• Title/Summary/Keyword: Rock Fracture

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Physical and Particle Flow Modeling of Shear Behavior of Non-Persistent Joints

  • Ghazvinian, A.;Sarfarazi, V.;Nejati, H.;Hadei, M.R.
    • Proceedings of the Korean Society for Rock Mechanics Conference
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    • 2011.09a
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    • pp.3-21
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    • 2011
  • Laboratory experiments and numerical simulations using Particle Flow Code (PFC2D) were performed to study the effects of joint separation and joint overlapping on the full failure behavior of rock bridges under direct shear loading. Through numerical direct shear tests, the failure process is visually observed and the failure patterns are achieved with reasonable conformity with the experimental results. The simulation results clearly showed that cracks developed during the test were predominantly tension cracks. It was deduced that the failure pattern was mostly influenced by both of the joint separation and joint overlapping while the shear strength is closely related to the failure pattern and its failure mechanism. The studies revealed that shear strength of rock bridges are increased with increasing in the joint separation. Also, it was observed that for a fixed cross sectional area of rock bridges, shear strength of overlapped joints are less than the shear strength of non-overlapped joints.

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Factors affecting waterproof efficiency of grouting in single rock fracture

  • Lee, Hang Bok;Oh, Tae-Min;Park, Eui-Seob;Lee, Jong-Won;Kim, Hyung-Mok
    • Geomechanics and Engineering
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    • v.12 no.5
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    • pp.771-783
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    • 2017
  • Using a transparent fracture replica with aperture size and water-cement ratio (w/c), the factors affecting the penetration behavior of rock grouting were investigated through laboratory experiments. In addition, the waterproof efficiency was estimated by the reduction of water outflow through the fractures after the grout curing process. Penetration behavior shows that grout penetration patterns present similarly radial forms in all experimental cases; however, velocity of grout penetration showed clear differences according to the aperture sizes and water-cement ratio. It can be seen that the waterproof efficiency increased as the aperture size and w/c decreased. During grout injection or curing processes, air bubbles formed and bleeding occurred, both of which affected the waterproof ability of the grouting. These two phenomena can significantly prevent the successful performance of rock grouting in field-scale underground spaces, especially at deep depth conditions. Our research can provide a foundation for improving and optimizing the innovative techniques of rock grouting.

The influence of residual stress on the engineering behaviour of rock (잔류응력이 암석의 공학적 거동에 끼치는 영향)

  • 박형동
    • Tunnel and Underground Space
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    • v.5 no.4
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    • pp.363-375
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    • 1995
  • Critical literature review in this study revealed that there can be a significant influence of the residual stress on the engineering properties of rock. The review also showed that few number of research works on the quantification of the influence was attributed to the limitation of the two classical measurement techniques, viz, X-ray diffraction and mechanical relaxation method. In this study, a new way of approach was sought based on the assumption that residual stress up to the failure. A series of hoop tests conducted onthe samples from the limb of Carboniferous Limestone in Clevedon, England, revealed that (i) there is no preferential orientations of microcracks and minerals which have been widely believed as the main source of the strength anisotropy of rock; (ii) the anisotropy of the tensile strength of the limestone results from the influence of the residual stress; (iii) since jointing commenced within the fold, residual stored strain energy has been released preferentially in the direction perpendicular to the major joints(o$^{\circ}$ and 90$^{\circ}$); (ⅳ) during the hoop test making it much easier to create tensile fracture in these directons, viz 45$^{\circ}$ and 135$^{\circ}$)was released during the hoop test making it much easier to create tensile fracture in these directions, viz 45$^{\circ}$and 135$^{\circ}$;(v) the direction in which the stored strain energy may be presumed to be the least, required the greatest work to cause failure.

