• The Journal of Engineering Geology
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• v.26 no.4
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• pp.593-600
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• 2016

To understand the mechanical properties of rock masses and intact rock in Korea, data from 4,280 in situ and laboratory tests from 107 tunnels on general national roads were analyzed. The mechanical properties (unit weight, cohesion, friction angle, modulus of deformation, Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, coefficient of permeability, and specific gravity) were analyzed by rock types and strength of rock in each rock type. The results of analysis, the mean specific gravity was highest in gneiss. The coefficient of permeability and Poisson's ratio show the highest mean values in granite and metamorphic rock, respectively. In addition, the unit weight, cohesion and friction angle in sedimentary rock, modulus of deformation, Young's modulus, uniaxial compressive strength and tensile strength in volcanic rock have the highest mean values. The values for each mechanical property showed wide ranges by the heterogeneity and anisotropy of rock masses in spite of detailed analysis by rock type and classification of rocks according to the strength.

• 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.

• Tunnel and Underground Space
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• v.1 no.2
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• pp.181-203
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• 1991

The effects of geologic structures such as rock joins and bedding planes on the thermal conductivity of a discontinuous rock mass are studied. The expressions for the equivalent thermal conductivities of jointed rock masses are derived and found to be anisotropic. The degree of anisotropy depends primarily on the thermal properties contrast between the joint phase and surrounding intact rock, the joint density expressed as volume fraction and the inclination angle of the joint. Within the context of 2-dimensional finite element heat transfer scheme, the isotherms around a circular hole are analyzed for both the isotropic and anisotropic rock masses in 3 different thermal boundary conditions. i.e. temperature, heat flux and convection boundary conditions. The temperature in the stratified anisotripic rock mass is greatly influenced by the thermal properties of the rock formation in contact with the heat source. Using the excavation-temperature coupled elastic plastic finite element method, analyzed is the thermo-mechanical stability of a circular opening subjected to 10$0^{\circ}C$ at a depth of 527m. It is found that the thermal stress concentration was enough to deteriorate the stability and form a plastic yield zone around the opening, in contrast to the safety factor greater than 2 resulted form the excavation-only analysis.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.271-285
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• 2020

In this study, a numerical experiment related to the stress-strain analysis was performed on 3-D discrete fracture network(DFN) systems based on the distinct element method to evaluate the effect of joint geometry on deformability of jointed rock masses. Using one or two joint sets with deterministic orientation, a total of 12 3-D DFN blocks having 10m cube domain were generated with different joint density and size distribution. Directional deformation modulus of the DFN cube blocks were estimated along the axis directions of 3-D cartesian coordinate. In addition, deviatoric stress directions were chosen at every 30° of trend and plunge in 3-D for some DFN blocks to examine the variability of directional deformation modulus with respect to joint geometry. The directional deformation modulus of the DFN block were found to reduce with the increase of joint size distribution. The increase in joint density was less likely to have a significant effect on directional deformation modulus of the DFN block in case of the effect of rock bridges was relatively large because of short joint size distribution. It, however, was evaluated that the longer the joint size, the increase in the joint density had a more significant effect on the anisotropic deformation modulus of the DFN block. The variation of the anisotropic deformation modulus according to the variations in joint density and size distribution was highly dependent on the number of joint sets and their orientation in the DFN block. Finally, this study addressed a numerical procedure for stress-strain analysis of jointed rock masses considering joint geometry and discussed a methodology for practical application at the field scale.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.47-55
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• 2013

To analyze lateral displacement of excavation walls exposed during the construction of Subway Line 1 in the Daegu region, inclinometer measurement data for sites D4, D5, and Y6 are investigated from the perspective of engineering geology. The study area, in the Banyawol Formation, Hayang Group, Gyeongsang Supergroup, is in the lower part of bedrock of andesitic volcanics, calcareous shale, sandstone, hornfels, and felsite dykes that are unconformably overlain by soil. The rock mass around the D4 site is classified as RMR-V grade and the maximum lateral displacement of 101.39 mm, toward N34W, was measured at a bedding-parallel fault, at a depth of 12 m. The rock mass around the D5 site is classified as RMR-IV grade and the maximum lateral displacement of 55.17 mm, toward the south, was measured at a lithologic contact between shale and felsite, at a depth of 14 m. The rock mass around the Y6 site is classified as RMR-III grade and the maximum lateral displacement of 12.65 mm, toward S52W, was measured at an unconformity between the soil and underlying bedrocks, at a depth of 7 m. The directions of lateral displacement in the excavation walls are vector sums of the directions perpendicular to the excavation wall and horizontally parallel to the excavation wall. Lateral displacement graphs according to depth in the soil profile show curvilinear trajectories, whereas those in bedrock show straight and rapid-displacement trajectories.

