• Tunnel and Underground Space
• /
• v.18 no.3
• /
• pp.165-174
• /
• 2008

Thermo-hydro-chemico-mechanical evolution of the radioactive waste repository and surrounding geological media is one of the key issues for the radioactive waste disposal. This article describes not only the basic context for the site selection but also a reasonable strategy for the repository related research based on the results of the French repository project carried out by ANDRA (National radioactive waste management agency). To have some alternatives for the determination of a preferable depth and geological media, it would be recommendable to establish a database system. The curing process of the fractures or microfissures in the EDZ (Excavation Disturbed Zone) during operation time has to be examined considering the evolution of the EDZ and the reversibility of the repository. It is prerequisite to carry out a feasibility study and to validate the design concept and design parameters in a properly constructed underground research laboratory (URL) in Korea.

• The Journal of Engineering Geology
• /
• v.23 no.1
• /
• pp.47-55
• /
• 2013

To analyze lateral displacement of excavation walls exposed during the construction of Subway Line 1 in the Daegu region, inclinometer measurement data for sites D4, D5, and Y6 are investigated from the perspective of engineering geology. The study area, in the Banyawol Formation, Hayang Group, Gyeongsang Supergroup, is in the lower part of bedrock of andesitic volcanics, calcareous shale, sandstone, hornfels, and felsite dykes that are unconformably overlain by soil. The rock mass around the D4 site is classified as RMR-V grade and the maximum lateral displacement of 101.39 mm, toward N34W, was measured at a bedding-parallel fault, at a depth of 12 m. The rock mass around the D5 site is classified as RMR-IV grade and the maximum lateral displacement of 55.17 mm, toward the south, was measured at a lithologic contact between shale and felsite, at a depth of 14 m. The rock mass around the Y6 site is classified as RMR-III grade and the maximum lateral displacement of 12.65 mm, toward S52W, was measured at an unconformity between the soil and underlying bedrocks, at a depth of 7 m. The directions of lateral displacement in the excavation walls are vector sums of the directions perpendicular to the excavation wall and horizontally parallel to the excavation wall. Lateral displacement graphs according to depth in the soil profile show curvilinear trajectories, whereas those in bedrock show straight and rapid-displacement trajectories.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.6 no.4
• /
• pp.327-343
• /
• 2004

During tunnel construction, ground failures often occur due to existence of weak zones, such as faults, joints, and cavities, ahead of tunnel face. It is hard to detect effectively weak zones, which can lead underground structure to fail after excavation and before supporting, by using conventional characterization methods. In this study, an enhanced analytical method of predicting weak zones ahead of tunnel face is developed to overcome some problems in the conventional geophysical exploration methods. The analytical method is based on Coulomb's and Gauss' laws with considering the characteristics of electric fields subjected to rock mass. Using the developed method, closed form solutions are obtained to detect a spherical shaped zone and an oriented fault ahead of tunnel face respectively. The analytical results suggest that the presence of weak zones and their sizes, location, and states can be accurately predicted by combining a proper inversion process with resistance measured from several electrodes on the tunnel face. It appears that the skin depth or resistivity in rock mass is affected by the diameter of tunnel face, natural electric potential and noises induced by experimental measurement and spatial distribution of uncertain properties. The developed analytical solution is verified through experimental tests. About 1800 concrete blocks of 5cm by 5cm by 5cm in size are prepared and used to model a joint rock mass around tunnel face. Weak zones are simulated ahead of tunnel face with a material which has relatively higher conductivity than concrete blocks. Experimental results on the model test show a good agreement with analytical results.

