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Abstract Discontinuities in rock mass behave as weak planes, and thus, understanding the behaviors of discontinuities is crucial to assess the stability of underground structures. It should be noted that shear characteristics of discontinuities are usually affected by the interaction among overburden depending on the depth, tectonic stresses, water pressure by ground water level and elevated temperature at depth. Thus, it is necessary to evaluate the variations of the frictional properties of rock discontinuities which can be suitable for the engineering problems. In this study, a series of shear tests were carried out on three types of rocks (Daejeon granite, Goheung diorite, and Linyi sandstone) which have a single saw-cut surface to investigate the shear characteristics of a rock discontinuity under various thermal -hydro-mechanical (T-H-M) conditions in a triaxial compression chamber. In addition to the tests on saw-cut specimens, the effect of surface roughness on shear characteristics was examined. Cement-mortar was used to reproduce identical rough discontinuities having JRC value of 2.05 and 11.63. The testing conditions were determined considering in situ THM conditions at the vicinity of an underground structure such as a disposal facility for radioactive waste, enhanced geothermal system, and oil reservoir. The experimental results were analyzed based on Coulomb's and Patton's failure criterion. It was observed that the shear characteristics of the discontinuity were sensitive to confining pressure and water pressure variations but not to temperature change below 80°C. XRD analysis and SEM observation were made to figure out the mechanism which causes the decrease of the friction angle. Clay minerals having layer lattice structure and soft powder grains may have reduced the friction angle. 1. Introduction Understanding the behaviors of rock discontinuities is of great importance to ensure the stability of an underground structure such as a disposal facility for radioactive waste, enhanced geothermal system, and oil/gas reservoir. In particular, the frictional behavior tends to change depending on the complex interaction among thermal, hydraulic and mechanical (T-H-M) characteristics and their coupled effects. Numerous studies including Lockner et al. (1982), Tembe et al. (2000) and Kim and Jeon (2016) have been performed to predict shear strength of discontinuities under T-H-M coupled conditions.
Park, Eui-Seob (Korea Institute of Geoscience and Mineral Resources) | Chung, So-Keul (Korea Institute of Geoscience and Mineral Resources) | Synn, Joong-Ho (Korea Institute of Geoscience and Mineral Resources) | Jeong, Woo-Cheol (SK Engineering & Construction) | Kim, Taek-Kon (SK Engineering & Construction) | Bae, Seong-Ho (_)
ABSTRACT The new system for storing LNG in rock caverns had been developed and verified through the design, construction and operation of a LNG pilot plant in Daejeon, Korea. Among the key technologies of the LNG storage system, drainage of groundwater and formation of an ice-ring are very important ones. These are strongly related to the complex mechanism between thermal and hydraulic characteristics of rock mass and groundwater. Through the previous researches, the core of ice-ring design is summarized as follows: propagation distance of 0&3176;C isotherms after the injection of LNG; groundwater penetration distance within 0°C isotherm; and change of joint aperture during/after ice-ring formation. It was confirmed that the propagation distance of 0°C isotherms after the injection of LNG affects the operation period of the drainage system, and can be predicted from the thermal properties of rock mass, and initial temperatures of LNG and surrounding rock mass. In this paper, the generalized Clapeyon equation defined in porous media was used to quantify the phenomena of cryo-suction during ice-ring formation. Also the effect of cryo-suction on joint apertures was investigated by thermo-hydraulic-mechanical coupled analysis with UDEC code. The numerical analyses were carried out with the following two models: simple three joint sets and LNG pilot cavern models. The effect of cryo-suction on aperture of rock joints was verified by the numerical analysis results of the pilot plant model. It was revealed that as temperature dropped, the joint aperture was gradually increased by shrinkage of rock mass as like the results of monitoring. And the cryo-suction occurs as groundwater is recovered and changed to ice for forming an ice-ring, and can affect the joint aperture instantly. Furthermore, the joint apertures around the cavern were decreased up to 0.01~0.035 mm, and the change of the joint aperture had little effect on the stability of the cavern.
