods used for foundation constructions in cavity area, Rod Jet Pile(RJP) method has been widely used. While the RJP method was used to improve bearing capacity for the railway bridge foundations, water pollutions of drinking water as well as fishery located adjacent to this project area were occurred. The main reason of the water pollution was cement runoff used in cement mortar during injecting material in RJP method. Laboratory tests were performed to prevent water pollution. The compaction mortar method using low movable material was selected for this project. The quality of water at a fishery adjacent to the site and the compressive strength of cores taken from the construction site were measured. Test results show that the water pollutions was minimized, and the average compressive strength of foundation material was over 5 MPa. As a result of this study, compaction mortar method can be used to ensure the bearing capacity of foundation and to prevent environment pollutions.