• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.15-29
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• 2010

Spalling is a kind of instability phenomenon of surrounding rock around underground openings subjected to high in-situ stress according to the development of extension fractures. Three kinds of spalling criteria have been presented so far; however, all spalling criteria have the range of values so that the fuzziness and vagueness of spalling criterion cannot be avoided. In this study, a new fuzzy probability model is proposed to predict the probability of spalling in a systematic way by using fuzzy probability theory. Many of the underground opening projects worldwide are evaluated with the proposed method. Prediction results expressed as the spalling probability agree well with the in-situ observations. In particular, a new fuzzy probability model considering all three evaluation indices of spalling by adopting weighting factors based on relative reliability among three evaluation indices is able to resolve erroneous prediction of spalling by choosing only one prediction method. Moreover, the more reasonable value of spalling probability could have been obtained by adopting the modified damage index to the newly proposed fuzzy probability model.

• Economic and Environmental Geology
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• v.45 no.1
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• pp.31-40
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• 2012

This paper examined the characteristics of ductile and brittle structural elements with detailed mapping by lithofacies classification to clarify the relationship between the geological structure and the geochemical high-grade uranium anormal zone and to provide the basic information on the flow of groundwater in the eastern area of Shinbo mine, Jinan-gun, Jeollabuk-do, Korea. It indicates that this area is mainly composed of Precambrian quartzite, metapelite, metapsammite, which show a zonal distribution of mainly ENE-WSW trend, and age unknown pegmatite and Cretaceous porphyry which intrude them. But the Cretaceous Jinan Group which unconformably covers them, contrary to assumption, could not be observed. The main ductile deformation structures of Precambrian metasedimentary rocks were formed at least through three phases of deformation [ENE striking regional foliation (D1) -> ENE or EW striking crenulation foliation (D2) -> WNW or EW trending open, tight, kink folds (D3)]. The predominant orientation of S1 regional foliation strikes ENE and dips south, being similar to the zonal distribution of Precambrian metasedimentary rocks. Most predominant orientation of high-angled brittle fracture (dip angle ${\geq}45^{\circ}$) [ENE (frequency: 24.3%) > NS (23.9%) > (N)NW (18.8%) > WNW (16.9%) > NE (16.1%) fracture sets in descending frequency order], which is closely related to the flow of groundwater, strikes ENE and dips south. It also agrees with the zonal distribution of metasedimentary rocks and the predominant orientation of S1 regional foliation. The next one strikes NS and dips east or west. Considering the controlling factor of the geochemical uranium anormal zone in the Shinbo mine and its eastern areas from the above structural data. the uranium source rock in these areas might be pegmatite and the geochemical uranium anormal zone in the Sinbo mine area could be formed by an secondary enrichment through the flow of pegmatite aquifer's groundwater into the Sinbo mine area like the previous research's result.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.489-500
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• 2017

It is not rare that pseudotachylite, dark colored rock with glassy texture, is recognizable in deep core samples drilled up to 900 m from the surface. Pseudotachylite with widths varying few to 20 cm is sharply contacted or interlayered with the host rocks composed of Jurassic granite and Precambrian amphibolite gneiss, showing moderately ductile deformation or slight folding. Pseudotachylite occurring at varying depths in the deep drill core are slightly different in texture and thickness. There is evidence of fault gouge at shallower depths, although brittle deformation is pervasive in most drill cores and pseudotachylite is identified at random depth intervals. Under scanning electron microscope (SEM), it is evident that the surface of pseudotachylite is characterized by a smooth, glassy matrix even at micrometer scale and there is little residual fragments in the glass matrix except microcrystals of quartz with embayed shape. Such textural evidence strongly supports the idea that the pseudotachylite was generated through the friction melting related to strong seismic events. Based on X-ray diffraction (XRD) quantitative analysis, it consists of primary minerals such as quartz, feldspars, biotite, amphibole and secondary minerals including clay minerals, calcite and glassy materials. Such mineralogical features of fractured materials including pseudotachylite indicate that the fractured zone might form at low temperatures possibly below $300^{\circ}C$, which implies that the seismic activity related to the formation of pseudotachylite took place at shallow depths, possibly at most 10 km. Identification and characterization of pseudotachylite provide insight into a better understanding of the paleoseismic activity of deep grounds and fundamental information on the stability of candidate disposal sites for high-level radioactive waste.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.1-14
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• 2010

