• Tunnel and Underground Space
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• v.13 no.1
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• pp.44-51
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• 2003

Changes of the hydraulic conductivity resulting from the redistribution of stresses by underground excavation are examined using the strain-dependent hydraulic conductivity modification relation, where the modulus reduction ratio and induced strain are the major parameters. The modulus reduction ratio is defined in terms of RMR(Rock Mass Rating) to represent the full gamut of rock mass condition. Though shear dilation has the effect on the modification of hydraulic conductivity, the extent of it depends on RMR When the extensional strain is applied to a fracture, the hydraulic conductivity increases with the decrease of RMR Loading configuration has the effect on the modification of hydraulic conductivity, where the differential stress mode with a magnitude of the minimum principal stress $($\sigma$_x)$ fixed and a magnitude of the maximum principal stress $($\sigma$_y)$ varied is found to exert the greatest effect on the change of hydraulic conductivity.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.69-79
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• 2008

Dokdo is a volcano edifice originating from an oceanic island that was formed around 3 million to 2.2 million years ago, and it consists of Dongdo(eastern island) and Seodo(western island). Even though Dokdo is a small volcanic island, Dokdo has infinite potential value and significant economic, social, scientific, and technical aspects due to its resources, ecological and territorial value. In addition, it is of national interest with regards to the dispute with Japan over the dominium of Dokdo. A need to evaluate the ground stability of Dokdo, especially in Dongdo, has been seriously raised recently due to the various cracks caused by the progressive weathering and corrosion. This study dealt with the geology and geological layers of Dokdo and identified the status of ground cracks as the previous research to evaluate the ground stability of zones of concern in Dongdo. Also, this study analyzed the relationships between physical and mechanical properties with rock types. The results showed that the values of rock properties in Dokdo are lower contrary to the general rocks in Korea, and tuff was especially affected by the weathering and corrosion.

• Tunnel and Underground Space
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• v.25 no.4
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• pp.332-340
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• 2015

Ground subsidence occurring in mine area can cause an enormous damage of loss of lives and properties, and a systematic survey should be conducted a series of field investigation and ground stability analysis in subsidence area. This study describes the results from field investigation and ground stability analysis in a limestone mine located in Cheongwon-gun, Chungcheongbuk-do, Korea. Rock mechanical measurements and electrical resistivity surveys are applied to obtain the characteristics of in-situ rock masses and the distribution patterns of subsurface weak zone, and their results are extrapolated in numerical analysis. From the field investigation and stability analysis, it is concluded that the subsidence occurrence in this limestone mine is caused mainly by subsurface limestone cavities.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.283-292
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• 2016

A computer program code was developed to estimate hydraulic behavior of the 2-D connected pipe network system, and implemented to evaluate the effect of joint aperture on hydraulic parameters of fractured rock masses through numerical experiments. A total of 216 stochastic 2-D DFN(discrete fracture network) blocks of $20m{\times}20m$ were prepared using two joint sets with fixed input parameters of joint orientation, frequency and size distribution. Two different cases of joint aperture variation are considered in this study. The hydraulic parameters were estimated for generated 2-D DFN blocks. The hydraulic anisotropy and the chance for equivalent continuum behavior of the DFN system were found to depend on the variability of joint aperture.

• Tunnel and Underground Space
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• v.25 no.4
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• pp.359-372
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• 2015

Rock masses include various rock discontinuities such as faults, joints, and bedding planes. These discontinuities appear as complex structures in geometry. In this study, growth patterns of fractures between two stepping shear fracture tips are numerically modeled using PFC2D (Particle Flow Code). The numerical model showed not only incipient growth of fractures at the tips of preexisting fractures but also subsequent growth of the new fractures. It is observed from all of the experiments that the incipient fractures are tensile cracks developed at $30{\sim}57^{\circ}$ to the preexisting fractures and the subsequent growth of these fractures were at low angles to the preexisting fractures this study.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.312-320
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• 2002

