• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.7-17
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• 2011

We have developed an inversion code for three-dimensional (3D) resistivity tomography including the anisotropy effect. The algorithm is based on the finite element approximations for the forward modelling and Active Constraint Balancing method is adopted to enhance the resolving power of the smoothness constraint least-squares inversion. Using numerical experiments, we have shown that anisotropic inversion is viable to get an accurate image of the subsurface when the subsurface shows strong electrical anisotropy. Moreover, anisotropy can be used as additional information in the interpretation of subsurface. This algorithm was also applied to the field dataset acquired in the abandoned old mine area, where a high-rise apartment block has been built up over a mining tunnel. The main purpose of the investigation was to evaluate the safety analysis of the building due to old mining activities. Strong electrical anisotropy has been observed and it was proven to be caused by geological setting of the site. To handle the anisotropy problem, field data were inverted by a 3D anisotropic tomography algorithm and we could obtain 3D subsurface images, which matches well with geology mapping observations. The inversion results have been used to provide the subsurface model for the safety analysis in rock engineering and we could assure the residents that the apartment has no problem in its safety after the completion of investigation works.

• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.1-8
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• 2005

Measurement of convergence was/is carried out manually throughout the world for tunnels under construction. However, manual method has certain limitations in terms of applicability for the tunnels in operation. This paper describes state of the art of convergence monitoring systems which are available for measuring displacement of existing tunnels. These technologies are analyzed as follows: 1 The Sofo system using the fiber optic sensors has been applied to the stress measurement of the tunnel lining. It has not yet been used for the monitoring of tunnel convergence because of its cost and reliability 2. A TPMS(Tunnel Profile Monitoring System) using tilt sensors and displacement sensors is used for the convergence monitoring of highway tunnels, subway tunnels and underground ducts. 3. A BCS(Bassett Convergence System) using a pair of tilt sensors can be used for the convergence monitoring of tunnels, however the accuracy of the measurement has to be improved because it uses AC input voltage during data acquisition. The system has to be validated before it can be applied to the tunnels in operation. Convergence monitoring systems using TPMS and/or BCS are recommended to be evaluated and improved by a series or tests in tunnels under construction in order to be applied to the main measuring section and the tunnels in operation.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.320-327
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• 2011

In this study, for stemming effect in blast of the mortar block body, the crushed granite sand as fine aggregate, which is waste rock obtained at the ○○ limestone mine, was investigated to compare with stemming materials such as sea sand, river sand, clayed soil and water can be acquired easily at the field. The mortar block body was manufactured with the dimensions of 50 cm width, 50 cm length and 70 cm height. The direct shear and sieve separator test were performed, and the properties of friction resistance were analyzed by the extrusion test for five stemming materials. Axial strain of steel bar and ejection velocity of stemming materials due to the explosive shock pressure in blasthole with the stemming length of 10 cm and 20 cm in the mortar blast test were measured by the dynamic data acquisition system. Among stemming materials, axial strain showed the largest value at the crushed granite sand as fine aggregate, and the ejection velocity was the smallest value at the stemming of water. The results has shown correlate with harden unit weight in blasthole, particle size distribution, shear resistance, and extrusion strength of stemming materials. The ejection velocity of stemming material at the mouth of blasthole and the axial strain of steel bar in the inside of blasthole tend to be inversely proportional to each other, represent exponentially.

• Journal of Conservation Science
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• v.20
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• pp.89-103
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• 2007

The bedrock beneath the Chokseongnu pavilion consists of sandstone with alternate dark-gray to light-brown siltstone and dark-gray shale of the Jinju Formation, where bedding is well developed toward the Chokseongmun gate. Large to small joints and overbreak from the erosion weathering have been developed in the bedrock. Besides, water leakage from development of discontinuity planes, fragmentation of shale, crack and joint by tree roots are observed on the bedrock. While shale and siltstone showed high sensitivity in physical and chemical weathering, respectively, sandstone indicated the highest weathering sensitivity in both. As the results of structural stability analysis, the whole bedrock has high instability in wedge failures, and especially section No. II slope is more instable than section No. I. Therefore, it is necessary for the bedrock to be strengthened by improvement method for soft foundations and the surface reinforcement. The trees causing mechanical collapse of the bedrock should be also removed and a water flow prevention measure or a water exhaust are required.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.2
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• pp.151-159
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• 2017

A deep geological disposal at a depth of 500 m in stable host rock is considered to be the safest method with current technologies for disposal of spent fuels classified as high-level radioactive waste. The most important requirement is that the temperature of the bentonite buffer, which is a component of the engineered barrier, should not exceed $100^{\circ}C$. In Korea, the amount of spent fuel generated by nuclear power generation, which accounts for about 30% of the total electricity, is continuously increasing and accumulating. Accordingly, the area required to dispose of it is also increasing. In this study, various duplex disposal concepts were derived for the purpose of improving the disposal efficiency by reducing the disposal area. Based on these concepts, thermal analyses were carried out to confirm whether the critical disposal system requirements were met, and the thermal stability of the disposal system was evaluated by analyzing the results. The results showed that upward 75 m or downward 75 m apart from the reference disposal system location of 500 m depth would qualify for the double layered disposal concept. The results of this study can be applied to the establishment of spent fuel management policy and the design of practical commercial disposal system. Detailed analyses with data of a real disposal site are necessary.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.21-33
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• 2015

