• Explosives and Blasting
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• v.27 no.1
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• pp.21-31
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• 2009

An excavation damaged zone (EDZ) is created by fracturing, excavation or stress redistribution of tunnels. In this zone the mechanical and hydraulic properties of rock are changed, which makes additional cracks and serves as a dominant pathway of groundwater flow. In this study, an assessment on an EDZ size was practiced by the measurement of the deformation modulus at the KAERI underground research tunnel (KURT), and the information was applied to the modelling analysis using FLAC2D software. The EDZ at KURT fell into the range of 0.6~1.8m and the deformation moduli of the EDZ generally correspond to about 40% of intact rock mass. With a consideration of the EDZ in numerical analysis, tunnel displacements increased by about 65% and the maximum principal stress decreased to 58% from the case without EDZ. The plastic zone of the tunnel was enlarged to the crown and invert zones of the tunnel within the range of the length of rock bolts. About 2% of the total tunnel displacement with EDZ was suppressed by the KURT support system. It is anticipated that the investigation of an EDZ can be used as an important and fundamental research for validating the overall performance of a high level waste disposal system.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.54-70
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• 2024

Utilization of completed open-pit for mining waste disposal is an alternative method of tailing storage facility (TSF), which can minimize the area and cost required for the installation of TSF. However, long-term tailing disposal into open-pit has a potential risk of reducing mechanical stability of surrounding rock mass by acting as an additional load. In this research, a realistic open-pit tailing disposal scenario of 60,400 hours was established based on the case of Marymia gold mine, Australia. Mechanical stability of surface pillar between open-pit and underground stope was analyzed numerically by using Sigma/W, under different stope geometry and rock mass conditions. Simulation results showed that long-term tailing disposal into open-pit can significantly increase the failure probability of surface piller. This result suggests that mechanical stability of mine geometry should be conducted beforehand of open-pit tailing disposal.

• Tunnel and Underground Space
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• v.34 no.1
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• pp.71-87
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• 2024

In deep geological disposal of high-level radioactive waste, the surrounding rock at the immediate vicinity of the deposition hole may experience localized changes in permeability due to in-situ stress at depth, swelling pressure from resaturated bentonite buffer, and the heat generated from the decay of radioactive isotopes. In this study, experimental data on changes in permeability of granite, a promising candidate rock type in South Korea, were obtained by applying various confining pressures and temperature conditions expected in the actual disposal environment. By conducting the permeability test on KURT granite specimens under three or more hydrostatic pressure conditions, the relation in which the permeability decreases exponentially as the confining pressure increases was derived. The temperature-induced changes in permeability were found to be negligible at temperatures below the expected maximum of 90℃. In addition, by establishing a relation in which the initial permeability is proportional to the power of the initial porosity, it was possible to estimate permeability value for granite with a specific porosity under a certain confining pressure.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.89-95
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• 2009

The current enforce decree of "The Act on the Promotion of Construction Waste Recycling" divides seventeen kinds of construction wastes by property and configuration. Mixed construction waste, one of them classified by the enforce decree, is composed two more than justified construction wastes except refuse soil and rock. In construction wastes justified by enforce decree of this law, most refuse concrete and asphalt concrete of construction wastes are recycled. As well as refuse metal is separated, sorted from bulk them, and merchandised for value. Finally this is used the secondary manufactured products. Even though combustible construction wastes like refuse wood, plastics, fiber can be recycled RDF(Refuse derived fuel) or RPF(Refuse plastic fuel) because of high caloric value and low heavy metal but most of them are discharged as mixed construction waste and then treated by treated by incineration and landfill. Therefore, to control construction waste flow efficiently, construction wastes are classifies first combustible, incombustible, mixed combustible, incombustible and etc. in this study. The combustible waste is consisted refuse wood, plastics, fiber and etc. and incombustible waste contains refuse concrete, asphalt, and etc. Mixed construction is construction waste that can not separate from mixed waste bulk with different kinds.

• Journal of the Korean GEO-environmental Society
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• v.12 no.12
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• pp.71-78
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• 2011

This paper aims to present the evaluation of engineering characteristics and reusing possibility of waste powders produced in dolomite and limestone nonmetal mining by physical and mechanical experiments on compaction, uniaxial compressive strength, permeability, chemical composition, and so on. Granite soil, 2 types of limestone waste powder, and 1 type of dolomite waste powder were used for main materials, and cement and bentonite were used for admixed materials in this experiments. The findings based on the experimental results are the severe difference of chemical composition of the dolomite & limestone waste powder and the crushed rock waste powder, and the outstanding of engineering characteristics of the dolomite waste powder with high content of MgO compared with the limestone waste powder. The engineering properties on compaction, uniaxial compressive strength, and permeability are enhanced with increase of admixed ratio of waste powder on granite soil. From the experimental results, it can be suggested that the dolomite waste powder admixed with in-situ granite soil is useful as geo-materials with considering of distribution costs.

