• Tunnel and Underground Space
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• v.7 no.2
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• pp.130-135
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• 1997

When crystalline rocks are heated, thermal stress is induced by the differences in thermal expansion of the mineral composition and its orientation. In this study, high temperature uniaxial compressive tests were carried out for Iksan and Hwangdeung granites to study the deformation and failure behavior due to thermal loading. Compressive and tensile strength of Hwangdeung granite for 20$0^{\circ}C$ decreased to 80% and 82% of the room temperature strength, and those of Iksan granite decreased to 90% and 92% for 20$0^{\circ}C$, respectively. Elastic moduli of both granites were decreased sharply at the stress level of 80% of ultimate failure strength. Elastic moduli of both granites by variation of temperature at 50% of ultimate failure strength was decreased as almost linearly.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.91-99
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• 1997

To stabilize the energy price, the more storage facilities of energy are required and among the storage methods of LPG and LNG, the method of storage at low temperature under normal confining pressure is considered. It is needed to understand the mechanical and thermal characteristics of rock under temperature variation so that the behaviors of rock can be predicted. In this paper, the variation of the rock charateristics of the Hwangdeung granite and the Boryung sandstone is studied at low temperature. The mechanical characteristics of rock under low temperatures are that as temperature decreased, unaxial compression strength and Young's modulus increased for Hwangdeung granite; strength and Young's modulus in wet condition were greater than those in dry condition. In the case of Boryung sandstone, as temperature decreases unaxial compression strength and Young's modulus increase but decrease below -10$0^{\circ}C$ in dry condition and below -16$0^{\circ}C$ in wet condtion. The mechanical characteristics of rock after cooling to previous temperature and thawing are that uniaxial compression strength and Young's modulus decrease as temperature decreases. Uniaxial compression strength and Young's modulus in wet conditon decrease more than those in dry condition. Brazilian tension strength decreases as temperature decreases.

• Explosives and Blasting
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• v.23 no.4
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• pp.31-44
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• 2005

In highly stressed conditions, the excavation damage zone induced by stress redistribution and disturbance must be evaluated after tunnel excavation. Therefore, the investigation of stress-induced deformation and fracture in rock is indispensable. In this study, fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by the moving point regression technique as well as acoustic emission measured during uniaxial compression tests. Especially, the modified procedures to determine damage thresholds more systematically were newly proposed, and successfully applied to rock. From experiments, crack initiation and track damage stress levels were estimated to be $33{\~}36\%$ and $84{\~}89\%$ of uniaxial compressive strength respectively, for both of Hwangdeung granite and Yeosan marble. However, the normalized crack closure stress level for Yeosan marble was much higher than for Hwangdeung granite. In addition, the largest proportion of total axial strain in Hwangdeung granite was attributable to elastic deformation and initial microcracking. However, the greatest part of axial deformation in Yeosan marble arose from initial crack closure and unstable cracking. Finally, it was seen that unstable cracking after the crack damage stress level played a key part in the lateral deformation in rocks under uniaxial compression.

• The Journal of Engineering Geology
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• v.34 no.1
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• pp.137-146
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• 2024

The pertinent Korean Industrial Standard (KS F) requires that rocks dried at 105 ± 5℃ be taken out of the oven into air and weighed on a scale. However, when rocks are exposed to air after the drying process, they absorb moisture, meaning that their weight will increase. In this study, eight cubic samples of Hwangdeung granite of different sizes were used to measure and compare the dry weight. The dry singularity weight measured in air was smaller than that measured in the drying oven. The difference in dry weight showed a positive correlation with sample size. Conversely, the difference in dry weight per unit weight of rock showed a negative correlation with sample size. The weight of a rock sample exposed to air is determined by the magnitude of the influence of convection currents occurring around the heated rock and the influence of moisture absorption in air. A singularity occurs when the magnitudes of these two effects are equal. The larger the rock sample, the longer the time taken for the singularity to occur, the greater the weight loss of the sample, and the longer the time taken for the sample to return to the initially measured weight on account of the greater moisture absorption for larger samples than smaller samples. In the future, research into the singularity and dry weights measured inside the drying oven will help to identify and address the limitations of the current KS F testing regulations.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.89-100
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• 2010

Although various methods for determination of damage threshold in rock have been suggested, clear damage thresholds were determined by some methods, but different thresholds were measured by other methods. We determined the damage thresholds in Hangdeung granite using all the methods suggested, and investigated the best methods, applicability and errors of each method. The crack initiation threshold and the crack damage threshold which are important in investigation of characteristics of crack development and failure were verified by field strength ratio method and long-term constant load test. The crack closure stress and the crack initiation stress were 57.5 MPa and 77.6 MPa, and the most exact values were yielded by crack volumetric strain. The secondary crack initiation stress was 90.6 MPa and AE event count and AE event count rate were the effective methods. The volumetric stiffness, AE event count and AE event count rate were the most effective methods for determination of crack coalescence threshold and crack coalescence stress was 110.3 MPa. The crack damage stress was 127.5 MPa and was measured correctly by volumetric stiffness and AE event count rate. The ratio between crack initiation stress and uniaxial compressive strength was 0.47 which was very similar with the FSR value of 0.46. The ratio between crack damage stress and uniaxial compressive strength was almost the same as the ratio between long-term strength and uniaxial compressive strength, indicating that the crack initiation stress and the crack damage stress measured were correct.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.81-90
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• 2008

