• Geomechanics and Engineering
• /
• v.12 no.3
• /
• pp.541-560
• /
• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.33 no.2
• /
• pp.244-252
• /
• 2006

The aims of this study were to determine if flowable composites can be used as pit and fissure sealants without bonding agents. Three flowable composites(Filtek Flow, Tetric Flow, Charmfil Flow) and a filled sealant (Ultraseal XT plus) were used. The pattern of resin tag formation in the four sealant materials were compared using SEM. For the microleakage assessment, 54 extracted human premolar teeth were randomly divided into 3 groups containing 18 premolars each. In each group, a conventional filled sealant and one of the three flowable composites were applied to occlusal fissures. The teeth were thermocycled(1200 cycles between $5^{\circ}{\pm}2^{\circ}C\;and\;55^{\circ}{\pm}2^{\circ}C$ with a dwell time of 30 seconds) and immersed in a 1% methylene blue solution for 48 hours. Each tooth was sectioned and examined to determine the extent of dye penetration. Three flowable composites and a filed sealant showed a similar resin tag formation pattern. The three flowable composites showed significantly more microleakage in each group than the filled sealant. The level of microleakage was similar in the three flowable composites. Flowable composites are not recommended as pit and fissure sealants because more microleakage can occur even when occlural fissures are mechanically widened.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.32 no.3
• /
• pp.491-498
• /
• 2005

Occlusal fissures and pits are ideal places for the development of caries. Pit and fissure sealants are now considered as a very effective means to prevent dental caries. The purpose of this investigation was to examine the effect on the sealant penetration of the elapse of time from the application of sealant until exposure to visible light, and to examine the effect of the filler content and tooth position on the sealant penetration. 192 extracted human premolars were used to this experiment. Following enamel conditioning, a light-polymerized sealant was applied and 4 different periods of time(3, 5, 10, 20 seconds) were allowed until exposure to the light source. The results obtained were as follows; 1. According to time, in both unfilled sealant and filled sealant penetration increases deeply through mindfulness. 2. Sealant that apply to mandiblar premolar penetrated deeply through than to maxillay teeth. 3. Penetration difference according to filler content, unfilled sealant penetrated deeply through than filled sealant. The result from this study indicated that unfilled sealant penetrated most deeply in mandible when at least 20s time elapsed.

• Journal of the Mineralogical Society of Korea
• /
• v.17 no.3
• /
• pp.189-199
• /
• 2004

Cretaceous sedimentary rocks bearing dinosaur tracks in the Goseong interchange area were studied for their conservation and public display in the aspect of applied mineralogy. Black clay layers alternate with silt layers in the sedimentary rocks. The verical and horizontal fissures are commonly filled with calcite veinlets, supergenetic iron and manganese oxides. The rocks are composed of quartz, albite, K-feldspar, calcite, chlorite, illite, muscovite, and biotite, with minor apatite and rutile. Silt layers are relatively rich in calcite and albite, whereas clay layers are abundant in quartz, illite, and chlorite. Al, Fe, Mg, K, Ti, and P are enriched in the clay layers, while Ca, Na, and Mn in silt. Most of trace elements including V, Cr, Co, Ni, Cs, Zr, REE, Th, and U are enriched in clay layers. Inorganic carbon are present in silt layers as calcite, while organic carbon in black clay layers. The black clay layers were partly altered to yellow clay layers along the fissures, simultaneously with the decrease of organic carbon. Selective exfoliation of clay-rich black and yellow clay layers, calcite matrix of silt layers and calcite infillings of fissures are estimated as the major weakness potentially promoting chemical and physical degradation of the track-bearing rock specimens.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.3
• /
• pp.504-511
• /
• 2001