• Journal of the Korean GEO-environmental Society
• /
• v.19 no.12
• /
• pp.25-32
• /
• 2018

This paper investigates the effect of rock discontinuities on a shear stress wave that is induced by earthquake or blasting and provides the result of numerical parametric studies. The numerical tests of different conditions of rock and discontinuity have been carried out after confirming that the numerical approach is valid throughout a verification analysis from which the test results were compared with a theoretical solution. In-situ stress condition was considered as a rock condition and internal friction angle and cohesive value, which are the shear strength parameters, were considered as discontinuities condition. The joint inclination angle was also taken into account as a parameter. With the various conditions of different parameters, the test results showed that a shear stress wave propagating through a mass is highly influenced by the shear strength of discontinuities and the condition of joint inclination angle as well as in-situ stress. The study results indicate that when earthquake or blasting-induced dynamic loading propagates through a jointed rock mass or a stratified soil ground the effect of in-situ stress and discontinuities including a stratum boundary should be taken into account when evaluating the dynamic effect on nearby facilities and structures.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.5 no.2
• /
• pp.113-122
• /
• 2007

In this study, uranium migration experiments have been performed using a natural groundwater and a granite core with natural fractures in a glove-box constructed to simulate an appropriate subsurface environment. Groundwater flow experiments using the non-sorbing anionic tracer Br were carried out to analyze the flow properties of groundwater through the fracture of the granite core. The result of the uranium migration experiment showed a breakthrough curve similar to that of the non-sorting Br. This result may imply that uranium migrates as anionic complexes through the rock fracture since uranium can form carbonate complexes at a given groundwater condition. The distribution coefficient $K_d$ of the uranium between the groundwater and the fracture filling material was obtained as low as 2.7 mL/g from a batch sorption experiment. This result agrees well with the result from the migration experiment, showing a faster elution of the uranium through the rock fracture. In order to analyze retardation properties of the uranium through the rock fracture, the retardation factor $R_d({\sim}16.2)$ was obtained by using the $K_d$ obtained from the batch sorption experiment and it was compared with the $R_d({\sim}14.3)$ obtained by using the result from the uranium migration experiment. The values obtained from the both experiments were very similar to each other. This reveals that the retardation of the uranium is mainly occurred by the fracture filling material when the uranium migrates through the fracture of a granite core.

• Food Science and Preservation
• /
• v.21 no.5
• /
• pp.688-693
• /
• 2014

The quality and sensory characteristics of tofu were investigated with various levels of black garlic extract (BE) added to it in 0, 1, 3, 5 and 7%-weight soymilk, before it was coagulated with $MgCl_2$ (MC, BEM-A, BEM-B, BEM-C and BEM-D) and concentrated to $8^{\circ}Brix$ deep ground sea-like water (SC, BES-A, BES-B, BES-C and BES-D). The overall acceptability of the tofu samples was higher (SC > BES-A > BEM-A) than that of the other samples. The addition of BE was influenced by the color, flavor and taste of the tofu, and the more BE was added, the tougher the tofu became. The tofu yield with various amounts of black garlic extract did not significantly differ among the samples. The pH range was 5.61~6.15 and decreased as more BE was added, whereas the turbidity increased. Also, the L value of the tofu decreased as more BE was added. The a value showed a tendency opposite that of the L value. The b value did not significantly differ among the samples. The texture profile analysis of the tofus showed that the hardness, chewiness, and gumminess significantly increased as more BE was added. In conclusion, it was found that the addition of 1% BE will improve the quality and sensory characteristics of tofu.

• Tunnel and Underground Space
• /
• v.17 no.3 s.68
• /
• pp.203-215
• /
• 2007

Stability and mechanical deformation behavior of rock masses are highly dependent on the mechanical characteristics of contained discontinuities. Therefore, mechanical characteristics of the discontinuities should be considered in the design of tunnel and underground structures. In this study, direct shear tests for rough granite joints were carried out under constant normal stiffness conditions. Effects of initial normal stress, shear velocity, and surface roughness on the characteristics of shear strength and deformation behaviors were examined. Results of shear testing under constant normal stiffness conditions reveal that shear behaviors could be classified into two categories, based on the amount of decrease in shear stress at the Int peak shear stress. With initial normal stiffness increasing, it turned out that shear displacement at peak stress and the first peak shear stress increased, however friction angle and friction coefficient showed decrease. In case of shear stiffness and average friction coefficient, it turned out that they are not dependent on the initial normal stress. Minor effects of shear velocity on rough joints were observed in several shear quantities. However, the effects of shear velocity were insignificant regardless of the normal stress increase. Change of shear strength and deformation characteristics on joint roughness were examined, however, it turned out that the variations were attributed to deviation of shear test specimens.

