• The Journal of Engineering Geology
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• v.12 no.4
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• pp.405-419
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• 2002

Fracture roughness of rock specimens is observed by a new confocal laser scanning microscope (CLSM; Olympus OLS1100). The wave length of laser is 488 nm, and the laser scanning is managed by a light polarization method using two galvano-meter scanner mirrors. The function of laser reflection auto-focusing enables us to measure line data fast and precisely. The system improves resolution in the light axis (namely z) direction because of the confocal optics. Using the CLSM, it is Possible to measure a specimen of the size up to $10{\;}{\times}{\;}10{\;}cm$ which is fixed on a specially designed stage. A sampling is managed in a spacing $2.5{\;}\mu\textrm{m}$ along x and y directions. The highest measurement resolution of z direction is $10{\;}\mu\textrm{m}$, which is more accurate than other methods. Core specimens of coarse and fine grained granite are provided. Fractures are artificially maneuvered by a Brazilian test method. Measurements are performed along three scan lines on each fracture surface. The measured data are represented as 2-D and 3-D digital images showing detailed features of roughness. Line profiles of the coarse granites represent more frequent change of undulation than those of the fine granite. Spectral analyses by the fast Fourier transform (FFT) are performed to characterize the roughness data quantitatively and to identify influential frequency of roughness. The FFT results suggest that a specimen loaded by large and low frequency energy tends to have high values of undulation change and large wave length of fracture roughness.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.226-233
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• 1998

Microcracks in rock materials, whether natural or induced, provide useful information on the engineering performance of in situ rockmasses. A population of preferentially oriented microcracks has observable effects on the physical properties of a rockmass, but their effects may not be evident if the rock material is highly anisotropic due to other causes. An experimental program was undertaken to investigate the effect of rock fabrics on the physical properties of rock materials. In this study, anisotropy in the circumferential wave velocity and the direction of induced fractures under axial point loading were measured. Rock specimens (NX-size) of the leucocractic Pocheon granite were cored from rock blocks, retaining the relative directions of each specimen. Another set of specimens was prepared from the rock cores of the same meterial, obtained in the field. The master orientation line (MOL) was set to be the representative direction of the microcracks in the specimen. Variation of the circumferential wave velocity of each specimen was then measured along the core, keeping the MOL as reference. The direction of the minimum wave velocity was nearly perpendicular to the direction of the MOL. Coring of smaller-sized (EX-size), concentric specimens from the NX specimens were then followed, and axial point loading was applied. The direction of induced fractures due to axial point loading was closely related to the MOL direction, confirming the prior test result.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.396-408
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• 2016

Rock fracture mechanics has been widely applied to various fields of rock and civil engineering. But most researches covered mode I behavior, though mode II behavior is dominant in rock engineering. Until now, there is only one ISRM suggested method for mode II toughness of rock. A new SCC (Short Core in Compression) mode II toughness test method was developed considering 1) application of confining pressure, 2) easiness of notch creation, 3) utilization of existing equipment, 4) simple test procedure. The stress intensity factors were determined by 3D finite element method considering line and distributed loading conditions. The tests with granite specimens were carried out using MTS 815 rock test system with a loading rate of 0.002 mm/s. The mean value of mode II fracture toughness of granite showed $2.33MPa{\sqrt{m}}$. Mode I toughness of the same granite was $1.12MPa{\sqrt{m}}$, determined by Brazilian disk test and $K_{IIC}/K_{IC}=2.08$. The smooth fracture surface with rock powder formation also supported mode II behavior of SCC method. The SCC method can be used for the determination of mode II fracture toughness of rocks based on the current results.

