• Tunnel and Underground Space
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• v.27 no.5
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• pp.333-342
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• 2017

In this study, the heterogeneity of internal structure of various igneous rocks acquired in Korea was quantified and correlated with the seismic velocity and the point load strength. Three-dimensional X-ray Computed Tomography (CT) was used to obtain information on the internal structure of the rock specimen, and the representative unit length (LR) was calculated by applying a statistical technique to the CT images. We also proposed an estimation equation to predict the mechanical properties of rocks from the relationship between LR, acoustic velocity and point load strength. In the proposed method, it is shown that the characterization of internal structure of rocks could be utilized as an indirect index to account for the mechanical behavior of rocks by substituting physical laboratory testing for non-destructive test.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.1133-1138
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• 2009

This study was conducted in order to know the internal application of the critical strain graph. To evaluate critical strain graph, we carried out an uniaxial compression test with some of internal rocks: sandstone, shale, weathered granite, and pink granitic. Based on the uniaxial compression test, we deduced relations among critical strain, failure strain, uniaxial compression strength and modulus of elasticity. As a result, the study has found out the rocks, which have been tested, can be possibly evaluated by critical strain graph.

• Geomechanics and Engineering
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• v.27 no.6
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• pp.615-626
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• 2021

The main objective of this study is to present a fast and reliable approach to predict the swelling potential of clay-bearing rocks. Investigations showed that there is a good correlation between the swelling potential of a rock and its desire to absorb water due to its clay content which could be measured using the "Contact Angle" test as one of the most common ways to determine the wettability. In this test, the angle between a water drop and the flat rock surface on which it rests is measured. The present method is very fast and returns repeatable results and requires minimal sample preparation. Only having a saw-cut surface of a sample with any shape is all one needs to perform this test. The logic behind this approach is that the swelling potential of a rock is a function of its mineral content and molecular structure, which are not only distributed in the bulk of the sample but also reflected on its surface. Therefore, to evaluate swelling behavior, it is not necessary to wait for a sample to get wet all the way to its "internal structure" (which, due to the low permeability of clay-bearing rocks, is very slow and time-consuming). Instead, one can have a good sense of swelling potential by studying its surface. Parametric studies on the effect of moisture content, porosity, and surface roughness on the contact angle measurements showed that using a saw-cut oven-dried sample is a convenient way to evaluate the swelling potential by this method.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.33-40
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• 2015

Volcanic rocks in Jeju Island indicate the differences in geological and mechanical characteristics from region to region, and have vesicular structure caused by various environmental factors. In this study, triaxial compressive strength tests were conducted for intact rocks sampled in northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island. The estimated cohesion and internal friction angle from the results of triaxial compression tests were compared and analyzed with absorption, a parameter representing the vesicular properties of basalts in Jeju Island. As a result, it was found that the relationship between cohesion and absorption could be classified clearly, considering two different linear relationships in bulk specific gravity and absorption. As the absorption increases, the cohesion decreases exponentially. In addition, the internal friction angle decreases almost linearly with increasing in the absorption, regardless of the relationships in bulk specific gravity and absorption.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.273-284
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• 2018

A detailed understanding of the mechanical behaviors for crushed coal rocks after grouting is a key for construction in the broken zones of mining engineering. In this research, experiments of grouting into the crushed coal rock using independently developed test equipment for solving the problem of sampling of crushed coal rocks have been carried out. The application of uniaxial compression was used to approximately simulate the ground stress in real engineering. In combination with the analysis of crack evolution and failure modes for the grouted specimens, the influences of different crushed degrees of coal rock (CDCR) and solidified grout strength (SGS) on the mechanical behavior of grouted specimens under uniaxial compression were investigated. The research demonstrated that first, the UCS of grouted specimens decreased with the decrease in the CDCR at constant SGS (except for the SGS of 12.3 MPa). However, the UCS of grouted specimens for constant CDCR increased when the SGS increased; optimum solidification strengths for grouts between 19.3 and 23.0 MPa were obtained. The elastic moduli of the grouted specimens with different CDCR generally increased with increasing SGS, and the peak axial strain showed a slightly nonlinear decrease with increasing SGS. The supporting effect of the skeleton structure produced by the solidified grouts was increasingly obvious with increasing CDCR and SGS. The possible evolution of internal cracks for the grouted specimens was classified into three stages: (1) cracks initiating along the interfaces between the coal blocks and solidified grouts; (2) cracks initiating and propagating in coal blocks; and (3) cracks continually propagating successively in the interfaces, the coal blocks, and the solidified grouts near the coal blocks. Finally, after the propagation and coalescence of internal cracks through the entire specimens, there were two main failure modes for the failed grouted specimens. These modes included the inclined shear failure occurring in the more crushed coal rock and the splitting failure occurring in the less crushed coal rock. Both modes were different from the single failure mode along the fissure for the fractured coal rock after grouting solidification. However, compared to the brittle failure of intact coal rock, grouting into the different crushed degree coal rocks resulted in ductile deformation after the peak strength for the grouted specimens was attained.

