• Tunnel and Underground Space
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• v.29 no.3
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• pp.157-171
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• 2019

The fracturing by liquid carbon dioxide ($LCO_2$) as a fracking fluid has been an alternative to mitigate the environmental issues often caused by the conventional hydraulic fracking since it facilitates the fluid permeation owing to its low viscosity. This study presents how $LCO_2$ injection influences the breakdown pressure, acoustic emission, and fracture morphology. Three fracturing fluids such as $LCO_2$, water, and oil are injected with different pressurization rate to the synthetic and porous mortar specimens. Also, the shale which has been a major target formation in conventional fracking practices is also tested to examine the failure characteristics. The results show that $LCO_2$ injection induces more tortuous and undulated fractures, and particularly the larger fractures are developed in cases of shale specimen. On the other hand, the relationship between the fracturing fluids and the breakdown pressure shows opposite tendency in the tests of mortar and shale specimens.

• Explosives and Blasting
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• v.26 no.1
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• pp.57-66
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• 2008

It has been proven that the pre-cracking notches in a blasting hole are applicable to control crack growth along specific direction. This study compared the roughnesses of the fracture plane resulting from test blasts using a regular charge hole and notched charge hole to investigate the effect of the notches of charge hole on the formation of fracture plane. A notch bit system was used to drill the notched hole in the rock specimens. The surfaces of the fracture planes were reconstructed as Digital Elevation Model (DEM) using digital photogrammetric method and the roughnesses of the surfaces were estimated with Surface Roughness Profile Index (SRp).

• Tunnel and Underground Space
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• v.20 no.3
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• pp.217-224
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• 2010

Three relatively homogeneous granitic rocks were studied to investigate the relationship between their microstructural properties and fracture toughness. Fracture toughness and ultrasonic velocity were varied with the orientation of mineral's long axis and microcrack, obtained from optical microscope. The lowest fracture toughness values are obtained, when the fracture propagates parallel to weakness planes which have the orientation of mineral's long axis and microcrack, in other words, when weakness planes develop perpendicular to the direction of tensile stress agrees with that of rift plane. The fracture toughness values, measured with the short rod method, varied from 1.63 to 2.62 MPa $m^{0.5}$, and their values are related with the average grain size and average microcrack length.

• The Journal of Engineering Geology
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• v.16 no.2 s.48
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• pp.179-187
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• 2006

Two specimens of mortar containing artificial slit and Geochang granite containing the straight notch were selected to be used in this research. Source mechanism of micro-crack by radiation pattern based on dislocation the-ory was estimated by the first motion of longitudinal wave and spatial distribution between the location of transducers for monitoring acoustic emission and source coordinates determined by the application of the least square method. Result of analysis showed that the orientation of dislocation surfaces due to shear dislocation and tensile dislocation squares considerably with crack direction visually observed. The ultimate goal of this study is to provide fundamental information for source mechanism of micro-crack within materials.

• Nuclear Engineering and Technology
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• v.24 no.1
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• pp.98-109
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• 1992

In this study uniaxial cyclic loading tests were performed on Cheon-Ho Mt. Limestone specimens to investigate the fatigue failure behavior. The loading rate was kept constantly at 760kg/$\textrm{cm}^2$/sec under cyclic loading. In order to reveal the fatigue behavior for each rock type, the test results were mutually compared with previous studies carried out on Indiana Limes-tone and Seong-Ju Sandstone. Fatigue data is presented in the form of S-N curves, which illustrate the relationship of maximum applied stress(S) to the number of cycles(N) required to produce failure. For the purpose of comparing the S-N curves for each rock type, the test data were formulated up to 10$^4$cycles and the correlation coefficients(R) on Cheon-Ho Mt. Limestone and Seong-Ju Sandstone specimen are 0.886 and 0.983, respectively. All three rock specimens were found to have shorter fatigue life at higher applied stress levels. The fatigue life for each rock type was considered as no less than 81.5, 70 and 74.8%, for Cheon-Ho Mt. Limestone, Indiana Limestone and Seong-Ju Sandstone, respectively. The comparison in static strength for monotonic loaded specimens and specimens which did not fail even after 10$^4$cycles indicated that the increasing rate of strength was about 6.18 and 10.96% , for Cheon-Ho Mt. Limestone and Indiana Limestone, respectively. Poisson's ratio and volumetric strain for Cheon-Ho Mt. Limestone and Seong-ju Sandstone, tended in all the cases to rapidly increase at higher stress levels and with an increase in number of cycles. This increasing trend becomes rapid and obvious just before failure. Also Poisson's ratio and volumetric strain for each stress level were compared and analyzed at the first cycle and the cycle prior to failure.