• Journal of the Korean earth science society
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• v.26 no.7
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• pp.630-639
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• 2005

The purpose of this study was to investigate the classifying ability of the igneous rocks with the naked eye for 36 preservice science teachers. For this, we selected six specimens of igneous rocks that consisted of rhyolite, andesite, basalt, granite, diorite, and gabbro, and performed the questionnaire with them. Preservice science teachers needed the average of 3 tools to classify the rocks. Most of the selected tools were loupe, streak plate, hammer and Mohs’ hardness scale. Many preservice science teachers selected basalt and granite samples to classify igneous rocks among 6 kinds of the rocks which were exhibited. However, the results of the identification with the naked eye showed that the right answer rate was significantly different based on what rock sample had been selected. Nobody gave the right answer among 10 students who chose the rhyolite sample, but all of 36 students who picked the basalt sample answered correctly. And $62\%$ of 8 students who chose the andesite sample, 62% of 32 student choosing granite, $7\%$ of 13 students choosing diorite and $44\%$ of 9 students choosing gabbro were correctly answered. In identifying igneous rock samples with the naked eye, most subjects relied on vesicular texture to basalt, and they used textural, color and empirical characters to granite. But, some felt more or less difficulty to distinguish between intermediate and light colors and to recognize porphyry.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.276-283
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• 2012

Changes in rock properties due to freezing and thawing cycles ranging from $-20^{\circ}C$ to $10^{\circ}C$ were checked for the typical Korean rocks: granite (weathered), limestone, sandstone, tuff, shale and basalt. The porosity, seismic velocity, shore hardness and specific gravity were measured every 10 cycles for each type of rock up to 40 cycles. The specific gravity was rarely changed. Granite (w), shale and basalt decreased gradually in their shore hardness and seismic velocity values, these values for limestone, sandstone and tuff changed only a very little. The porosity increased in the granite (w), shale and basalt, whereas in the others it did not change. Due to the low tensile strength with high porosity, granite (w), shale and basalt were susceptible to the F-T cycles. A linear regression equation was calculated based on the experiment results according to properties and types of rock. The relationship between the freeze-thaw sensitivity (=initial porosity/initial tensile strength) and the coefficients of the regression equation was examined. With additional experimental data, the coefficients of the regression equation can be estimated using the F-T sensitivity. This makes it possible to predict the properties of rock as affected by freeze-thaw weathering by only measuring the initial properties without knowledge of the regression equation coefficients for each type of rock.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.273-291
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• 2020

The strength characteristics of the three orthogonal splitting planes, known as rift, grain and hardway planes in granite quarries, were examined. R, G and H specimens were obtained from the block samples of Jurassic granites in Geochang and Hapcheon areas. The directions of the long axes of these three specimens are perpendicular to each of the three planes. First, The chart, showing the scaling characteristics of three graphs related to the uniaxial compressive strengths of R, G and H specimens, were made. The graphs for the three specimens, along with the increase of strength, are arranged in the order of H < G < R. The angles of inclination of the graphs for the three specimens, suggesting the degree of uniformity of the texture within the specimen, were compared. The above angles for H specimens(θ^H, 24.0°~37.3°) are the lowest among the three specimens. Second, the scaling characteristics related to the three graphs of RG, GH and RH specimens, representing a combination of the mean compressive strengths of the two specimens, were derived. These three graphs, taking the various N-shaped forms, are arranged in the order of GH < RH < RG. Third, the correlation chart between the strength difference(Δσ_t) and the angle of inclination(θ) was made. The above two parameters show the correlation of the exponential function with an exponent(λ) of -0.003. In both granites, the angle of inclination(θ^RH) of the RH-graph is the lowest. Fourth, the six types of charts, showing the correlations among the three kinds of compressive strengths for the three specimens and the five parameters for the two sets of microcracks aligned parallel to the compressive load applied to each specimen, were made. From these charts for Geochang and Hapcheon granites, the mean value(0.877) of the correlation coefficients(R²) for total density(Lt), along with the frequency(N, 0.872) and density(ρ, 0.874), is the highest. In addition, the mean values(0.829) of correlation coefficients associated with the mean compressive strengths are more higher than the minimum(0.768) and maximum(0.804) compression strengths of three specimens. Fifth, the distributional characteristics of the Brazilian tensile strengths measured in directions parallel to the above two sets of microcracks in the three specimens from Geochang granite were derived. From the related chart, the three graphs for these tensile strengths corresponding to the R, G and H specimens show an order of H(R1+G1) < G(R2+H1) < R(R1+G1). The order of arrangement of the three graphs for the tensile strengths and that for the compressive strengths are mutually consistent. Therefore, the compressive strengths of the three specimens are proportional to the three types of tensile strengths. Sixth, the values of correlation coefficients, among the three tensile strengths corresponding to each cumulative number(N=1~10) from the above three graphs and the five parameters corresponding to each graph, were derived. The mean values of correlation coefficients for each parameter from the 10 correlation charts increase in the order of density(0.763) < total length(0.817) < frequency(0.839) < mean length(Lm, 0.901) ≤ median length(Lmed, 0.903). Seventh, the correlation charts among the compressive strengths and tensile strengths for the three specimens were made. The above correlation charts were divided into nine types based on the three kinds of compressive strengths and the five groups(A~E) of tensile strengths. From the related charts, as the tensile strength increases with the mean and maximum compressive strengths excluding the minimum compressive strength, the value of correlation coefficient increases rapidly.