Preventive resin restoration, extended concept of occlusal pit and fissure sealing, is procedure composed of as follows. Cavity preparation is limited to areas of initial caries The cavity is then restored with composite resin, while other sound pits and fissures are sealed with pit and fissure sealant. If pit and assure sealant with which microrestoration is possible is used, it may be of great benefit to both patient and operator in case of difficult-to-control children s treatment. However study on preventive resin restoration using this kind of materials have been scarce. The purpose of this study was to compare the microleakage of four different modes of preventive resin restoration. Restoration using only composite resin was compared together Fifty-five bicuspids were prepared with small class I cavity preparation on the occlusal surface, divided into the following groups and restored accordingly. Group 1 : Cavity was restored with Z-100 composite resin Group 2 : Cavity was restored with Z-100 composite resin. Pits and fissures were then sealed with Teethmate F-1 Group 3 : Cavity was restored with Z-100 composite resin Pits and fissures were then sealed with Ultraseal XT-plus Group 4 : Cavity and pits and fissures were restored with Ultraseal XT-plus altogrether Group 5 : Cavity was restored with Ultraseal XT-plus. Pits and fissures were then sealed with the same material. After restoration, the samples were thermocycled 500 times between $5^{\circ}C$ and $55^{\circ}C$ with a dwell time of 30 seconds. After thermocycling, the samples were dipped into 1% methylene blue solution for 24 hours, then rinsed with tap water. The teeth were then embedded in resin and cut buccolingually along the tooth axis and observed with a stereomicroscope to determine the degree of microleakage. The results were as follows : 1. Group 4 showed the greatest microleakage, while group 3, showed the least. The mean microleakage decreased in the following order:4>1>5>2>3. 2. There was no stastically significant difference between group 1 and group 5(p>0.05). However, group 1 showed significantly greater microleakage compared to group 2 and 3(p<0.05) Group 1 showed significantly less microleakage compared to group 4(p<0.05). 3. Group 2 showed no statistically significant difference compared to group 3(p>0.05). However group 2 showed significantly less microleakage compared to group 4 and 5(p<0.05) 4. Group 3 showed significantly less microleakage compared to group 4 and 5(p<0.05). 5. Group 5 showed significantly less microleakage than group 4(p<0.05).

• Economic and Environmental Geology
• /
• v.31 no.1
• /
• pp.1-10
• /
• 1998

Copper mineralization of the Donghwa and Hwanghagsan mines was deposited in hydrothermal quartz veins which filled fissures in Cretacous sedimentary rocks. Ore minerals are pyrite, sphalerite, chalcopyrite, bornite, galena, wittichenite and unidentified Cu-Bi-Pb-Sb-S mineral. On the basis of salinities and homogenization temperatures for fluid inclusions, the Donghwa deposit was deposited from $300^{\circ}C$ to $220^{\circ}C$ with 2.5 to 0.2 wt.% eq. NaCl, and the Hwanghagsan deposits was deposited from $300^{\circ}C$ to $160^{\circ}C$ with 4.0 to 0.0 wt.% eq. NaCl. Evidence of boiling suggests pressure of 170 to 60 bar, these pressures correspond to 1700 m to 600 m. The ${\delta}^{34}S_{H_2S}$ values of the Donghwa deposit (4.8~7.4%) are higher than those of the Hwanghagsan deposit (3.5~4.5%), sulfur isotope compositions indicate that ore fluids partially reacted with meteoric water and wall-rock. Equilibrium thermodynamic interpretation indicates that the temperature versus $fs_2$ of the Donghwa deposit (> $420^{\circ}C$, $10^{-3.2}atm$) is higher condition than that of the Hwanghagsan deposit (> $290^{\circ}C$, $10^{-7.0}atm$). K-Ar ages for biotite granite and quartz porphyry in the study area are 64.7 Ma, and 60.9 Ma, reapectively. Mineralization age using sericite in the Donghwa deposits is 59.8 Ma. Therfore, Copper mineralization in the study area was associated with acidic igneous activity such as biotite granite or quartz porphyry.

• Economic and Environmental Geology
• /
• v.24 no.2
• /
• pp.151-165
• /
• 1991

The Au-Ag deposits of the Euiseong area occurred in quartz veins which filled fissures in Cretaceous sedimentary and volcanic rocks. These ore veins can be classified in two types of deposits based on metallic mineral assemblages as follow: a pyrite type gold-silver deposit (Hoedong mine), characterized by Cu sulfides with Au-Ag alloy, and a Sb-rich silver deposit (Keumdongdo mine), characterized by base metal with Ag-bearing sulfosalts. Mineralogic and fluid inclusion evidences suggest that the ore minerals of these deposits was deposited from initial high temperatures (near $350^{\circ}C$) to later lower temperatures ($200^{\circ}C$) with moderate salinity fluids ranging from 5.8 to 3.8 eq. wt. % NaCl. The gold-silver mineralization of the Hoedong mine occurred at temperatures between 300 and $200^{\circ}C$ from fluids with log $f_{s_2}$ of -10 ~ -16 atm. The antimony - silver mineralization of the Keumdongdo mine were deposited at the higher temperatures (350 to $250^{\circ}C$) and $f_{S_2}$ (-10 ~ -13 atm) than gold mineralization of the Hoedong mine. The calculated log f02 of fluids at $250^{\circ}C$ in two deposits are -32 to -34 atm and -36.5 to -38.5 atm, respectively. Boiling evidences indicate that the ore mineralization of the Hoedong mine occurred at more shallow depth (0.5km) than that (1km) of the Keumdongdo mine. The above differences of depositional environments between two deposits caused the compositional changes of ore minerals such as electrum and sphalerite.