It is of great importance to determine the optimum cutter spacing in TBM. In order to determine the optimum cutter spacing, a series of cutting tests by linear cutting machine (LCM) are performed with changing cutter space. This study showed that a numerical method for estimating the optimum cutter spacing could be developed by AUTODYN-3D in order to overcome the limitation of LCM test. By using this method, the optimum cutter spacing of Hwangdeung granite was estimated.

• Journal of Conservation Science
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• v.27 no.2
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• pp.211-222
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• 2011

The Mireuksaji stone pagoda was built foundation in the reign of King Moo (AD 639) in the Baekje Kingdom of ancient Korea. The stone properties of the pagoda were quarried from Mountain Mireuk, which are medium to coarse-grained light gray biotite granite formed during the Jurassic, and are composed of quartz, feldspar, biotite, muscovite, apatite and allanite. It was strong relatively but became weak from prolonged weathering, and as a result its durability fell to $883kgf/cm^3$ (moderate weathering degree). In the process, cut-off (31%), deletion (57%) and crack (44%) occurred in foundation materials by the influence of bending, shear and compressive force. Hereat, the original materials were treated through a preservation process. As a result, approximately 74% of original materials have been able to be reused, inclusive of 55 materials that were to be partially replaced by new stones. On the other hand, it is inevitable that the other 26% including exterior stones and support-based stones have to be partially replaced by new stones. It implies that there is a need to find stones that are identical or similar to those of the pagoda. Consequently, a lithological study was conducted on stones in quarries located in Iksan and an investigation was made into their properties. The results showed that stones in the Hwangdeung area were most similar to those of the pagoda mineralogically and their properties were most stable.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.350-363
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• 1999

The precision cyclic shear test system was established to investigate the mechanical characteristics of rough rock joints under cyclic loading conditions. Laboratory cyclic shear tests were conducted for saw-cut joints and artificial rough rock joints using Hwangdeung granite and Yeosan marble. Surface roughness and aperture characteristics of specimens were examined by measuring surface topography using the laser profilometer. Peak shear strength, phase difference during loading and unloading, and anisotropic shear behavior were investigated throughout the cyclic shear test results. These features and their subsequent variations in each loading cycle are significantly dependent upon the second order asperities and the strength of intact rock. It was observed that degradation of asperities for rough rock joints under cyclic shear loading followed the exponential degradation laws of asperity angle and that the mechanism for asperity degradation would be different depending upon the normal stress level, roughness of joint surface and the loading stage.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.345-356
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• 2013

Numerical simulation on rock cutting by a TBM disc cutter was carried out using SPH (Smoothed Particle Hydrodynamics) code. AUTODYN3D, a commercial software program based on finite element method, was used in this study. The three-dimensional geometry of a disc cutter and a rock specimen were modeled by Lagrange and SPH code respectively. The numerical simulation was carried out for Hwangdeung granite for 10 different cutting conditions. The results of the numerical simulation, i.e. the relation between cutter force and failure behavior, had a good agreement with those from LCM test. The cutter forces measured in the numerical simulation had 10% deviation from the LCM test results. Moreover, the optimum cutter spacing was almost identical with the experimental results. These results indicate that SPH code can be successfully used had applicability for simulation on rock cutting by a TBM disc cutter. However, further study on Lagrange-SPH coupled modelling would be necessary to reduce the computation time.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.559-572
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• 2020

This paper performs laboratory experiments for borehole stability considering temperature and true triaxial stress condition, and observes a thermo-mechanical behavior of the rock under stress and temperature conditions of deep underground. China yellow sandstone and Hwangdeung granite specimens were used to perform a true triaxial compression test. Mechanical tests were carried out under nine confining pressure conditions, and thermo-mechanical tests using granite samples were carried out under six confining pressure conditions at 60-100℃. In the mechanical tests, maximum principal stress at borehole breakout was proportional to intermediate principal stress. In the thermo-mechanical tests, it was confirmed that thermal stress is added to the stress field of the borehole with the increase in temperature, resulting in additional breakout progress. To analyze the results of the laboratory experiment, Mogi-Coulomb failure criterion was used. The results of traditional triaxial compression test on cylindrical specimens and borehole breakout under true triaxial compressions matched well with Mogi-Coulomb failure criterion.