• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.3
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• pp.263-273
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• 2007

When a tunnel or an underground structure is excavated in deep geological environments, the failure process is affected and eventually dominated by stress-induced fractures growing preferentially parallel to the excavation boundary. This fracturing is generally referred to as brittle failure by spatting and slabbing. Continuum models with traditional failure criteria such as Hoek-Brown or Mohr-Coulomb criteria have not been successful in prediction of the extent and depth of brittle failure. Instead cohesion weakening and frictional strengthening (CWFS) model is known to predict brittle failure well. In this study, CWFS model was applied to predict the brittle failure around a circular opening observed in physical model experiments. To obtain the input parameters for CWFS model, damage-controlled tests were carried out. The predicted depth and extent of brittle failure using CWFS model were compared to the results of the physical model experiment and numerical simulation using traditional model.

• The Journal of Engineering Geology
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• v.20 no.4
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• pp.359-370
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• 2010

$CO_2$ leakage from a geological formation utilized for $CO_2$ storage could result in failure of the facility and threaten the environment, as well as human safety and health. A reactive transport model of a $CO_2-H_2O$-cement reaction was constructed to understand chemical changes in the case of $CO_2$ leakage through a cement crack in an injection well, which is the most probable leakage pathway during geological storage. The model results showed the dissolution of portlandite and CSH (calcium silicate hydrate) within the cement paste, and the precipitation of secondary CSH and calcite as the $CO_2$ plume migrated along the crack. Calcite occupied most of the crack after 3 year of reaction, which could be maintained until 30 years after crack development. The present results could be applied in the development of technology to prevent $CO_2$ leakage and to enhance the integrity of wells constructed for $CO_2$ geological storage.

• Steel and Composite Structures
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• v.2 no.3
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• pp.171-194
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• 2002

In this paper, the behaviour of axially loaded partially encased composite columns made with light welded H steel shapes is examined using ABAQUS finite element modelling. The results of the numerical simulations are compared to the response observed in previous experimental studies on that column system. The steel shape of the specimens has transverse links attached to the flanges to improve its local buckling capacity and concrete is poured between the flanges only. The test specimens included 14 stubcolumns with a square cross section ranging from 300 mm to 600 mm in depth. The transverse link spacing varied from 0.5 to 1 times the depth and the width-to-thickness ratio of the flanges ranged from 23 to 35. The numerical model accounted for nonlinear stress-strain behaviour of materials, residual stresses in the steel shape, initial local imperfections of the flanges, and allowed for large rotations in the solution. A Riks displacement controlled strategy was used to carry out the analysis. Plastic analyses on the composite models reproduced accurately the capacity of the specimens, the failure mode, the axial strain at peak load, the transverse stresses in the web, and the axial stresses in the transverse links. The influence of applying a typical construction loading sequence could also be reproduced numerically. A design equation is proposed to determine the axial capacity of this type of column.

• Ocean and Polar Research
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• v.38 no.1
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• pp.71-79
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• 2016

In this study, we attempt to examine the economic impacts of the CCS marine geological storage demonstration project in Korea using Input-Output analysis utilizing the inter-industry relation table issued in 2013. In particular, this study defines the $CO_2$ ocean storage industry and then added the inter-industry relation table and treated the $CO_2$ ocean storage industry as exogenous. In addition, this study assumed two scenarios based on the means of $CO_2$ transport, which are pipe and ship. After defining the industry and scenarios, this study investigates the production-inducing effect, value added inducing effect, and employment-inducing effect of the industries associated with the $CO_2$ ocean storage industry based on a demand-driven model. The results pertaining to the scenarios are estimated as follows: total production-inducing effects, value added inducing effects, and employment-inducing effects are calculated as 1.9044 won, 1.2487 won and 16.7224 people/billion won, respectively. In addition, compared to other industries, the indirect economic impacts of the $CO_2$ ocean storage industry are ranked high: the rankings of production-inducing effects, value added inducing effects, and employment-inducing effects are fourth, second, and fifth, respectively.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.275-291
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• 2019

In a super-large underground with "large span and high side wall", it is buried in mountains with uneven lithology, complicated geostress field and developed geological structure. These surrounding rocks are more susceptible to stability issues during the construction period. This paper takes the left bank of Baihetan hydropower station (span is 34m) as a case study example, wherein the deformation mechanism of surrounding rock appears prominent. Through analysis of geological, geophysical, construction and monitoring data, the deformation characteristics and factors are concluded. The failure mechanism, spatial distribution characteristics, and evolution mechanism are also discussed, where rock mechanics theory, $FLAC^{3D}$ numerical simulation, rock creep theory, and the theory of center point are combined. In general, huge underground cavern stability issues has arisen with respect to huge-scale and adverse geological conditions since settling these issues will have milestone significance based on the evolutionary pattern of the surrounding rock and the correlation analyses, the rational structure of the factors, and the method of nonlinear regression modeling with regard to the construction and development of hydropower engineering projects among the worldwide.

