• Tunnel and Underground Space
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• v.19 no.2
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• pp.95-106
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• 2009

Numerical analysis of the progressive failure of a rock slope was conducted using a 3-D rock joint element considering fracture mechanics and subcritical crack growth of asperities in the rock joints. Even though the stress state in the rock slope is not changing, the elapse of time causes subcritical crack growth to break asperities in the joints. The increase of broken asperities causes failure of joints in the rock slope and the increase of failed joints results in failure of a jointed rock slope. As a result, the progressive failure of a jointed rock slope due to the gradual breaking of small asperities along joints generated by subcritical crack growth occurs at a lower stress than if rock failure occurred by exceeding the static strength or fracture toughness.

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

• Tunnel and Underground Space
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• v.10 no.1
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• pp.45-58
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• 2000

Cyclic shear test system, which is capable of measuring flow rate inside rock joint, was established to investigate the hydraulic behavior of rough rock joints under various loading conditions. Laboratory hydraulic tests during compression and shear were conducted for artificial rough rock joints. Prior to tests, aperture characteristics of specimens were examined by measuring surface topography. Permeability changes under compression were well approximated with several hydraulic model. Hydraulic behavior conformed to dilation characteristics in the first stage, and permeability increased with increase of dilation. As the shear displacement progressed, flow rate became somewhat constant due to gouge production and offset of apertures. Hydraulic behavior under cyclic shear loading was also influenced by the degradation of asperities and gouge production. In addition. the relation between hydraulic aperture and mechanical aperture under compression and shear loading was investigated and compared.

• Tunnel and Underground Space
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• v.9 no.2
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• pp.141-148
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• 1999

Distinct element simulation in jointed rock masses is largely dependent upon the joint constitutive equation used. This paper describes the differences between the Barton-Bandits (BB) and the Mohr-Coulomb (MC) joint constitutive models for the stability analysis of the jointed rock slopes. The BB model, which allows the modelling of the dilation accompanying shear, predicts results very similar to the present condition of slopes. Consequently the 10 cm thick shotcrete was proposed for the reinforcement of those slopes. The MC model, however, in which the dilation angle is constant, is relatively insensitive to the behaviors of joints.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.61-70
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• 2013

This paper presents the results of a two-dimensional finite element analysis of end bearing capacity of single pile installed in fractured rock mass. A number of cases were analyzed using Hoek-Brown criterion that can consider the condition of rock joints. Considering a wide range of joint conditions in which the pile is embedded into the rock, GSI was set as a main parameter. And the effects of pile diameter, unconfined compressive strength of rock and Hoek-Brown constant $m_0$ were considered. Based on parameter study, end bearing load factor graphs were suggested.

• Journal of the Korean Geotechnical Society
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• v.33 no.4
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• pp.5-15
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• 2017

Three-hinge failure occurs in a jointed rock slope with a joint set parallel with slope and a conjugate joint set. Limit Equilibrium Method (LEM) and Finite Element Method (FEM) which are commonly used for slope design, are not suitable for evaluating stability against three-hinge failure, and this study performed parametric study to analyze the failure mechanism and to find influence factors causing three-hinge failure using UDEC which is a commercial two-dimensional DEM based numerical program. Numerical analyses were performed for various joint structural conditions and joint properties as well as ground water conditions. It was found that pore water pressure is the main factor triggering the three-hinge failure and the mode of failure depends on friction angle of basal joint and bedding joint set. The results obtained from this study can be used for adequate and economic footwall slope reinforcement design and construction.

• Tunnel and Underground Space
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• v.29 no.1
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• pp.64-74
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• 2019

Behavior of a rock block consisting of rock joints during excavation of an underground opening is an important factor for the mechanical stability of the opening. In this study, the behavior of a rock block under different geostatic stress and joint property conditions was analyzed quantitatively. The behavior of the rock block analyzed by 3DEC numerical analysis was compared with that of the theoretical calculation, and the error between the theoretical value and the numerical analysis result was analyzed under various geostatic stress and joint property conditions. The result of the stability analysis of a rock block showed less than 5% of error with numerical simulation result, which verified the applicability of the purposed analytic solution.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2004.10a
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• pp.101-117
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• 2004

• The Journal of Engineering Geology
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• v.11 no.1
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• pp.1-11
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• 2001

The geological characteristics of Korea are that we can encounter the rock layer only after 10m of excavation, methods to presume the rock pressure distribution of the rock layer is urgently needed. When using the existing empiric science of Terzaghi-Peck, Tschebotarioff to measure the rock pressure of the rock layer, underestimate the real strength because of the cohesion is ignored. Therefore calculating the horizontal sliding force of wedge block, which includes the dips and shear strength of discontinuities and surcharge load etc., think to be to getting a closer rock stress of the real rock pressure acting upon the earth structure in rock mass. This research use Coulomb soil pressure theory assuming that the backfill soil will yield wedge failure when it has cohesion, applying Prakash-Saran(l963), and then it uses equilibrium of force and shear strength $\tau$=c+$\sigma$tan $\Phi$ of the cliscontinuities. Analyzing shear strength and dips of cliscontinuities using calculated theory according to the status of discontinuities aperture, we were able to find out that because the cohesion and friction angle of the rock layer itself is large enough, how the dip directions and dips facing the excavation face is the only factor deciding whether or not the rock stress is applied. The evaluated theory of this research should be strictly estimated, so that the many parameters such as c, $\Phi$value, types and structures of rock class, excessive lateral pressure, dynamic load, earthquake, needed later when calculating shear strength of discontinuities and especially the ground water effect acting on rock layer should be coumpted with many measuring data achieve at the insite to study the application.

• Tunnel and Underground Space
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• v.13 no.6
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• pp.486-494
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• 2003

When the orientations of joints are measured on a rock exposure, there are frequent cases that are difficult to approach by the surveyor to the target joints or to set up scanlines on the slope. In this study, to complement such limit and weak points, a new algorithm was developed to interpret joint orientation from analyzing the images of rock slope. As a method of arranging the multiple images of a rock slope, the multistage convergent photographing system was introduced to overcome the limitation of photographing direction which existing method such as parallel stereophotogrammetric system has and to cover the range of image measurement, which is the overlapping area between the image pair, to a maximum extent. To determine camera parameters in the perspective projection equation that are the main elements of the analysis method, a new method was developed introducing three ground control points and single ground guide point. This method could be considered to be very simple compared with other existing methods using a number of ground control points and complicated analysis process. So the global coordinates of a specific point on a rock slope could be analyzed with this new method. The orientation of a joint could be calculated using the normal vector of the joint surface which can be derived from the global coordinates of several points on the joint surface analyzed from the images.