• The Journal of Engineering Geology
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• v.20 no.2
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• pp.213-220
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• 2010

The permeability characterization on the natural barrier for deep geological disposal of radioactive waste is very critical to evaluate total safety and performance assessment of disposal site. However, the confidence level in using previous hydraulic testing equipments consist of simple components to estimate rock mass permeability is not high enough to reflect in situ condition. The purpose of this research is to establish an advanced hydraulic testing equipment, which is applicable to deep borehole (up to 1,000 m), through the improvement of technical problems of previous packer systems. Especially, the straddle packer hydraulic testing equipment was designed to adopt both the hydraulic downhole shut-in valve(H-DHSIV) to minimize the wellbore storage effect and the real time data acquisition system to measure the pressure changes of test interval including its upper and lower parts. The results from this research lead to not only improve current technical level in the field of hydraulic testing but also provide important information to radioactive waste disposal technology development and site characterization project.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.325-330
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• 2016

The second phase of low- and intermediate-level waste (LILW) disposal facility is under planned on the sedimentary rock in unsaturated zone. In this study, we created two meshes which were a matrix continuum mesh and a fracture continuum mesh to carry out 2 dimensional numerical modeling for groundwater flow in the unsaturated zone containing fractures focused on the second phase of LILW disposal facility. Two continuum meshes were developed using MINC in meshmaker module of TOUGH2 code. A fracture continuum mesh was included the k-field distribution of the permeability derived from the Discrete Fractured Network (DFN) modeling. To apply the unsaturated zone for the modeling, the gridding steps to generate mesh were developed. Each step to generate a mesh consisted of definition of materials, setting the initial conditions and creating grids using MINC. The methodology development of meshes in this study will be applied for more precise modeling of groundwater flow and mass transport.

• Tunnel and Underground Space
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• v.30 no.4
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• pp.382-393
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• 2020

The engineered barrier system of high-level radioactive waste disposal must maintain its performance in the long term, because it must play a role in slowing the rate of leakage to the surrounding rock mass even if a radionuclide leak occurs from the canister. In particular, it is very important to clarify gas dilation flow phenomenon clearly, that occurs only in a medium containing a large amount of clay material such as a bentonite buffer, which can affect the long-term performance of the bentonite buffer. Accordingly, DECOVALEX-2019 Task A was conducted to identify the hydraulic-mechanical mechanism for the dilation flow, and to develop and verify a new numerical analysis technique for quantitative evaluation of gas migration phenomena. In this study, based on the conventional two-phase flow and mechanical behavior with effective stresses in the porous medium, the hydraulic-mechanical model was developed considering the concept of damage to simulate the formation of micro-cracks and expansion of the medium and the corresponding change in the hydraulic properties. Model verification and validation were conducted through comparison with the results of 1D and 3D gas injection tests. As a result of the numerical analysis, it was possible to model the sudden increase in pore water pressure, stress, gas inflow and outflow rate due to the dilation flow induced by gas pressure, however, the influence of the hydraulic-mechanical interaction was underestimated. Nevertheless, this study can provide a preliminary model for the dilation flow and a basis for developing an advanced model. It is believed that it can be used not only for analyzing data from laboratory and field tests, but also for long-term performance evaluation of the high-level radioactive waste disposal system.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.4
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• pp.273-281
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• 2007

Hyperalkaline groundwater formed by groundwater-cement components and its reaction with bedrock in a nuclear waste repository were simulated by geochemical modeling. The result of groundwater-cement components reaction showed that the pH of water was 13.3 and the precipitated minerals were Brucite, Katoite, Calcium Silicate Hydrate(CSH1.1), Ettringite, Hematite, and Portlandite. The result of interaction between such minerals and groundwater sampled in Gyeongju area also showed that the pH of groundwater reached 12.4. Interaction between such hyperalkaline groundwater and granite was simulated by kinetic model during $10^3$ years. This result showed that the final pH of groundwater reached 11.2 and the variation of pH was controlled by dissolution/precipitation of silicate and CSH minerals. Groundwater quality was also determined by dissolution/precipitation of silicate, CSH, oxide minerals. Our results show that geochemical modeling of long-term hyperalkaline groundwater and rock interaction can contribute to the safety assessment of engineered barrier by predicting geochemical condition in repository site.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.1
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• pp.9-15
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• 2006

For the accurate safety assessment of potential radioactive waste disposal site which is located in the crystalline rock it is important to simulate the mass transportation through engineered and natural barrier system precisely, characterized by porous and fractured media respectively. In this work the methods to construct discrete fracture network for the analysis of flow and mass transport through fractured-porous medium are described. The probability density function is adopted in generating fracture properties for the realistic representation of real fractured rock. In order to investigate the intersection between a porous and a fractured medium described by a 2 dimensional rectangular and a cuboid grid respectively, an additional imaginary fracture is adopted at the face of a porous medium intersected by a fracture. In order to construct large scale flow paths an effective method to find interconnected fractures and algorithms of swift detecting connectivities between fractures or porous medium and fractures are proposed. These methods are expected to contribute to the development of numerical program for the simulation of radioactive nuclide transport through fractured-porous medium from radioactive waste disposal site.