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Analysis of Relationship between 2-D Fabric Tensor Parameters and Hydraulic Properties of Fractured Rock Mass (절리성 암반의 이차원 균열텐서 파라미터와 수리적 특성 간의 상관성 분석에 관한 연구)

  • Um, Jeong-Gi;Han, Jisu
    • Tunnel and Underground Space
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    • v.27 no.2
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    • pp.100-108
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    • 2017
  • As a measure of the combined effect of fracture geometry, the fabric tensor parameters could quantify the status of the connected fluid flow paths in discrete fracture network (DFN). The correlation analysis between fabric tensor parameters and hydraulic properties of the 2-D DFN was performed in this study. It is found that there exists a strong nonlinear relationship between the directional conductivity and the fabric tensor component estimated in the direction normal to the direction of hydraulic conductivity. The circular radial plots without significant variation of the first invariant ($F_0$) of fabric tensor for different sized 2-D DFN block are a necessary condition for treating representative element volume (REV) of a fractured rock mass. The relative error (ER) between the numerically calculated directional hydraulic conductivity and the theoretical directional hydraulic conductivity decreases with the increase in $F_0$. A strong functional relation seems to exist between the $F_0$ and the average block hydraulic conductivity.

Penetration of Compacted Bentonite into the Discontinuity in the Excavation Damaged Zone of Deposition Hole in the Geological Repository (심층처분장 처분공 주변 굴착손상영역에 존재하는 불연속면으로의 압축 벤토나이트 침투)

  • Lee, Changsoo;Cho, Won-Jin;Kim, Jin-Seop;Kim, Geon-Young
    • Tunnel and Underground Space
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    • v.30 no.3
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    • pp.193-213
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    • 2020
  • A mathematical model to simulate more realistically the penetration of compacted bentonite buffer installed in the deposition hole into the discontinuity in the excavation damaged zone formed at the inner wall of the deposition hole in the geological repository for spent fuel is developed. In this model, the penetration of compacted bentonite is assumed to be the flow of Bingham fluid through the parallel planar rock fracture. The penetration of compacted bentonite is analyzed using the developed model. The results show that the maximum penetration depth of compacted bentonite into the rock fracture is proportioned to the swelling pressure of saturated compacted bentonite and the aperture of rock fracture. However, it is in inverse proportion to the yield strength of compacted bentonite. The viscosity of compacted bentonite dominates the penetration rate of compacted bentonite, but has no influence to the maximum penetration depth.

Numerical Study on the Crack-propagation Controlling in Blasting Using Notched Charge Hole (노치 장약공을 이용한 발파균열제어에 관한 수치해석적 연구)

  • Cho, Sang-Ho;Park, Seung-Hwan;Kim, Kwang-Yeom;Nakamura, Yuichi;Kaneko, Katsuhiko
    • Explosives and Blasting
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    • v.26 no.1
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    • pp.49-55
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    • 2008
  • Mechanical excavation techniques employing tunnel boring machines (TBM) and rock splitters have been proposed to minimize rock damage for tunnel and underground waste repository facilities. Such a mechanical excavation, however, is extremely expensive and not applicable in all cases. For these reasons, controlled blasting using notched charge holes have been suggested to achieve crack growth along specific directions and inhibit growth along other directions. This study introduces a dynamic fracture process analysis code to simulate fracture processes of rock which has a notched charge hole.

Notch Sensitivity Analysis for the Rock Fracture Toughness (암석의 파괴인성계수와 균열감응도의 해석)

  • 백환조
    • Tunnel and Underground Space
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    • v.7 no.2
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    • pp.143-149
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    • 1997
  • 암석의 파괴인성계수(fracture toughness)는 균열의 성장에 대한 암석의 저항을 나타낸다. 실험실에서 측정한 파괴인성계수는 일반적인 암석의 불균질성이나 이방성 외에도 시험편의 형상이나 하중조건에 의하여 크게 영향을 받는다. 따라서, 제한된 수의 시험편을 사용하여 측정된 파괴인성계수는 자료의 분산이 심하므로 실제 적용에 있어서 문제가 된다. 균열감응도란 파괴인성계수의 측정에 사용되는 시험편의 형상에 따라 결정되는 지수로서, 시험편의 파괴가 균열의 성장에 의한 것인지, 혹은 인장강도에 의한 것인지를 판별하는 기준이 된다. 이러한 균열감응도를 파악하여 암석의 파괴인성계수 측정에 유효한 시험편의 크기나 초기균열 길이의 범위를 설정할 수 있다. 이는 또한 실험실에서 측정된 차괴인성계수의 유효성 여부를 판별하는 기준으로 사용될 수 있다. 본 논문에서는 암석의 파괴인성계수의 측정에 흔히 사용되는 몇 가지 형태의 시험편들에 대하여 균열감응도를 계산하고 이에 따른 초기균열 길이의 범위를 제시하고자 한다.