Chung, So-Keul (Korea Institute of Geoscience and Mineral Resources) | Park, Eui-Seob (Korea Institute of Geoscience and Mineral Resources) | Synn, Joong-Ho (Korea Institute of Geoscience and Mineral Resources) | Jeong, Woo-Cheol (SK Engineering and Construction) | Kim, Taek-Kon (SK Engineering and Construction)
ABSTRACT A new technology for storing LNG in the underground cavern has been developed by combining the concept of groundwater drainage and an ice-ring with insulation system for LNG carriers and above-ground storage tank. Formation of the ice-ring, which is one of the core technologies forming LNG storage system, can be identified by a complex mechanism undergoing between the thermal characteristics of the rock mass and hydro-geological characteristics of groundwater. The key to the technology of LNG storage system have been well demonstrated through the design, construction and operation of the Pilot Plant existing at Daejeon, Korea. The results obtained from the study with regards to the formation of the ice-ring, showed that the freezing temperature of the water flowing through rock joints is affected by the latent heat during freezing, aperture of joints and the flow rate of groundwater. In the present study, the freezing temperature and the penetration length of groundwater was investigated by a thermo-hydraulic coupled analysis and CFD analysis of the groundwater flow in the joints during formation of the ice-ring. The factors affecting the freezing temperature of groundwater during the ice-ring formation are the rate of rise in groundwater level and the joint aperture. In addition, the numerical modeling studies demonstrated that the two factors were affecting each other prominently. The freezing temperature of groundwater in both narrow and wide aperture of a joint can be applied with a value higher than −3°C, which was assumed as freezing temperature in the past. However, these numerical analyses were conducted in a limited range with several assumed conditions. Therefore, further analysis with several other conditions would be necessary to clarify the freezing temperature of groundwater in the rock joints.
Lee, Chun-Ju (Maritime & Ocean Engineering Research Institute) | Cho, Seong-Rak (Maritime & Ocean Engineering Research Institute) | Jeong, Seong-Yeob (Maritime & Ocean Engineering Research Institute) | Chun, Eun-Jee (Maritime & Ocean Engineering Research Institute)
ABSTRACT: In the near future, the number of ice-going and icebreaking vessels is expected to increase. This is linked to expected utilization of the northern sea route as an international trade route between the North Atlantic and the North Pacific region. Since many ice-going vessels are expected to be developed, increased demand for physical model testing in ice to assist vessel designers is anticipated. Various types of ice model tests will be required in order to improve the ice-going performance of these new vessels. Estimation of ship resistance in icecovered waters has been an interesting and challenging topic for ship designers. Ice resistance is dependent primarily on ice thickness and flexural strength, and the ship's operating speed. Ice resistance determines the engine power and drives the propulsion system design. This is a crucial and expensive component of an icebreaking vessel. With the support of the Korean Government, the research community and the ship building industries, MOERI decided some years ago to build the next generation ice model basin at Daejeon. The MOERI ice model basin was completed in September 2009. Since then, MOERI's ice tank has produced more than 23 ice sheets and a series of ice model test for a Korean icebreaking research vessel was conducted. In order to check the reliability and accuracy of the ice test as a whole, some comparative studies were made. The test results are compared with those conducted in Helsinki university ice model basin in 2004–2005. INTRODUCTION MOERI's ice model basin are equipped with square type basin, trimming tank, ice melting tank, thermal barrier, X-Y main carriage, service carriage and refrigeration system etc. The size of main basin is 42m long, 32m wide, 2.5m deep and various kinds of ice performance tests and full turning circle tests can be conducted.
