• Tunnel and Underground Space
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• v.32 no.6
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• pp.530-548
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• 2022

The site selection process for deep geological disposal of high-level radioactive waste will be conducted in stages, and 103 evaluation parameters related to site selection have been proposed. In the field of rock mechanics and rock engineering, there are 33 evaluation parameters for intact rock, joint and rock mass, and they are applied in the basic and detailed investigation stages. In this report, uniaxial compressive strength, in-situ stress, joint distribution, and rock mass classification were selected as the main evaluation parameters, and among them, uniaxial compressive strength and in situ stress were selected as key evaluation parameters. Statistical techniques or regression analysis were performed for granite in Wonju and Chuncheon to evaluate the distribution range for the selected key evaluation parameters. The average of the uniaxial compressive strength in the Wonju area estimated through the posterior distribution is about 171 MPa, and about 123 MPa in the Chuncheon area. The maximum in situ stress acting in the Wonju area was less than 30 MPa and less than 40 MPa in the Chuncheon area. The direction of the maximum horizontal stress calculated by regression analysis was 101° in Wonju, and in the case of Chuncheon, it was 95°, respectiviely.

• 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.

• Journal of The Geomorphological Association of Korea
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• v.18 no.3
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• pp.21-36
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• 2011

Rock Weathering is a basic of geomorphological evolution as a preparation of materials. Of those, frost shattering has traditionally been considered as the operative process causing rock breakdown in cold regions as well as temperate zone. Each Granite(fresh rock, semi-weathered), Gneiss, Limestone, Dolomite was prepared slab specimens in ten, repeated freeze-thaw cycles of 180 under the -25℃~+30℃, and the changes was observed in physical properties and weathering aspect. Rock shattering was more active in waterlogging conditions rather than atmospheric and soil conditions. Limestone and Dolomite that high porosity are most severely crushed. Gneiss, regardless surface of the crack, joint, fissure and has a lowest rock strength(SHV), was even though no physical changes and their weathering product do not generate, has a very high resistance to weathering.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.156-161
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• 2003

Mechanical behavior of rock joints usually can be characterized by small-scale laboratory shear tests due to economical and technical limitations, but their applicability to the behaviour of rock mass has been always questioned by a number of researchers because of scale effect. Though there have been several researches regarding the scale effect, it has been a controversial problem how to apply the result of small-scale laboratory shear test directly to field design from different conclusions among researchers. In order to grasp the trend of scale effect of shear behavior, a series of direct shear tests on replicas of natural rock joint surfaces made of gypsum cement with different size and roughness were conducted and analyzed. Result showed that as the size of the specimen increased, average peak shear displacement increased, but average shear stiffness and average peak dilation angle decreased. As for the dependency of scale on shear strength, the degree of scale effect was dependent on normal stress and roughness of rock joint. For the condition of low normal stress and high roughness, decrease of average peak shear strength with increasing size of joint was evident.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.146-155
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• 2006

The target slope of this study, formed during the construction of highway, is the very high infinite slope where sliding began along the discontinuity. Although an attempt was made to stabilize the upper part of the slope by installing the rock anchors, large scale failure was occurred at the lower part if the reinforced area. Afterwards, subsequent failures were observed two times. To investigate the cause of the failure, residual shear strength was measured by performing the direct shear test of rock specimen of the site. The anchor design was based on the pull-out test. Considering the slope surface where the undulation was severe and the variation of strength was very large, buttressing was used to obtain the required anchoring capacity.