• The Journal of Engineering Geology
• /
• v.29 no.1
• /
• pp.1-12
• /
• 2019

Earthquake can change underground stress condition around the hypocenter and affect the fracture systems of the rocks. In Korea, the M5.8 Gyeongju earthquake on September 12, 2016 and M5.4 Pohang earthquake on November 15, 2017 occurred inside the Yangsan fault zone and possibly affected the fracture systems in the Yangsan fault zone and nearby rock masses. In this study, the characteristics of the fracture system (fracture orientation, number of the fractures, fracture spacing and aperture, dip angle, fracture density along depth, and relative rock strength) of the rocks in the low/intermediate level radioactive waste repository site located in the coastal area of the East Sea are analyzed by the impact of the Gyeongju and Pohang earthquakes using acoustic televiewer data taken from the boreholes at the radioactive waste repository site in 2005 and 2018. As a result of acoustic televiewer logging analysis, the fracture numbers, fracture aperture, and fracture density along depth overall increased in 2018 comparing to those in 2005. This increase tendency may be due to changes in the fracture system due to the impact of the earthquakes, or due to weathering of the wall of the boreholes for a long period longer than 10 years after the installation of the boreholes in 2005. In the borehole KB-14, on the whole, the orientation of the fractures and the average fracture spacing are slightly different between 2005 and 2018, while dip angle and relative rock strength in 2005 and 2018 are similar each other.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.6C
• /
• pp.407-419
• /
• 2006

Situations where support is provided solely in shaft resistance of drilled shafts are where the base of the drilled hole cannot be cleaned so that it is uncertain that any end bearing support will be developed. Alternatively, where sound bed rock underlies low strength overburden material, it may be possible to achieve the required support in end bearing on the rock only, and assume that no support is developed in the overburden. However, where the drilled shaft is drilled some depth into sound rock, a combination of side wall resistance and end bearing can be assumed. Both theoretical and field studies of the performance of rock socketed drilled shafts show that the major portion of applied load is usually carried in side wall resistance. Normal stress at the rock-concrete interface is induced by two mechanisms. First, application of a compressive load on the top of the pile results in elastic dilation of the concrete, and second, shear displacement at the rough surface of the drilled hole results in mechanical dilation of the interface. If the stiffness of the material surrounding the socket with respect to normal displacement is constant, then the normal stress will increase with increasing applied load, and there will be a corresponding increase in the shear strength. In this study, the numerical analyses are carried out to investigate the behavioral characteristics of side of rock socketed drilled shafts. The cause of non-linear head load-settlement relationship and failure mechanism at side are also investigated properly and the design charts are suggested and verified for the leading to greater efficiency and reliability in the pile design.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.4
• /
• pp.21-32
• /
• 2002

Small and full scale model tests were performed to obtain the transient responses of shafts subjected to elastic impact by impact-echo test. Four end conditions of drilled shafts were considered: (1) free, (2) fixed, (3) rock-socketed, and (4) soft bottom. In small scale model tests, mock-up shafts were fabricated to simulate these four drilled shafts using poly-urethane and plastic material. Additionally, skin frictions between shaft and rock were changed to find out the effect of side contact on dynamic responses. All impact responses were tested in the air. Subsequently, full scale model tests were also carried out on concrete shafts that were in free and rock-socketed condition. The end conditions of the drilled shafts could be identified with good reliability by the waveforms from both small and full scale model tests. The results obtained in this study will provide an improved understanding of the impact responses for end conditions, especially for rock-socketed drilled shafts that are frequently designed and built in Korea.