• Tunnel and Underground Space
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• v.19 no.2
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• pp.86-94
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• 2009

A three dimensional rock joint element was developed considering fracture mechanics and subcritical crack growth to simulate non-linear behavior and the progressive failure of rock joints. Using this 3-D joint element, joint shear tests of rock discontinuities were simulated by a numerical method. The asperities on the joint surface began to fail at stress levels lower than the rock fracture toughness and continued progressively due to subcritical crack growth. As a result of progressive failing in each and every asperity, the joint showed non-linear stress-time behavior including stress hardening/softening and the reaching of a residual stress.

• Explosives and Blasting
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• v.36 no.4
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• pp.9-15
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• 2018

Since the rock fragmentation by blasting can affect the subsequent processes including loading, hauling and secondary crushing, its control is essential for the assessment of blasting efficiency as well as production cost. In this study, we were analyzed the rock fragmentation by the direction of artificial joint. The underground blasting experiments were performed after forming the vertical and horizontal artificial joints. The blast fragmentation was conducted by the split-desktop which is a 2D image processing program. As a result, it was found that the horizontal artificial joint was evaluated to have lower overall the size of muck pile than the vertical artificial joint and the distribution of the size of muck pile was varied. It is possible that the direction of artificial joint could suppress the occur of oversize muck pile and control to a certain size or less.

• Explosives and Blasting
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• v.23 no.2
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• pp.37-44
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• 2005

Recent studies reported that natural block size of rock and joint orientation highly affect on rock fragmentation. In this study, blasting test using high strength cement mortar was carried out to verify this fact. The result of this test indicated that fragmentation is influenced by the joint interval, and at same joint interval condition, fragmentation depends on joint orientation. These results are significantly coincident with field investigations.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.291-300
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• 2000

암반은 여러 가지 지질학적 요인들에 의해 형성된 수많은 절리면들을 경계로 하는 다양한 크기와 형상의 암석블럭들이 맞물려 평행상태를 이루고 있는 불연속체이다. 불연속 암반의 거동은 암석블럭을 이루는 무결암의 역학적 특성뿐만 아니라 암석블럭의 경계를 이루는 절리면들의 공간적 분포특성과 역학적 특성에도 큰 영향을 받는다. 불연속 암반의 거동해석을 목적으로 개발되고 있는 최근의 수치해석 기법들도 대부분 절리면의 영향을 효과적으로 해석에 반영시킬 수 있는 방법을 찾는데 집중하고 있다.(중략)

• Proceedings of the KSEG Conference
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• 2002.04a
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• pp.201-210
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• 2002

서울시 북동부의 서울화강암에 대한 암반 공학적 특성 중 터널과 도로 건설시 중요하게 취급되는 절리의 방향성, 절리간격, 절리밀도, 암석의 일축압축강도, 그리고 RQD 값을 수락산과 불암산지역으로 구분하여 비교, 분석하였다. 이 중 절리의 방향성, 절리간격과 절리밀도는 선조사법, 원형조사법, 그리고 면적조사법을 이용하여 야외에서 직접 측정하였다. 암석의 일축압축강도와 RQD의 측정은 시추코아의 표본이 필요하지만 이번 연구에서는 간단히 응용할 수 있는 대비공식을 이용하여 계산하였다. 측정된 대표적인 절리의 방향성은 두 지역에서 모두 3조의 방향성이 나타났으며 즉 2조의 수직정방절리와 저각으로 경사하는 1조의 판상절리로 판명되었으며 두 지역에서 서로 유사한 방향성을 갖는다. 측정된 절리밀도는 0.039-0.066/cm이었으며, 평균절리길이는 1.30-4.52m, 그리고 평균절리간격은 10.3cm에서 최대 59.6cm로 측정된 절리의 방향에 따라 변화가 심하다 또한 슈미트 해머 타격값에 근거한 절리면의 일축압축강도는 217 MPa에서 335 MPa로 매우 강한 암체였으며, 평균절리간격에 기초하여 계산된 이론적 RQD 값은 73.1-98.7%의 값을 갖는 것으로 나타났다.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.17-26
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• 2014