• Journal of the Korean earth science society
• /
• v.29 no.7
• /
• pp.551-558
• /
• 2008

The Soowang deposits occur in the quartz veins that were filled fissures in the middle Cretaceous porphyritic granite and/or the Precambrian Sobaegsan gneiss complex. Paragenetic studies suggest that the vein filling can be divided into four identifiable stages. Sphalerites were deposited by the cooling fluids at stages I, II, and III. The results of microscopic observation and EPMA analysis suggest that the chalcopyrite dots and disease in sphalerite are replacement products by later hydrothermal solution at the early stage III. The inferred processes of chalcopyrite disease are as follows: (1) Fe enrichment to the margins and along the cracks of the Fe-poor sphalerite by Fe-rich solution, (2) Formation of chalcopyrite dots in the Fe-enriched sphalerite formed at the stage II, and Fe reduction of sphalerite near the chalcopyrite dots by Cu-bearing solution, (3) Formation of "chalcopyrite disease" penetrating the compositional zoning of sphalerite at the early stage III.

• Economic and Environmental Geology
• /
• v.43 no.2
• /
• pp.137-148
• /
• 2010

The Myoungbong mine located in Boseong-gun, Jellanamdo consists of Au-Ag bearing quartz veins which filled the fissures of Bulguksa granitic rocks of Cretaceous. The tailings obtained from the Myungbong mine were used to investigate the effects of various processes, such as oxidation of primary sulfides and formation(alteration) of secondary and/or tertiary minerals, on arsenic immobilization in tailings. This study was conducted via both mineralogical and chemical methods. Mineralogical methods used included gravity and magnetic separation, ultrasonic cleaning, and instrumental analyses(X-ray diffractometry, energy-dispersive spectroscopy, and electron probe microanalyzer) and aqua regia extraction technique for soils was applied to determine the elemental concentrations in the tailings. Iron (oxy)hydroxides formed as a result of oxidation of tailings were identified as three specific forms. The first form filled in rims and fissures of primary pyrites. The second one precipitated and coated the surfaces of gangue minerals and the final form was altered into yukonites. Initially, large amounts of acid-generating minerals, such as pyrite and arsenopyrite, might make the rapid progress of oxidation reactions, and lots of secondary minerals including iron (oxy)hydroxides and scorodite were formed. The rate of pH decrease in tailings diminished, in addition, as the exposure time of tailings to oxidation environments was prolonged and the acid-generating minerals were depleted. Rather, it is speculated that the pH of tailings increased, as the contribution of pH neutralization reactions by calcite contained in surrounding parental rocks became larger. The stability of secondary minerals, such as scorodite, were deteriorated due to the increase in pH, and finally arsenic might be leached out. Subsequently, calcimn and arsenic ions dissociated from calcites and scorodites were locally concentrated, and yukonite could be grown tertiarily. It is confirmed that this tertiary yukonite which is one of arsenate minerals and contains arsenic in high level plays a crucial role in immobilizing arsenic in tailings. In addition to immobilization of arsenic in yukonites, the results indicate that a huge amount of iron (oxy)hydroxides formed by weathering of pyrite which is one of typical primary minerals in tailings can strongly control arsenic behavior as well. Consequently, this study elucidates that through a sequence of various processes, arsenic which was leached out as a result of weathering of primary minerals, such as arsenopyrite, and/or redissolved from secondary minerals, such as scorodite, might be immobilized by various sorption reactions including adsorption, coprecipiation, and absorption.

• Journal of the Korean earth science society
• /
• v.25 no.6
• /
• pp.484-494
• /
• 2004

The Soowang Au-Ag deposits occur as quartz veins which filled fissures in middle Cretaceous porphyritic granite an/or gneiss of the Precambrian Sobaegsan gneiss complex. The paragenetic studies suggest that vein filling can be divided into four identifiable stages (I to IV). Stage I is the main sulfide stage, characterized by the deposition of base-metal sulfide and minor electrum. Stage II is the electrum stage, whereas stage III represents a period of the deposition of silver-bearing sulfosalts and minor electrum. Stage IV is the post ore stage. Mineralogical and fluid inclusion evidences suggest that mineralization of the Soowang deposits were deposited by the cooling of the fluids from initial high temperatures 300$^{\circ}C$ to later low temperatures 150$^{\circ}C$. The salinity of the fluids were moderate, ranging from 10.4wt.% equivalent NaCl in sphalerite to 3.1wt.% equivalent NaCl in barite. The gold-silver mineralization of the Soowang mine occurred at temperatures between 140 and 250$^{\circ}C$ from fluids with log $fs_2$ from -12 to -18 atm. A consideration of the pressure regime during ore deposition, based on the fluid inclusion evidence of boiling, suggests lithostatic pressure of less than 210 bars. This pressure condition indicates that vein system of the Soowang deposit formed at depth around 800 m below the surface at the time of gold-silver mineralization.