Until now, the evaluation method of spalling depth using Martin et al. (1999)'s linear regression relations has long been known applicable. However, it is not likely that the proposed equation is applicable to the openings other than circular type and mostly overpredict the spalling depth in comparison with actual spalling cases. Moreover, the evaluation method to estimate the spalling width has not been presented yet; it is essential to evaluate the spalling width in addition to the spalling depth, because the shape of the spalled region influences the choice of suitable rock reinforcement. In this study, linear regression equations, in which normalized spalling depth ($d_f/W_D$) and normalized spalling width ($w_f/W_D$) are functions of three spalling evaluation indices, ${\sigma}_1/{\sigma}_c,\;D_{is}(={\sigma}_{max}/{\sigma}_c)$ and ${\sigma}_{dev}/{\sigma}_{cm}$, are established based on in-situ spalling observations and CWFS simulation results. Confidence intervals of 95% using the statistical inference theory are used in verifying the reliability of linear regression equations. Spalling depth ($d_f$) and spalling width ($w_f$) predicted from the proposed linear regression relations, which take three spalling evaluation indices into account, showed reasonable match with in-situ observations by adopting weighting factors considering the degree of variance of linear regression relations.

• The Journal of the Petrological Society of Korea
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• v.28 no.3
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• pp.157-169
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• 2019

Pseudotachylytes, produced by frictional heating during seismic slip, provide information that is critical to understanding the physics of earthquakes. We report the results of occurrence, structural characteristics, scanning electron microscopic observation and geochemical analysis of pseudotachylytes, which is presumed to have formed after the Late Cretaceous in outcrops of the Paleoproterozoic granitic gneiss on the Bulil waterfall of the Jirisan area, Yeongnam massif, Korea. Fault rocks, which are the products of brittle deformation under the same shear stress regime in the study area, are classified as pseudotachylyte and foliated cataclasite. The occurrences of pseudotachylyte identified on the basis of thickness and morphology are fault vein-type and injection vein-type pseudotachylyte. A number of fault vein-type pseudotachylytes occur as thin (as thick as 2 cm) layers generated on the fault plane, and are cutting general foliation and sheared foliation developed in granitic gneiss. Smaller injection vein-type pseudotachylytes are found along the fault vein-type pseudotachylytes, and appear in a variety of shapes based on field occurrence and vein geometry. At a first glance fault vein-type seudotachylyte looks like a mafic vein, but it has a chemical composition almost identical to the wall rock of granitic gneiss. Also, it has many subrounded clasts which consist predominantly of quartz, feldspar, biotite and secondary minerals including clay minerals, calcite and glassy materials. Embayed clasts, phenocryst with reaction rim, oxide droplets, amygdules, and flow structures are also observed. All of these evidences indicate the pseudotachylyte formed due to frictional melting of the wall rock minerals during fault slip related to strong seismic faulting events in the shallow depth of low temperature-low pressure. Further studies will be conducted to determine the age and mechanical aspect of the pseudotachylyte formation.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.31-49
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• 2010

Nearly NS-trending Fe-Ti ore bodies intermittently occur in the Hadong anorthosites, south Korea, irrespective of the rock types of the anorthosites. In order to determine their occurrence mode and deformation history, we collected the features of occurrence and geological structures in the field, petrographic features using thin sections of the principal constituent rocks, and geochemical data of ilmenites in the ore body using electron probe microanalysis. Fe-Ti ore bodies examined in this study are divided into two types: dike- and lamina-types. It is steadily supported that the dike-type has intruded into the anorthositic rocks after their emplacement and solidification. And the laminar-type is probably a result of the mylonitization and transposition of the dike-type ore bodies parallel to the shear planes, due to later strong dextral ductile shearing. In the meantime, the Fe-Ti ore bodies have experienced the stronger dextral shearing in the more northern part of the study area, i.e. Cheongryong-ri, Wolhoeng-ri, Jonghwa-ri, and Jayangri and Baekun-ri in ascending order of its strength, together with the less content of $TiO_2$. All ilmenites of the ore bodies have very similar chemical composition, as pure ilmenite of 52~55 wt.% in $TiO_2$ content, irrespective of the occurrence mode and degree of later ductile shearing of the ore bodies. And they didn't experience to exsolve into magnetite. The structural data indicate that the Hadong anorthosites have deformed by NNE-trending folding, intrusion of the Fe-Ti ore bodies, NNW~NNE-trending dextral ductile shearing, NW~NNW-trending sinistral semi-brittle shearing, and intrusion of NNE~NE-trending mafic dykes in descending order of chronology after the formation of foliation of the anorthositic rocks. The foliation is interpreted as a result of the accumulation of crystals that settle out from the magma by the action of gravity.