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Numerical simulation of fracture mechanics and thermo-mechanical behaviour under low temperature conditions
Tunnelling and Underground Space Technology Tunnelling and Underground Space Technology 21 (2006) 470–471
incorporating Trenchless Technology Research
www.elsevier.com/locate/tust
Numerical simulation of fracture mechanics and thermo-mechanical behaviour under low temperature conditions Yang-Soo Jeon a, Eui-Seob Park a, So-Keul Chung a, Dae-Hyuck Lee b, Ho-Young Kim a
b
Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea b SK Engineering & Construction Co. Ltd., Seoul, Republic of Korea
One of the important problems related to underground storage of cryogenic material is to prevent leakage of liquid and gas from containment system to the rock mass that might be caused by tensile stresses due to shrinkage of the rock mass around the caverns. If the storage is unlined and frozen down to 162 °C due to LNG storing, a part of the gas flows into the joints and continues to cool down inside the rock wall when the rock is cooled and the rock joints start to open. This will successively open the joints and heavily increase the cooled area and the extent of the cooling front. To provide a safe and cost-effective solution, a new idea of storing LNG in a lined hard rock cavern has been developed and tested for several years. This concept consists of protecting the host rock against the cryogenic temperature by using a containment system with gas tight steel liner and insulation panels. The pilot project of lined cavern LNG storage has been carried out in an existing research cavern in Korea. The objective of this project is to demonstrate the feasibility of the lined rock cavern concept. For the safety and practical reasons, liquid nitrogen (LN2, T = 196 °C) is used instead of LNG. In this paper, thermo-mechanical analyses were performed in two different ways: (a) fracture mechanical approach with greatly simplified model using PFC 2D, (b) 2-dimensional numerical modeling to a lined LNG rock pilot cavern with UDEC. An important goal of PFC 2D simulation was to investigate the effect of joint and frost heave pressures on the formation of new cracks during cooling. On the basis of the results from thermo-mechanical modeling using a PFC 2D code, it is certain that presence of joints and frost heave pressure had a pronounced effect on the formation of new cracks in the rock mass. A comprehensive monitoring system was applied during implementation of LNG storing. After 6 months of cooling (before LN2 filling stop), the 0 °C isothermal propagated up to 4.4 m from the cavern floor, 4.0 m from the sidewall. In this paper, in situ measured rock mass responses from the operation of LNG pilot cavern are presented and compared to the results of numerical analyses. Thermal and mechanical responses of the rock mass around the LNG storage cavern could be well predicted by UDEC numerical models. The results of UDEC analyses are summarized as follows: (1) Thermal and mechanical responses of the rock mass around the LNG storage cavern could be well predicted by numerical models. (2) There was no conspicuous difference with the presence of joints. (3) The extent of 0 °C isotherm was increased with decreasing thermal properties.
doi:10.1016/j.tust.2005.12.107
Abstracts / Tunnelling and Underground Space Technology 21 (2006) 470–471
Keywords: Underground storage; LNG; Thermo-mechanical analyses
471
incorporating Trenchless Technology Research
www.elsevier.com/locate/tust
Numerical simulation of fracture mechanics and thermo-mechanical behaviour under low temperature conditions Yang-Soo Jeon a, Eui-Seob Park a, So-Keul Chung a, Dae-Hyuck Lee b, Ho-Young Kim a
b
Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea b SK Engineering & Construction Co. Ltd., Seoul, Republic of Korea
One of the important problems related to underground storage of cryogenic material is to prevent leakage of liquid and gas from containment system to the rock mass that might be caused by tensile stresses due to shrinkage of the rock mass around the caverns. If the storage is unlined and frozen down to 162 °C due to LNG storing, a part of the gas flows into the joints and continues to cool down inside the rock wall when the rock is cooled and the rock joints start to open. This will successively open the joints and heavily increase the cooled area and the extent of the cooling front. To provide a safe and cost-effective solution, a new idea of storing LNG in a lined hard rock cavern has been developed and tested for several years. This concept consists of protecting the host rock against the cryogenic temperature by using a containment system with gas tight steel liner and insulation panels. The pilot project of lined cavern LNG storage has been carried out in an existing research cavern in Korea. The objective of this project is to demonstrate the feasibility of the lined rock cavern concept. For the safety and practical reasons, liquid nitrogen (LN2, T = 196 °C) is used instead of LNG. In this paper, thermo-mechanical analyses were performed in two different ways: (a) fracture mechanical approach with greatly simplified model using PFC 2D, (b) 2-dimensional numerical modeling to a lined LNG rock pilot cavern with UDEC. An important goal of PFC 2D simulation was to investigate the effect of joint and frost heave pressures on the formation of new cracks during cooling. On the basis of the results from thermo-mechanical modeling using a PFC 2D code, it is certain that presence of joints and frost heave pressure had a pronounced effect on the formation of new cracks in the rock mass. A comprehensive monitoring system was applied during implementation of LNG storing. After 6 months of cooling (before LN2 filling stop), the 0 °C isothermal propagated up to 4.4 m from the cavern floor, 4.0 m from the sidewall. In this paper, in situ measured rock mass responses from the operation of LNG pilot cavern are presented and compared to the results of numerical analyses. Thermal and mechanical responses of the rock mass around the LNG storage cavern could be well predicted by UDEC numerical models. The results of UDEC analyses are summarized as follows: (1) Thermal and mechanical responses of the rock mass around the LNG storage cavern could be well predicted by numerical models. (2) There was no conspicuous difference with the presence of joints. (3) The extent of 0 °C isotherm was increased with decreasing thermal properties.
doi:10.1016/j.tust.2005.12.107
Abstracts / Tunnelling and Underground Space Technology 21 (2006) 470–471
Keywords: Underground storage; LNG; Thermo-mechanical analyses
471