• Journal of Conservation Science
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• v.21
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• pp.33-40
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• 2007

The consolidation application of SILRES BS OH 100 was investigated, which has been used for consolidation of the weathered shale. The liquid SILRES BS OH 100 was polymerized by the sol-gel reaction with air moisture, and the XRD patterns showed that the gel was an amorphous solid. The drastic weight reduction of the sample was found by differential thermal analysis, which was followed to the formation of $Si(OH)_4$ particles. After consolidation, the polymerized gel was filled into the voids within the shale. The capillary water absorption of the consolidated shale was reduced to 48.7%, and the abrasive strength was improved.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.53-58
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• 2014

The uniaxial compressive strength and Young's modulus of intact rocks are the most important analytical parameters for design of rock mass structures. But the preparation of the samples for uniaxial compressive test is a hard and time consuming task. By using ultrasonic test, engineers can predict the analytical parameters that is the uniaxial compressive strength and Young's modulus. The uniaxial compressive test and ultrasonic test were carried out 115 samples of igneous rocks, 74 samples of metamorphic rocks and 55 samples of sedimentary rocks and, after regression analysis of the test results, best fit equations for predicting the uniaxial compressive strength and Young's modulus are proposed. In order to obtain a better correlations coefficient between uniaxial compressive strength and P-wave velocity, the P-wave velocity were multiplied by density values. The proposed equations for predicting uniaxial compressive strength and Young's modulus using ultrasonic test provide reliable results.

• Economic and Environmental Geology
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• v.44 no.2
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• pp.171-180
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• 2011

For 21 rock samples consisting of granite, sandstone and the effective thermal conductivity (TC) was measured with the LFA-447 Nanoflash, and mineralogical compositions were also determined from XRD analysis. The structural models were used to examine the effects of quartz content and the size of minerals on TC of rocks. The experimental results showed that TC of rocks was strongly related to quartz content with $R^2$ value of 0.75. Therefore, the proposed regression model can be a useful tool for an approximate estimation of TC only from quartz content. Some samples with similar values of quartz content, however, illustrated great differences in TC, presumably caused by differences in the size of minerals. An analysis from structural models showed that TC of rocks with fine-grained minerals was likely to fall in the region between Series and EMT model, and it moved up to ME and Parallel model as the size of minerals increased. This progressive change of structural models implies that change of TC depending on the size of minerals is possibly related to the scale of experiments; TC was measured from a disk sample with a thickness of 3 mm. Therefore, in case of measurements with a thin sample, TC can be overestimated as compared to the real value in the field scale. The experimental data illustrated that the scale effect was more pronounced for rocks with bigger size of minerals. Thus, it is worthwhile to remember that using a measured TC as a representative value for the real field can be misleading when applied to many geothermal problems.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.337-348
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• 2005

Jurassic granite from Pocheon area were tested to investigate the effect of microcracks on mechanical properties of the granite. Three oriented core specimens were used for uniaxial compressive tests and each core specimen are perpendicular to the axes'R'(rift plane),'c'(grain plane) and'H'(hardway plane), respectively Among vacious elastic constants, the variation of Poisson's ratio as function of the directions was examined. From the related chart between ratio of failure strength and Poisson's ratio, H-specimen shows the highest range in Poisson's ratio and Poisson's ratio decreases in the order of C-specimen and R-specimen. The curve pattern is nearly linear in stage $I\simIII$ but the slope increases abruptly in stage H-3. As shown in the related chart, diverging point of a curve is formed when ratio of failure strength is $0.92\sim0.96$ Stage IV -3 is out of elastic region. The behaviour of rock in the four fracturing stages was analyzed in term of the stress-volumetric strain me. From the stress increment-volumetric strain equations governing the behaviour of rock, characteristic material constants, a, n, Q, m and $\varepsilon_v^{mcf}$, were determined. Among these, inherent microcrack porosity$(a, 10^{-3})$ and compaction exponent(n) in the microcrack closure region(stage I ) show an order of $a^R(3.82)>a^G(3.38)>a^H(2.32)\;and\;n^R(3.69)>n^G(2.79)>n^H(1.99)4, respectively. Especially, critical volumetric microcrack strain($\varepsilon_v^{mcf}$) in the stage W is highest in the H-specimen, normal to the hardway plane. These results indicate a strong correlation between two major sets of microcracks and mechanical properties such as Poisson's ratio and material constants. Correlation of strength anisotropy with microcrack orientation can have important application in rock fracture studies.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.251-262
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• 2014

Inorganic binders were studied in order to apply a conservation material for stone monument. A pure inorganic binder and 3 species of inorganic binder which contain additives on the basis of a pure inorganic binder were selected as test samples. Through the application of inorganic binders on Geochang granite investigate their influences on stone. pH 4.0 and 5.6 acid solution, respectively were manufactured on the basis of the acidity of domestic rainfall. Alkaline water with pH 8.0 and deionized water with pH 6.85 were prepared as control group. Changes in weights of inorganic binders were not definite according to the acidity of water while weight losses in inorganic binder type were greater after reaction with the water. The compressive strengths of pure inorganic binder was largest before the test but its decrease rate were larger after reaction with the water. Water absorption rate of inorganic binders are 6.72 to $12.44kg/m^2{\cdot}t^{1/2}$ after reaction with the water. Such high absorption was considered that it forced water to move deep into inorganic binder and made the components of inorganic binder dissolve. Acidities of the water of pH 4.0, 5.6, 6.85 and 8.0, respectively were changed to pH 9.0-10.0 after reaction with the inorganic binders. Ion concentrations in the water changed after reaction with the inorganic binders and $Mg^{2+}$, and $K^+$ significantly increased, dissolved from the binder. The high concentration of ions detected showed that the binder reacted with water and formed white salts with high solubility such as $MgSO_4{\cdot}nH_2O$, $KNO_3$. Ion concentrations significantly decreased from the binder after treatment with consolidant and water repellent.