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Groundwaterflow analysis of discontinuous rock mass with probabilistic approach (통계적 접근법에 의한 불연속암반의 지하수 유동해석)

  • 장현익;장근무;이정인
    • Tunnel and Underground Space
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    • v.6 no.1
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    • pp.30-38
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    • 1996
  • A two dimensional analysis program for groundwater flow in fractured network was developed to analyze the influence of discontinuity characteristics on groundwater flow. This program involves the generation of discontinuities and also connectivity analysis. The discontinuities were generated by the probabilistic density function(P.D.F.) reflecting the characteristics of discontinuities. And the fracture network model was completed through the connectivity analysis. This program also involves the analysis of groundwater flow through the discontinuity network. The result of numerical experiment shows that the equivalent hydraulic conductivity increased and became closer to isotropic as the density and trace length increased. And hydraulic head decreased along the fracture zone because of much water-flow. The grouting increased the groundwater head around cavern. An analysis of groundwater flow through discontinuity network was performed around underground oil storage cavern which is now under construction. The probabilistic density functions(P.D.F) were obtained from the investigation of the discontinuity trace map. When the anisotropic hydraulic conductivity is used, the flow rate into the cavern was below the acceptable value to maintain the hydraulic containment. But when the isotropic hydraulic conductivity is used, the flow rate was above the acceptable value.

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DEM generation of Rock Slope using Laser Scanning and Digital Stereo Photogrammetry (3D laser scanning 및 수치사진측량을 이용한 암반 사면의 DEM 추출 기법)

  • 정창엽;박형동
    • Tunnel and Underground Space
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    • v.13 no.3
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    • pp.207-214
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    • 2003
  • To obtain Digital Elevation Model(DEM) from an exposed rock mass, techniques such as laser scanning and digital stereo photogrammetric technique are recently applied. We have obtained the DEM of the rock slope using above techniques in this study, and examined a suitability and improvement of the photogrammetry for the rock slope by overlapping the DEM. This study can be applied to the measurement of fracture orientations, the prediction of rock joint network, and the analysis on the change of the rock slope.

Fracture Developing History and Density Analysis based on Grid-mapping in Bonggil-ri, Gyeongju, SE Korea (경주시 봉길리 지역의 단열발달사 및 단열밀도 해석)

  • Jin, Kwang-Min;Kim, Young-Seog
    • The Journal of Engineering Geology
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    • v.17 no.3
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    • pp.455-469
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    • 2007
  • The study area, Bonggil-ri, Gyeongju, SE Korea, is composed of Cretaceous sedimentary rocks, and Tertiary igneous rocks and dykes. A research on fracture developing history and density distribution was carried out on well exposed Tertiary granites. The fractures developed in this area have the following sequence; NW-SE trending duo-tile shear bands (set a), NNW-SSE trending extensional fractures (set d), WNW-ESE trending extensional or normal fractures (set b), NE-SW trending right-lateral fractures (set c), WNW-ESE trending reverse fault reactivated from normal faults (set e) and NW-SE trending left-lateral faults reactivated from shear bands (set a) under brittle condition. According to the result of fracture density analysis, the fracture density in this area depends on rock property rather than rock age, and also higher fracture density is observed around fault damage zones. However, this high fracture density may also be related to the cooling process associated with dyke intrusion as well as rock types and fault movement. Regardless of the reason of the high fracture density, high fracture density itself contributes to fluid flow and migration of chemical elements.