• Journal of the Korean GEO-environmental Society
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• v.23 no.8
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• pp.23-28
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• 2022

In Korea, 70% of the land is mountainous and structures occupy a high proportion in railway and road construction. In particular, in recent years, the construction of high-speed railways and highways for high-speed driving is rapidly increasing. At the same time, the construction of tunnels is also increasing. The number of tunnel construction cases in which long-term deformation occurs after tunnel excavation is completed is increasing. The stability of these tunnel structures depends entirely on the characteristics of the rock surrounding the tunnel excavation. In the case of pyroclastic rock, which is the subject of this study, it is generally vulnerable to weathering and has a characteristic that its strength decreases over a long period of time. Tunnel design and construction planning considering the strength characteristics of pyroclastic rocks are essential. This study analyzed the cases of over-deformation that occurred at the tunnel site in the pyroclastic section. Based on this study, a plan for tunnel design and construction management in an area where pyroclastic rock exist in the future is presented.

• Smart Structures and Systems
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• v.29 no.4
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• pp.535-547
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• 2022

Failure patterns of rock specimens represent valuable information about the mechanical properties and crack evolution mechanism of rock. Several kinds of research have been conducted regarding the failure mechanism of brittle material, however; the influence of brittleness on the failure mechanism of rock specimens has not been precisely considered. In the present study, experimental and numerical examinations have been made to evaluate the physical and mechanical phenomena associated with rock failure mechanisms through the uniaxial compression test. In the experimental part, Unconfined Compressive Strength (UCS) tests equipped with Acoustic Emission (AE) have been conducted on rock samples with three different brittleness. Then, the numerical models have been calibrated based on experimental test results for further investigation and comparing the micro-cracking process in experimental and numerical models. It can be perceived that the failure mode of specimens with high brittleness is tensile axial splitting, based on the experimental evidence of rock specimens with different brittleness. Also, the crack growth mechanism of the rock specimens with various brittleness using discrete element modeling in the numerical part suggested that the specimens with more brittleness contain more tensile fracture during the loading sequences.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.825-835
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• 2019

When the tunnel is designed, the ground is classified into several grades and the corresponding support system is applied according to the support pattern table. However, a simple pattern application based on rock grade does not take into account the longitudinal stress transitions occurring at rock grade boundaries. In this study, three-dimensional numerical analysis was performed to estimate the stress change in the longitudinal rock grade change of NATM tunnel, and the influence zone of load transfer was investigated using the influence line and trend line. As a result, the downward change of rock grade in the direction of tunnel excavation occurs in the range of 0.35~0.7D from low-strength rock to high-strength rock around the grade change boundary. It is necessary to apply a downward pattern of about 1.0D to the safety direction in consideration of the influence range of 0.35D to 0.7D.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.304-317
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• 2009

Most crystalline rocks have much higher compressive strength than tensile strength and show brittle failure. In-situ rock mass, strong enough in general sense, often fails in brittle manner when subjected to high stress exceeding strength in due of geometrically induced stress concentration or of high initial stress. Therefore, it is necessary to verify the brittle failure characteristics of rock and rock mass for proper stability assessment of underground structures excavated in great depths. In this study, damage controlled tests were conducted on biotite-granite and granitic gneiss, which are the two major crystalline rock types in Korea, to obtain the strain dependency characteristics of the cohesion and friction angle. A Cohesion-Weakening Friction-Strengthening (CWFS hereafter) model for each rock type was constructed and a series of compression tests were carried out numerically while varying confining pressures. The same tests were also conducted assuming the rock is Mohr-Coulomb material and results were compared.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.183-196
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• 2006

Rock joint roughness obtained from the camera-type 3D scanner was classified into waviness and unevenness. The classification criteria were established in the previous study; digital filtering was used to distinguish one from another. The classified and original profiles were used to produce metal moulds. For accurate machining of the moulds, the WEDM(Wire-cut Electric Discharge Machining) was adopted. Specimens were cast using high strength gypsum, and joint shear tests were performed by varying normal stress from low value to high one. Roughness mobilization characteristics depending on the asperity scale and the applied normal stress were investigated. A new equation was proposed to predict shear strength of rock joint, which can consider the characteristics of roughness mobilization and roughness parameters. The roughness quantification composed of waviness and unevenness was found to be a useful method to predict the joint shear strength.