• Tunnel and Underground Space
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• v.18 no.4
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• pp.252-262
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• 2008

In the uniaxial compressive test of a single specimen of transversely isotropic rock, its 5 independent elastic constants can not be defined since maximum 4 independent strain measurements are available theoretically. In order to solve this problem, one equation proposed by Saint Venant in 19C and confirmed by Lekhnitskii through the test experiences has been used for long time. Accordign to authors' experiences, however, this equation turned out to give erroneous elastic constants in some cases. Three new equations are suggested and their compatibilities are discussed in this paper. As the results of the analyses of the models, Lekhnitskii's suggested equation is effective for the specimen with the high dip angle whereas it results in the large erred output for that with dip angle less than $25{\sim}30$. It was found that the effectivenesses of three suggested equations and their compatibilities are subject to the dip angle and not to the amounts of elastic constants. Guide map to the selection of the compatible one of those suggested equations is presented as a result of the study.

• The Journal of Engineering Geology
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• v.21 no.3
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• pp.221-230
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• 2011

The movement of rock cut slopes may result in upheaval of an adjacent road. Because most cut slopes consist of rock, road upheaval due to the movement of a cut slope is a rare phenomenon in Korea. We found that the movement of rock slopes which are heavily weathered and with strongly developed weak zones is governed by circular failure of the overall rock formation rather than by failure along discontinuities. The results of a numerical analysis revealed that the application of a ubiquitous joint model in a continuum analysis is appropriate for anisotropic rocks (e.g., schist) and for slopes for which the stability is influenced by a particular discontinuity. The results of a field investigation and numerical analyses suggest that retaining walls and anchors should be used to stabilize rock slopes and that real-time monitoring equipment should be installed to assess the reinforcing effect of the remedial measures.

• Tunnel and Underground Space
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• v.23 no.5
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• pp.383-391
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• 2013

A number of true triaxial tests on rock samples have been conducted since the late 1960 and their results strongly suggest that the intermediate principal stress has a considerable effect on rock strength. Based on these experimental evidence, various 3-D rock failure criteria accounting for the effect of the intermediate principal stress have been proposed. Most of the 3-D failure criteria, however, are focused on the phenomenological description of the rock strength from the true triaxial tests, so that the associated strength parameters have little physical meaning. In order to confirm the likelihood that the intermediate principal stress dependency of rock strength is related to the presence of weak planes and their distribution to the preferred orientation, true triaxial tests are simulated with the transversely isotropic rock model. The conventional Mohr-Coulomb criterion is extended to its anisotropic version by incorporating the concept of microstructure tensor. With the anisotropic Mohr-Coulomb criterion, the critical plane approach is applied to calculate the strength of the transversely isotropic rock model and the orientation of the fracture plane. This investigation hints that the spatial distribution of microstructural planes with respect to the principal stress triad is closely related to the intermediate principal stress dependency of rock strength.

• Tunnel and Underground Space
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• v.18 no.4
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• pp.300-311
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• 2008

In this study, scaled model tests were performed to investigate the stability of three parallel tunnels. Seven types of test models which had respectively different pillar widths, tunnel sectional shapes, support conditions and ground conditions were experimented, where crack initiating pressures and deformation behaviors around tunnels were investigated. In order to evaluate the effect of pillar widths on stability, various models were experimented. As results, the models with shallower pillar widths proved to be unstable because of lower crack initiating pressures and more tunnel convergences than the models with thicker pillar widths. In order to find the effect of tunnel sectional shape on stability, the models with arched, semi-arched and rectangular tunnels were experimented. Among them rectangular tunnel model was the most unstable, where the arched tunnel model with small radius of roof curvature was more stable than semi-arched one. The model with rockbolt showed higher crack initiating pressure and less roof lowering than the unsupported model. The deformation behaviors of tunnels in the anisotropic ground model were quite different from those in the isotropic ground model. Futhermore, the results of FLAC analysis were qualitatively coincident with the experimental results.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.105-115
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.