• Earthquakes and Structures
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• v.24 no.1
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• pp.53-64
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• 2023

Earth fissures with several kilometers will inevitably approach or cross the metro line, significantly threatening the safety of the underground structure in the earth fissure site. However, the influence of the earth fissure site's amplification effect on the metro station's dynamic response is still unclear. A representative earth fissure in Xi'an was taken as an example to establish a numerical model of a metro station in the earth fissure site. The dynamic response characteristics of the metro stations at different distances from the earth fissure under various seismic waves were calculated. The results show that the existence of the earth fissure significantly amplifies the dynamic response of the nearby underground structures. The responses of the axial force, shear force, bending moment, normal stress, horizontal displacement, inter-story drift, and relative slip of the metro station were all amplified within a specific influence range. The amplification effect increases with the seismic wave intensity. The amplification effect caused by the earth fissure has relatively weak impacts on the axial shear, shear force, bending movement, normal stress, and horizontal movement; slightly larger impacts on the inter-story drift and acceleration; and a significant impact on the relative slip. The influence ranges of the axial force and normal stress are approximately 20 m. The influence ranges of the acceleration and inter-story drift can reach 30 m. Therefore, the seismic fortification level of the underground structure in the earth fissure site needs to be improved.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.1
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• pp.23-41
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• 2023

Coupled thermo-hydraulic-mechanical (THM) processes are essential for the long-term performance of deep geological disposal of high-level radioactive waste. In this study, a numerical sensitivity analysis was performed to analyze the effect of rock properties on THM responses after the execution of the heater test at the Kamaishi mine in Japan. The TOUGH-FLAC simulator was applied for the numerical simulation assuming a continuum model for coupled THM analysis. The rock properties included in the sensitivity study were the Young's modulus, permeability, thermal conductivity, and thermal expansion coefficients of crystalline rock, rock salt, and clay. The responses, i.e., temperature, water content, displacement, and stress, were measured at monitoring points in the buffer and near-field rock mass during the simulations. The thermal conductivity had an overarching impact on THM responses. The influence of Young's modulus was evident in the mechanical behavior, whereas that of permeability was noticed through the change in the temperature and water content. The difference in the THM responses of the three rock type models implies the importance of the appropriate characterization of rock mass properties with regard to the performance assessment of the deep geological disposal of high-level radioactive waste.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.3
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• pp.239-256
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• 2017

In the process of site selection for a radioactive waste disposal, site characterization must be carried out to obtain input parameters to assess the safety and feasibility of deep geological repository. In this paper, methodologies of site characterization for radioactive waste disposal in Korea were suggested based on foreign cases of site characterization. The IAEA recommends that site characterization for radioactive waste disposal should be performed through stepwise processes, in which the site characterization period is divided into preliminary and detailed stages, in sequence. This methodology was followed by several foreign countries for their geological disposal programs. General properties related to geological environments were obtained at the preliminary site characterization stage; more detailed site characteristics were investigated during the detailed site characterization stage. The results of investigation of geology, hydro-geology, geochemistry, rock mechanics, solute transport and thermal properties at a site have to be combined and constructed in the form of a site descriptive model. Based on this site descriptive model, the site characteristics can be evaluated to assess suitability of site for radioactive waste disposal. According to foreign site characterization cases, 7 or 8 years are expected to be needed for site characterization; however, the time required may increase if the no proper national strategy is provided.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.4
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• pp.251-257
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• 2011

In the present study, a 3-dimensional (3D) numerical model was developed to mimic the micro porous structure of a geological $CO_2$ storage reservoir. Especially, 3D modeling technique assigning random pore size to a 3D micro porous structure was devised. Numerical method using CFD (computational fluid dynamics) was applied for the 3D micro porous structure to calculate supercritical $CO_2$ flow field. The three different configurations of 3D micro porous model were designed and their flow fields were calculated. For the physical conditions of $CO_2$ flow, temperature and pressure were set up equivalent to geological underground condition where $CO_2$ fluid was stored. From the results, the characteristics of the supercritical $CO_2$ flow fields were scrutinized and the influence of the micro pore configuration on the flow field was investigated. In particular, the pressure difference and consequent $CO_2$ permeability were calculated and compared with increasing $CO_2$ flow rate.

• Tunnel and Underground Space
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• v.29 no.5
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• pp.356-366
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• 2019

Various TBM performance prediction models have been developed and most of them were considered penetration rate only. Despite the fact that some models have suggested equations and charts for estimating the utilization factor, but there are a few studies to estimate the TBM utilization factor. Utilization factor is affected by the type of TBM machine, operation, maintenance of machine, geological conditions, contractor experience and other factors. In this study, more than 100 case studies are analyzed to determine the relationship between the utilization factor and RMR, geological conditions, TBM types, tunnel length, and TBM diameter. Simple and multiple linear regression analysis are performed to develop predictive models for the utilization factor. The predictive model with explanatory variables of geological conditions, TBM types, tunnel length, and TBM diameter does not give a good correlation. The predictive models with explanatory variable of RMR give higher values of the coefficient of determination.