Lee, Chun-Ju Lee (Maritime & Ocean Engineering Research Institute, KORDI) | Cho, Seong-Rak (Maritime & Ocean Engineering Research Institute, KORDI) | Jeong, Seong-Yeob (Maritime & Ocean Engineering Research Institute, KORDI) | Chun, Eun-Jee (Maritime & Ocean Engineering Research Institute, KORDI)
In the near future, the number of ice-going breakers operating in the northern sea route will be increased, as potential international trade between the North Atlantic and the North Pacific region increases. Since many ice-going breakers are expected to be developed, various kinds of ice model tests will be carried out in order to improve their ice-going capability as well as their performance. This in turn leads to increased demand for physical model testing in ice to assist a design process and to improve a vessel’s ice-going capability and performance. The estimation of a ship’s resistance in ice-covered seas has been a very interesting topic to shipbuilders. Ice resistance is related to the propulsion of a ship, and it determines the engine power of the ship. Generally, ice resistance is related to ice conditions, such as ice thickness and ice flexural strength, and its operating condition (speed). In order to check the reliability and the accuracy of the ice test as a whole, some comparative studies were made. With the support of the Korean Government, the research community, and the ship-building industries, MOERI decided to build the next generation ice model basin at Daejeon. The MOERI ice model basin was completed at the end of September 2009 (see Figure 1). Since 2009, MOERI’s ice tank has produced more than 20 ice sheets, and a series of ice model tests for the Korean icebreaking research vessel was conducted. The test results are compared with those conducted in the Helsinki university ice model basin in 2004-2005.
Shen, B. (CSIRO Exploration and Mining) | Kim, H.M. (Korea Institute of Geoscience & Mineral Resources) | Park, E.S. (Korea Institute of Geoscience & Mineral Resources) | Kim, T.K. (SK E&C) | Lee, J.M. (SK E&C) | Lee, H.S. (SK E&C) | Junker, R. (Leibniz Institute for Applied Geosciences (LIAG)) | Rinne, M. (FRACOM Ltd) | Backers, T. (GeoFrames GmbH) | Meier, T. (GeoFrames GmbH) | Stephansson, Ove (Helmholtz Center)
Abstract The paper describes a recent numerical code development and laboratory investigations on coupled thermal-mechanical processes of rock fracture propagation. The numerical development is based on a fracture mechanics code FRACOD that has previously been developed by some of the authors of this paper. The code simulates complex fracture propagation in rocks governed by both tensile and shear mechanisms. For the latest development an indirect boundary element method, namely the fictitious heat source method, is implemented in FRACOD to simulate the temperature change and thermal stresses in rocks. This method is particularly suitable for the thermal-mechanical coupling in FRACOD where the displacement discontinuity method is used for mechanical simulation. The coupled code has also been extended to simulate multiple region problems with different thermal and mechanical properties. This paper also describes the recent laboratory investigations on rock strength and fracture toughness within a temperature range from -60°C to 250°C. An application case is presented where a pilot LNG underground cavern operated by SKEC at Daejeon, South Korea is studied using the coupled code. The code simulates the cases where excavation, concrete lining and thermal insulation layer are all present. A good agreement has been obtained between the FRACOD simulation and the actual field measurement data in the pilot LNG cavern. INTRODUCTION Geothermal energy extraction Geological CO2 sequestration Underground LNG storage Deep geological disposal of nuclear waste Coal bed gas extraction With increasing concerns about environmental issues related to the mining and energy sector worldwide, the field of rock mechanics is being advanced and widened to address the complex behaviour of mechanical, thermal, hydraulic and chemical responses of rocks. Over the past several decades, coupled M (mechanical) – T (thermal) – H (hydraulic) – C (chemical) processes in rock masses have been a focus of research, particularly in the field of underground nuclear waste disposal, and significant advances have been achieved . The past studies however have mostly treated the rock mass as a continuum, or a discontinuum with predefined discontinuities. The process of explicit rock fracturing, which is the dominant mechanism in hard rock failure, has not been adequately addressed during the simulation of complex coupled processes. Understanding and predicting the effects of the interactive processes between explicit rock fracturing, temperature change and fluid flow or F (fracturing) –T (thermal) – H (hydraulic) processes, remains to be a key challenge for industries such as:To address the issues mentioned above, an international collaboration project has been established which is participated by CSIRO (Australia), SKEC (S Korea), KIGAM (S Korea), LIAG (Germany), GeoFrames GmbH (Germany) and FRACOM (Finland). The aim of this project is to develop knowledge and numerical tools that help to understand the F-T-H process of rocks on engineering scales. This paper reports the first part of the study , namely experimental evidence and simulations of Coupled Fracture (F) - Thermal (T) processes. DEVELOPMENT OF COUPLED F-T CODE A two-dimensional fracture propagation code, FRACOD, was developed by Shen and Stephansson  and FRACOM .