• Journal of Industrial Technology
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• v.10
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• pp.57-67
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• 1990

Uniaxial compression tests are performed under various loading rates to study the influence of loading rate on the compressive strengths and deformation behaviours. The rock samples adopted in this experiments are Onyang granite, Hambaek sandstone, Hambaek shale and Donghae limestone. Total 120 specimens are prepared for this study. As the loading rate increases from static to dynamic state which is about the level of $800{\sim}1,400kgf/cm^2/sec$, the uniaxial compressive strengths are also increased within the range of 40%. And Young's modulus and Poisson's ratio show similar trends but have a little lower rates of increase when compared with that of uniaxial compressive strength.

• Economic and Environmental Geology
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• v.21 no.4
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• pp.359-365
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• 1988

Extensive sets of data on the mechanical properties of more than 1000 granite specimens were analyzed to derive the relationships of the various properties: those are, (1) density, (2) porosity, (3) absorption ratio, (4) sonic wave velocity, (5) uniaxial compressive strength, (6) tensile strength, and (7) dynamic & static Young's moduli. The results will be of use to understand the mechanical characteristics of granites and some unknown properties can be estimated from the others. The various equations derived from the least square regression analysis and a brief description of the correlations are presented in this paper.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.31-40
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• 1993

The vibration-proof material normally used in structural components of precision machinery or measuring instruments requires higher damping in vibration and better characteristics in dimensional stability and rigidity to accomplish the quality assurance of the products. In this study the ferrite-resin material, which is the mixture of epoxy resin and the oxidized steel (Fe$_{3}$O$_{4}$: ferrite) in consideration of characteristics of aggregator and binder, is developed and investigated as one of vibration-proof materials. Four kinds of composite plates for experiments are made by adding another filler materials such as steel powder, granite powder and carbon-fiber sheet to the basic ferrite-resin matrix. Their characteristics are compared with a cast iron specimen which has the same bending rigidity as other specimens. The ferrite-resin material gives the best damping effect in the motor-induced vibration test. Therefore, the material can be applied to the manufacturing industry for vibration damping of machine elements.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.1-8
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• 2017

An experimental technique for determining the spalling strength of rock-like materials under a high strain rate is developed. It is observed that the spalling strength of a specimen can be determined by only knowing the wavelength, loading peak value and length of the first spallation of an incident wave under a specific loading waveform. Using this method in combination with a split-Hopkinson pressure bar (SHPB) and other experimental devices, the spalling strength of granite specimens under a high strain rate is tested. Comparisons with other experimental results show that the new measuring method can accurately calculate the dynamic tensile strength of rock materials under a high strain rate.