This study tests the potential of detecting small-magnitude earthquakes (~M3.0) and their precursors using a long-term groundwater-monitoring database. In groundwater records from April to June 2012, abnormal changes in water level, temperature, and electrical conductivity were identified in the bedrock monitoring wells of the Gimcheon-Jijwa, Gangjin-Seongjeon, and Gongju-Jeongan stations. These anomalies could be attributed to the M3.1 earthquake that occurred in the Youngdeok area on May 30th, although no linear relationship was found between the scale of changes and the distance between each monitoring station and the epicenter, which is attributed in part to the wide screen design of the monitoring wells. Groundwater monitoring networks designed specifically for monitoring earthquake impacts could provide better information on the safety of underground space and on the security of emergency water-resources in earthquake disaster areas.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.233-244
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• 2017

We conducted hydraulic fracturing experiments on cement samples to investigate the dependency of fracture propagation on the viscosity of injection fluid and the in situ stress state. Ten cubic samples (20 cm side length) were produced using cement that was cured in water for more than one month. Samples were placed in a tri-axial compression apparatus with three independent principal stresses. An injection hole was drilled and the sample was hydraulically fractured under a constant injection rate. We measured injection pressures and acoustic emissions (AE) during the experiments, and investigated the fracture patterns produced by hydraulic fracturing. Breakdown pressures increased exponentially with increasing viscosity of the injection fluid. Fracture patterns were dependent on differential stress (i.e., the difference between the major and minor principal stresses). At low differential stress, multiple fractures oriented sub-parallel to the major principal stress axis propagated from the injection hole, and in some samples the fracture orientation changed during propagation. However, at high differential stress, a single fracture propagated parallel to the major principal stress axis. AE results show similar patterns. At low differential stress, AE source locations were more widespread than at high differential stress, consistent with the fracture pattern results. Our study suggests that hydraulic fracturing during shale gas extraction should be performed parallel to the orientation of minimum differential stress.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.1
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• pp.63-72
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• 2009

Recently the importance and interest for the microbes has been increased because several important results for the effects of microbes on the radioactive waste disposal have been published continuously. In this study, research status and major results on the various roles and effects of microbes in the radioactive waste disposal have been investigated. We investigated and summarized the roles and major results of microbes in a multi-barrier system consisting of an engineered barrier and a natural barrier which is considered in radioactive waste disposal systems. For the engineered barrier, we discussed about the effects of microbes on the corrosion of a waste container and investigated the survival possibility and roles of microbes in a compacted bentonite buffer. For the natural barrier, the roles of microbes present in groundwaters and rocks were discussed and summarized with major results from natural analogue studies. Furthermore, we investigated and summarized the roles and various interactions processes of microbes and their effects on the radionuclide migration and retardation including recent research status. Therefore, it is expected that the effects and roles of microbes on the radioactive waste disposal can be rigorously evaluated if further researches are carried out for a long-term behavior of the disposal system in the deep geological environments and for the effects of microbes on the radionuclide migration through geological media.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.526-535
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• 2006

An experimental study was carried out on a reduced scale tunnel model to grasp the behavioral feature of fire-induced smoke in the long tunnels. Based on Froude modeling, the 1/50 scaled tunnel model (20 m long) was constructed by acrylic tubes and paraffin gas was released inside the tunnel to simulate the 20 MW fire-induced smoke. me test results show, that after approximately 2 minutes of fire generation, was descended from the tunnel ceiling through the decrease of buoyancy, then it was symmetrically propagated about 90 meters for 4 minutes before jet fans were operated. The smoke was effectively controlled when the jet fans were operated and an air stream velocity was getting closed to reach a critical velocity (the minimum air velocity that requires to suppress the smoke spreading against the longitudinal ventilation flow during the tunnel fire situations). It was also found out that a range of smoke was spreaded about 3 meters from the origin of fire but the range was not propagated to the escape direction anymore. The early stage of the In operation, however, showed that the smoke was hardly controlled. It means that the operation of emergency ventilation system has many dangerous factors such as an intercepting breathing zone.

• Journal of the Mineralogical Society of Korea
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• v.20 no.3
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• pp.165-173
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• 2007

The KAERI Underground Research Tunnel (KURT) located in KAERI (Korea Atomic Energy Research Institute) was recently constructed following the site investigation in 2003. Its dimension is 180 m in length, 6 m in width, and 6 m in height, and it has a horseshoe-like cross-sec-lion and is located in the ground to the depth of 90 m. When the tunnel was dug into the ground with 100 m in length, fresh rocks, weathered rocks and fracture-filling materials were taken and examined by mineralogical and chemical analyses. There are phyllosilicate minerals such as illite, smectite and chlorite including calcite, which are filling some faults and cracks of the KURT rock. The illite and smectite usually coexist in the fracture, where their content ratio is different according to which mineral is predominant. There are high concentrations of U and Th in the rocks coated with iron-oxides and filled with secondary materials as compared with those in the fresh rocks. It seems that the radionuclides, which are slowly leached from the parent rocks or exist as a dissolved form in the groundwater and hydrothermal solution, may have been migrated along the fractures and thereafter selectively sorbed and coprecipitated on the iron-oxides and the fracture-filling materials. These results will be very useful far the evaluation of environmental factors affecting the nuclides migration and retardation when long-term safety is considered to the geological disposal of high-level radioactive wastes in the future.