Didier, C. (INERIS) | Van Der Merwe, J.N. (Bon-Terra Mining (Pty) Ltd) | Betournay, M. (CANMET) | Mainz, M. (IHS Consulting, Germany) | Aydan, O. (Tokai University) | Song, W-K. (KIGAM) | Kotyrba, A. (Central Mining Institute,) | Josien, J-P. (GEODERIS)
ABSTRACT In 2005, Prof. Nielen Van der Merwe, at that time President of the ISRM, initiated a commission to facilitate the constitution of an international network of experts involved in mine closure and post-mining management. Eight experts coming from different countries have been deeply involved in this ISRM "mine closure commission", for four years. Closure of mining operations does not lead to the complete elimination of risks likely to affect the surface above old mine workings. Therefore, disorders potentially harmful for people and goods may develop, sometimes just after the closure but also, in some cases, long time after. The first mandate of the commission has been dedicated to the elaboration of a state-of-the- art report presenting, at an international scale, the mine closure problem (context, main risks of disorders, major hazard assessment methods and treatment techniques). The present paper presents an outline of this ISRM report that members may download on the ISRM website. 1 INTRODUCTION 1.1 Commission constitution and objectives The mine closure Commission has been appointed with two main objectives. The first one was to facilitate contacts between experts in rock mechanics from different countries concerned with post mining management in order to create opportunities to exchange experiences, case studies and scientific data. The second objective of the commission was to elaborate a reference document, presenting the international "state-of-the-art" for existing techniques and methods enabling identification, characterisation and management of geotechnical hazards related to mine closure processes (Didier et al., 2008). An expert panel has thus been constituted to elaborate the document. All the members that joined the commission got involved on a strictly voluntary basis and gave considerably of their time and their expertise to the benefit of the commission work. They are listed below:Christophe DIDIER, INERIS, Verneuil-en-Halatte, France. President of the Commission. Nielen Van der MERWE, Bon-Terra Mining Ltd, South-Africa. Past President of the ISRM. Ömer AYDAN, Tokaï University, Shizuoka, Japan. Marc BÉTOURNAY, CANMET, Mining and Mineral Sciences Laboratories, Ottawa, Canada. Jean-Pierre JOSIEN, GEODERIS, Metz, France. Andrej KOTYRBA, Central Mining Institute, Katowice, Poland. Mark MAINZ, IHS (Ingenieurbuero Heitfeld- Schetelig), Aachen, Germany. Won-Kyong SONG, Korea Instit. of Geoscience and Min. Resources, Daejeon, Korea. 1.2 Content of the report The mine closure state-of-the-art report contains 7 sections and 3 appendices. After a brief presentation of the mine closure context, at an international scale, the document describes precisely the most frequent geomechanical hazards that may develop above an abandoned mine. In addition to the description of consequences and potential effects on people and surface structures, the basic mechanisms that may initiate the failure are discussed. The commonly used hazard assessment methods are then described, with a particular attention to the key factors that have to be taken into account in the assessment process. Classical post-mining risk management methods are then discussed: voids treatment, monitoring methods, land use management. Specific references are included at the end of each section and recommended additional literature is also given.