It is well-known that when single rock fractures undergo shear displacement, they are influenced by the boundary conditions and fracture roughness. In this case, aperture geometry will change by means of dilation due to the shear displacement. As fractures become the flow paths, fluid flow through rock fractures is affected by the void geometry. In this study, therefore, the influence of roughness on shear behavior of fractures has been investigated, and the resulting hydraulic behavior has been analyzed. In order for this study, a statistical method has been used to generate rough fractures, and they have been adopted into new conceptual models fur fracture shearing and flow calculations. The main contributions of this study are as follows: firstly, fracture shear behavior becomes less brittle with decreasing fracture roughness and increasing normal stress. Then, the characteristics of aperture distribution becomes those of roughness of fractures indicating its hydraulic significance. Finally, it is observed that with decreasing fracture roughness the breakdown of channel flow occurs more slowly.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.304-311
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• 2002

This study reports the influence of vocid geometry on fracture closure and permeability from numerical experiments. As the aperture distributions of rock fractures are characterized by statistical methods, synthetic fractures have successfully been simulated in this way. Based on the generated fracture models, models for fracture closure and flow calculation have been developed. A fracture closure model has been developed by considering the asperity compression and half-space deformation, and flow calculations have been performed using a finite difference method adopting a local cubic law. The results of numerical experiments have shown that the increase in the aperture spatial correlation leads the fracture closure and the decrease in fracture permeability to increase. Also, it has been indicated that there is an implicit relation between fracture normal stiffness and permeability. The importance of this study is to enhance the understanding the hydro-mechanical behavior of fractured rock massed due to engineering projects.

• Tunnel and Underground Space
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• v.9 no.2
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• pp.131-140
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• 1999

Although there have been lots of geological or geotechnical surveys for construction sites, most of data obtained from these surveys have not been reused properly for the future construction work due to the absence of systematic management of data management system. This research, therefore, has focused on the development of DB system, Rockmass Information Management System(RIMS), to save, manage and reuse these abandoned data, specially test data of rock and rockmass with site conditions. RIMS has not only the basic functions of inputting, modifying, and dynamic searching of data but also several data control modules which can manage, input and correct, analyse and report data. Furthermore it saves data such as strata status, laboratory test results, in-site test results, and so on using 3-dimensional data stacking up structure. It is using x, y coordinates to represent horizontal positions and depth to represent vertical position of data. With the development of RIMS, this research has analyzed and classified present conditions of data in RIMS according to region, rock type, etc.

• Tunnel and Underground Space
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• v.13 no.6
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• pp.421-433
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• 2003

Demand for limestone production from both the underground and opencast mines in Korea is gradually increasing. Increase in productivity with safe mining operations is the emphasis laid on the mining industry. KIGAM has undertaken a detailed investigation to apply RMR and Q classification system for the design of underground limestone mining operations. The field investigations were confined to the underground mines of Daesung Mining Development Co. Ltd. and Pyunghae Mines of Korean Airport Service. Modification to the standard RMR and Q for limestone mines in Korea along with the correlation between these two systems are discussed while attempts were also made to calculate the width of a safe unsupported span.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.117-127
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• 2011

The purpose of this study is to demonstrate the effect of in-situ rock stresses on the deformability and permeability of fractured rocks. Geological data were taken from the site investigation at Forsmark, Sweden, conducted by Swedish Nuclear Fuel and Waste Man-agement Company (SKB). A set of numerical experiments was conducted to determine the equivalent mechanical properties (essentially, elastic moduli and Poisson's ratio) and permeability, using a Discrete Fracture Network-Discrete Element Method (DFN-DEM) approach. The results show that both mechanical properties and permeability are highly dependent on stress because of the hyperbolic nature of the stiffness of fractures, different closure behavior of fractures, and change of fluid pathways caused by deformation. This study shows that proper characterization and consideration of in-situ stress are important not only for boundary conditions of a selected site but also for the understanding of the mechanical and hydraulic behavior of fractured rocks.