• Explosives and Blasting
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• v.38 no.4
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• pp.26-36
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• 2020

With the increase of expansion and use of the underground space, the possibility of an underground explosion by terrorists is increasing. In this study, after modeling a circular tunnel excavated at a depth of 50m, an explosion load was applied to the inside of the tunnel. As for the explosion load, the explosion load of the maximum explosive amount for six types of vehicle booms proposed by ATF (Bureau of Alcohol, Tobacco, and Firearms) was calculated. For the rock mass around the circular tunnel, three types of rock grades were selected according to the support pattern suggested in the domestic tunnel design. Nonlinear dynamic analysis was performed to evaluate the influence of the ground structure by examining the surface displacement using the explosion load and rock mass characteristics as parameters. As a result of the analysis, for grade 1 rock, the influence on the uplift of the surface should be considered, and for grade 2 and 3 rocks, the influence on a differential settlement should be considered. In particular, for grade 3 rocks, detailed analysis is required for ground-structure interaction within 40m. Also, it is considered that the influence of Young's modulus is the main factor for the surface displacement.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.06a
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• pp.93-101
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• 2003

Steel frame-type retaining walls(SFRW) are constructed by on site bolting of prefabricated steel frames and internal filling of materials such as rocks with the size of 150-300mm. Easy & fast construction, superior drainage performance and structural performance to rigorous site conditions are some of the merits of applying the SFRW to various construction sites. After the development of the structural details, a test construction of SFRW, with the height of 6m and 30m in length, was carried out at an apartment site. After completion, several months of monitoring was carried out on the structure to check displacement, tilting, settlement, soil pressures and drainage characteristics. The results of the structural behavior of SFRW along with its construction methods are presented in the paper.

• The Journal of the Petrological Society of Korea
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• v.25 no.3
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• pp.211-230
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• 2016

Detailed mapping along the Keumwang fault reveals a complex history of multiple brittle reactivations following late Jurassic and early Cretaceous ductile shearing. The fault core consists of a 10~50 m thick fault gouge layer bounded by a 30~100 m thick damaged zone. The Pre-cambrian gneiss and Jurassic granite underwent at least six distinct stages of fault movements based on deformation environment, time and mechanism. Each stage characterized by fault kinematics and dynamics at different deformation environment. Stage 1 generated mylonite series along the Keumwang shear zone by sinistral ductile shearing during late Jurassic and early Cretaceous. Stage 2 was a mostly brittle event generating cataclasite series superimposed on the mylonite series of the Keumwang shear zone. The roundness of pophyroclastes and the amount of matrix increase from host rocks to ultracataclasite indicating stronger cataclastic flow toward the fault core. At stage 3, fault gouge layer superimposed on the cataclasite generated during stage 2 and the sedimentary basins (Umsung and Pungam) formed along the fault by sinistral strike-slip movement. Fragments of older cataclasite suspended in the fault gouge suggest extensive reworking of fault rocks at brittle deformation environments. At stage 4, systematic en-echelon folds, joints and faults were formed in the sedimentary basins by sinistral strike-slip reactivation of the Keumwang fault. Most of the shearing is accommodated by slip along foliations and on discrete shear surfaces, while shear deformation tends to be relatively uniformly distributed within the fault damage zone developed in the mudrocks in the sedimentary basins. Fine-grained andesitic rocks intruded during stage 4. Stage 5 dextral strike-slip activity produced shear planes and bands in the andesitic rocks. ESR(Electron Spin Resonance) dates of fault gouge show temporal clustering within active period and migrating along the strike of the Keumwang fault during the stage 6 at the Quaternary period.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.259-272
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• 2020

The seismic properties in the crust are affected by the lattice preferred orientation(LPO) of major minerals in the crust. Therefore, in order to understand the internal structure of the crust using seismic data, information on the LPO of the major constituent minerals and the seismic properties of major rocks in a specific region are needed. However, there is little research on the LPOs of minerals in the crust in Korea. In this study, we collected amphibolites from two outcrops in Wigokri, Gapyeong, located in the nothern portion of Gyeonggi Massif, and we measured the LPOs of major minerals of amphibolite, especially amphibole and plagioclase through EBSD analysis, and calculated seismic properties of amphibolite. Two types of LPOs of amphibole, which are defined as type I and type IV, were observed in the two outcrops of Gapyeong amphibolites, respectively. In the case of amphibolites with the type I LPO of amphibole, large seismic anisotropy of both P- and S-wave was observed, while in the amphibolites with the type IV LPO of amphibole, small seismic anisotropy was observed. This is consistent with previous experimental results. The polarization direction of the fast S-wave was aligned subparallel to the lineation regardless of the LPO types of amphibole. The seismic anisotropy observed in Gapyeong is expected to be helpful to interpret the structure and seismic data within the crust in Gyeonggi Massif.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.253-261
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• 2024

Olivine, a major mineral in the upper mantle with strong intrinsic elastic anisotropy, plays a crucial role in seismic anisotropy in the mantle, primarily through its lattice preferred orientation (LPO). Despite this, the influence of the microstructure of mylonitic rocks on seismic anisotropy remains inadequately understood. Notably, there is a current research gap concerning seismic anisotropy directly inferred from mylonitic peridotite massifs in Korea. In this study, we introduce the deformation microstructure and LPO of olivine in the mantle shear zone. We calculate the characteristics of seismic anisotropy based on the degree of deformation (proto-mylonite, mylonite, ultra-mylonite) and establish correlations between these characteristics. Our findings reveal that the seismic anisotropy resulting from the olivine LPO in the ultra-mylonitic rock appears to be the weakest, whereas the seismic anisotropy resulting from the olivine LPO in the proto-mylonitic rock appears to be the strongest. The results demonstrate a gradual decrease in seismic anisotropy as the fabric strength (J-index) of olivine LPO diminishes, irrespective of the specific pattern of olivine's LPO. Moreover, all samples exhibit a polarization direction of the fast S-wave aligned subparallel to the lineation. This suggests that seismic anisotropy originating from olivine in mylonitic peridotites is primarily influenced by fabric strength rather than LPO type. Considering these distinctive characteristics of seismic anisotropy is expected to facilitate comparisons and interpretations of the internal mantle structure and seismic data in the Yugu area, Gyeonggi Massif.