Park, C. (Korea Institute of Geoscience & Mineral Resources ) | Cheon, D.S. (Korea Institute of Geoscience & Mineral Resources ) | Chung, S.K. (Korea Institute of Geoscience & Mineral Resources ) | Lim, H.D. (Chungnam National University ) | Park, Y.J. (University of Suwon )
ABSTRACT: A new concept storing LNG in a hard rock lined cavern have been developed and tested for several years in Korea. In design and construction of underground storage for LNG, it is very important to evaluate the characteristics of the rock mass under cryogenic conditions. In this study, laboratory experiments for the measurement of the mechanical properties such as uniaxial compressive strength, tensile strength, fracture toughness were performed in the temperature range of -60°C to 20°C. And an expansion pressure and cryo-suction related to ice ring formation were also measured. Experiment results show that uniaxial compressive strength, tensile strength, fracture toughness increased with decreasing temperature, but elastic modulus changed little with decreasing temperature. The expansion pressure was approximately 2.43 MPa at the phase change temperature. In the cryosuction test, the growth rate of the ice in joints was 1.0 mm/day to 1.1 mm/day. The results of this study can be utilized for the evaluation of technical feasibility of the developed underground LNG storing concept. 1. INTRODUCTION Some attempts have been made to store LNG underground in unlined containment but were not successful. Underground storage failures were due to thermal stresses generating cracks in the host soil and thermal cracks contributed to induce gas leakage and to an increase in heat flux between LNG and the ground (Kim, Amantini & Chanfreau, 2003). In order to overcome to the problems, a new concept storing LNG in a hard rock lined cavern have been developed and tested for several years. In this concept, groundwater in rock mass around cavern has to be fully drained until early stage of construction and operation to avoid possible adverse effect of groundwater near cavern walls. And then rock mass should be re-saturated to form an Ice- ring (Figure 1), which is frozen zone including ice in several joints within rock mass. To verify the technical all aspects for the concept, a pilot plant has been constructed and tested in Daejeon since 2003 by storing liquefied nitrogen, LN2(Figure 2), which is an alternative of LNG for safe operation. When considering the stability of underground storage for LNG, it is necessary to study the formation mechanism and extent of the Ice-ring which the frozen including ice in several joints within the rock mass. However, little research exists on Ice-ring formation and the thermo-mechanical behaviour of rock exposed to cryogenic conditions. In this paper, in order to investigate mechanical and thermo-mechanical characteristics of rock caused by cooling, several tests were conducted on granite sampled from a LNG pilot plant. Thermo-mechanical tests, such as the uniaxial compressive test and the Brazilian test, were conducted in the temperature range of -60°C to 20°C. And In order to analyze the effect of the phase change of water to ice, the expansion pressure caused by the phase change of water to ice were measured. The cyro-suction test was performed to investigate the flow characteristics after ice formation. 2. ROCK SPECIMENS The rock specimen used in the experiment is biotitic granite, which is sampled from LNG pilot plant. Mechanical and thermal properties of tested rocks are summarized in table 1.
Chung, S.K. (Korea Institute of Geoscience and Mineral Resources ) | Park, E.S. (Korea Institute of Geoscience and Mineral Resources ) | Lee, D.H. (SK Engineering & Construction Co. Ltd. ) | Kim, H.Y. (SK Engineering & Construction Co. Ltd. )
ABSTRACT: In order to secure large LNG (liquefied natural gas) storage facilities and to stabilize the LNG supply on a long term basis, a new system of storing LNG in a lined rock cavern has been developed. The concept consists of protecting the host rock against the extremely low temperature by using a containment system with a gas tight steel liner and insulation panels. Moreover, the moderated and controlled frost development in the surrounded rock mass contributes to create an ice ring, acting as a secondary barrier against any possible leakage. Therefore, the location and thickness of the ice ring are important factors for the stability of the underground LNG storage in a lined rock cavern. This paper describes the results of the numerical modeling performed to investigate the impact of ice ring formation and propagation on the ground water flow, where the ice ring is formed by the phase change of groundwater due to the cooling-down in the rock mass around the cavern. The results of the numerical simulation showed that the process of ice ring formation was similar to the one evaluated by the interpretation from the geophysical survey data during the pilot operation. 1. INTRODUCTION Many attempts have been made to store LNG in unlined rock caverns but were not successful. The failures were due to thermal stresses generating cracks in the host rock and the thermal cracks contributed to deteriorating the operational efficiency of the cavern because of induced gas leakage and increased heat flux between ground and storage [1, 2]. To provide a safe and cost-effective solution, a new concept of storing LNG in a lined hard rock cavern has been developed and tested for several years . The concept consists of protecting the host rock against the extremely low temperature by using a containment system with a gas tight steel liner and insulation panels. Moreover, the moderated and controlled frost development in the surrounded rock mass contributes to create an ice ring, acting as a secondary barrier against any possible leakage (Fig. 1). Therefore, the location and thickness of the ice ring are important factors for the stability of the underground LNG storage in a lined rock cavern. In order to verify the technical feasibility of such storage concept, a pilot plant was constructed in the Daejeon Science Complex in 2003. From January through August 2004, a pilot test has been performed using LN2 (liquid nitrogen) instead of LNG for safety and practical reasons . Fig. 1. Concept of LNG storage in a lined rock cavern. (available in full paper) The main purpose of this paper is to understand mechanism related with ice ring formation during the stop period of the drainage system in rock mass around the pilot cavern after six months of cooling-down. So behavior of rock mass and structures associated with heat transfer, groundwater flow and ice ring formation is simulated with a CFD code, FLOW3D.