Tunneling-induced displacement in a jointed rock mass is an important factor to control tunnel stability and to secure a demanded space and construction quality. The magnitude of the inducible displacements is significantly affected by an elastic modulus and therefore, in a rock mass where a joint controls tunnel behavior, it is very important to estimate an elastic modulus of jointed rock mass reliably. Elastic modulus of jointed rock mass is affected by many factors such as rock type, joint condition, and loading condition. Nevertheless, most existing studies were focused on rough empirical relationships based on compressive loading conditions, which are different from tunnel excavation loading conditions, without a systematic approach of rock, joint, and loading conditions together. Therefore, this study considered rock and joint conditions systematically to estimate an elastic modulus of jointed rock mass under tunnel excavation loading. The controlled factors considered in this study are rock types and joint conditions (joint shear strength, joint inclination angle, number of joint sets, and joint spacing). Numerical parametric studies have been carried out with a consideration of different rock and joint conditions; the results have been compared with existing empirical relationships; and charts of elastic modulus change of different rock and joint conditions have been provided. The results are expected to have a great practical use for estimating the convergence induced by tunnel excavation in jointed rockmass.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.551-558
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• 2020

This note presents the calculation of nominal area for rock core specimen under direct shear testing condition. The initial nominal area was assumed as ellipsoid, and the equations for calculating the nominal area are derived. The normalized shear displacement and normalized nominal area have an identical relationship regardless of the ellipsoid shape. New testing constants and the generalized method were suggested to calculate the decrease of the nominal area. The method was applied to calculate the direct shear testing data and the changes of result were discussed.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.384-395
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• 2016

Both the roughness measurement tests and the multi-stage shear tests were carried out on the 110 rock joint samples in order to investigate the influences of rock type, joint roughness and normal stress on the shear behaviour of rock joints. Test samples were composed of quartz porphyry, dacite, granite and gneiss, which were classified into three detailed groups according to their JRC values. Roughness parameters of rock joints were analyzed by roughness measurement tests, and shear characteristics were also investigated by multi-stage shear tests. Both peak shear strength and shear stiffness were increased as both joint roughness and normal stress were increased, whereas dilation angles showed lower values at the lower roughness and higher normal stress conditions. Besides, shear characteristics obtained from all tests of four different rock types with different rock strengths showed irrelevant details, therefore the influences of both joint roughness and normal stress on shear behaviors were found to be more considerable than the strength of intact rock. The results obtained from both multi-stage shear tests and direct shear tests were finally compared, where the dilation angles obtained from multi-stage shear tests were found to be valid only for the first normal stress conditions.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.161-172
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• 2000

자연암석절리 및 인공 절리에 대하여 일정수직응력제어, 일정 수직하중제어 그리고 무한 강성제어가 가능한 암석 절리면 전단기 시험기를 개발하였다. 이 시험기는 전단변위에 의한 첩촉면적의 변화량을 계산하여 하중변화량을 조절하여 일정수직응력상태를 유지한다. 수직하중에 따른 시험기 강성에 의한 변화향이 제어 프로그램 내에서 제어되어 순수한 시편의 변위량을 출력하도록 하였다. 전단하중에 따른 시험기 강성에 의한 변위량은 상, 하부 전단상자의 상대변위 측정으로 최소화하였다. 전단거동 중의 자유도는 전당방향에 대하여 수평이도, 연직이동, 피칭, 롤링이 가능하도록 하였다. 자연절리면을 모사한 석고시편에 대하여 일정 수직응력 제어, 일정수직하중제어 그리고 무한 강성제어 조건으로 시험하여 제어상태 검증 및 비교를 하였다. 또한 경사각이 16.7˚와 22.6˚인 톱니형 시편에 대하여 시험한 결과 경사각 16.7˚와 22.6˚는 JRC로 10과 15를 나타내었으며, 첨두팽창각이 첨두전단강도에서 발생되며, Barton의 모델과 잘 일치함을 보였다.

• 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.