Chung, S.-K. (Korea Institute of Geoscience and Mineral Resources (KIGAM)) | Park, E.-S. (Korea Institute of Geoscience and Mineral Resources (KIGAM)) | Kim, H.-Y. (SK Engineering & Construction Co., Ltd.,) | Lee, H.-S. (SK Engineering & Construction Co., Ltd.,) | Lee, D.-H. (SK Engineering & Construction Co., Ltd.,)
ABSTRACT: To provide a safer and cost effective solution, a new concept of storing liquefied natural gas (LNG) in a lined rock cavern with containment system has been developed. It consists of protecting the host rock against the extremely low temperature and providing a liquid and gas tight steel liner. Moreover, the moderated and controlled frost development in the surrounded rock mass contributes to creating an ice ring, which acts as a secondary barrier against any possible leakage. To demonstrate the feasibility of this concept and to validate the numerical modeling and calculations, a pilot plant was constructed at KIGAM in the Daejeon Science Complex in 2003, which had been under operation for storing LN2 (Boiling Temperature: −196°C) since January 2004, and now been decommissioned. In this paper, measured in-situ rock mass responses from the operation of Daejeon LNG storage pilot cavern are presented and analyzed on rock mechanical point of view. The obtained results from the pilot test confirmed that both construction and operation of underground LNG storage in lined rock caverns are technically feasible. The Daejeon LNG storage pilot cavern represents a further important step in the validation of the technology of underground LNG storage in the lined rock caverns. 1 INTRODUCTION To provide a safe and cost-effective solution, a new concept of storing LNG in a lined hard rock cavern (LRC) has been jointly developed by Geostock, SKEC and SNTechnigaz with the help of KIGAM. The basic concept is based on the combination of a containment system to ensure for LNG with rock protection against thermal shock and a drainage system during the early months of the storage operation and before the freezing of the surrounding rock. It consists of protecting the host rock against the extremely low temperature by using a containment system with gas-tight steel liners and insulation panels as illustrated in Figure 1. 2 OVERVIEW OF THE PILOT CAVERN 2.1 The Daejeon pilot plant for storing LNG In order to verify the technical feasibility of such a storage concept, a pilot plant was constructed in 2003 and had been operated by storing liquid nitrogen (LN2, Boiling Temperature: −196°C) since from January through August, 2004. The cavern has, more recently, been decommissioned. The pilot cavern is located in Daejeon, about 200 km south from Seoul, in an existing research cavern implemented within the KIGAM research facilities. Figure 2 shows a bird's-eyeviewof the pilot cavern for LNG storage.The rock type around the cavern mainly consists of fresh granite with RQD of 80–86 and with the most frequent Q value of 12.5. Therefore, it is proper to adapt rock bolting to stabilize main cracks of the existing cavern and ensure the stability of possible crack position. The access to the pilot cavern was provided through an existing horizontal tunnel and the cavern roof lies at a depth of about 20m below the ground.