• Journal of the Korean GEO-environmental Society
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• v.10 no.3
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• pp.5-12
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• 2009

This study presents static and dynamic strength of coal ashes collected from disposal site of power plant. Main compositions of coal ashes were bottom ashes. In order to evaluate static and dynamic characteristics of coal ash, NGI direct-simple shear tests, cyclic simple shear tests and direct shear tests were conducted. The strengths of coal ashes from those tests were compared to those of sands. Bottom ashes among coal ashes used for this study were classified as sand from the grain size distribution and show higher strength properties than the sands. For utilization of coal ashes in civil engineering project, mixing coal ashes with sandy soil using batch plant is inconvenient and the cost is higher than the spreading sand layer and coal layer alternately. In order to simulate both mixing type and layered type construction, sands and coal ashes were mixed with volume ratio 50:50 and prepared sand and coal ash layers alternately with the same volume ratio. From the tests mixed coal ashes-specimen shows slightly higher static and cyclic strength than the layered specimen at the same density. The higher strength seems due to the angular grain of bottom ashes. The cyclic stress ratio at liquefaction decreases rapidly as the number of cycle increases at mixed specimen than that of layered specimen.

• Journal of the Korean Wood Science and Technology
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• v.10 no.3
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• pp.166-166
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• 1982

This study has been made to make an observation regarding present status of the coal mine props which is desperately needed for coal production, despite of great shortage of the timber resources in this country, and investigate the effects of diffusion process on the decay resistances of the mine props as applied preservatives of Malenit and chromated zinc chloride. The results are as follows. 1. Present status of the coal mine props Total demand of coal mine props in the year of 1975 was approximately 456 thousand cubic meters. The main species used for mine props are conifer (mainly Pinus densiflora) and hardwood (mainly Quercus). Portions between them are half and half. With non fixed specification, wide varieties of timber in size and form are used. And volume of wood used per ton of coal production shows also wide range from 0.017 cubic meter to 0.03 cubic meter. 2. Decay resistance test a) The oven dry weight decreased between untreated specimen and treated specimen has not shown any significantly, although it has shown some differences in average values between them. It may be caused by the shorter length of the test. b) The strength of compression test between untreated specimen and treated specimen has also shown the same results as shown in case of weight decrease. Reasons assumed are the same. c) The amounts of the extractives in one percent of sodium hydroxide (NaOH) between untreated and treated specimen have shown the large value in case of untreated specimen than that of treated. 3. The economical benifit between untreated and treated wood when applied in field has seen better in long tenn base in case of treated wood, although the primary cost of treated wood add a little bit more cost than that of the untreated wood.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.137-145
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• 2004

Limestone zone in korea have been distributed to diagonal line so that it is wide from the Gangwondo to the Jeonlanamdo. The limestone cavity and fractured zone were formed by chemical weathering. Limestone cavity and fractured zone was reinforced with cemented milk(w/c=60%)by high pressure jet grouting by tripple -pipe to establish bridge foundation on the ground condition like limestone cavity. To analyze property of limestone and solid of cement milk(w/c=65%), mixed solid of cement, core NX size in the limestone cavity and fractured zone and compressive strength. Seismic tomograpy exploration was pcrforn1cd to analyze deformation modulus of limestone. The analysis suggests that deformation modulus of limestone has effect on uniaxial compressive strength, seismic velocity, seismic elasticity modulus. Average static elasticity modulus of limestone is $5.08{\times}10^5kgf/cm^2$, cement and coal mixed solid is $0.25{\times}10^5kgf/cm^2$, $0.095{\times}10^5kgf/cm^2$. Average seismic velocity of limestone is 5.240m/sec, cement and coal mixed solid is 2,211.3m/sec, 1,447.5m/sec. Average uniaxial compressive strength of limestone was $1,221.3kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $125.22kgf/cm^2$, $35kgf/cm^2$ each other. Average friction angle of limestone was $49.14^{\circ}$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $38.39^{\circ}, 25.83^{\circ}$ each other. Average cohesion of limestone was $137.7kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $23.5kgf/cm^2$, $15.5kgf/cm^2$ each other. Average deformation modulus of limestone was $2.84{\times}10^5kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $0.4{\times}10^5kgf/cm^2, 0.12{\times}10^5kgf/cm^2$ each other. It was analyzed that the elasticity and uniaxial compressive strength, seismic velocity of solid of cement milk mixed limestone pieces and coal had an highly interrelation regardless of existence of limestones pieces and coal but it had shown that limestones had an lower interrelation. In case of field seismic velocity and deformation of limestone, SIC solid of cement milk mixed with coal and limestone pieces had an highly interrelation.

• Resources Recycling
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• v.14 no.4 s.66
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• pp.3-9
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• 2005

In this study, the utilization possibility of coal-preparation refuse emitted from Hwasun coal mine in Korea as a raw material for ceramic body was investigated. The firing shrinkage ratio of ceramic specimen made from the coal-preparation refuse was reduced with increasing the addition amounts of that, while the compressive strength was slightly decreased. The weight of ceramic body was also reduced because carbon contained in the coal-preparation refuse was burn by fring. The water adsorption ratio of the ceramic specimen was under 10 wt%, and the compressive strength of that was over 21 MPa at over $1,150^{\circ}C$ for 2 hr. Therefore, it was possible to make the 1st garde clay brick of KS L 4201 from the coal-preparation refuse.

• Clean Technology
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• v.19 no.4
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• pp.464-468
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• 2013

In this study, in order to increase solid content of coal water fuel (CWF), various experimental parameters (i.e., coal type, additive, particle size distribution, drying method) were evaluated. To investigate the drying method, specimen is compared to using flash dry, fluidized bed dry and oil deposit stabilized coal. Difference of the solid content between low rank coal and high rank coal in this case indicate that high rank coal exhibits more higher than 20% of the solid cotent. And specimen for dispersibility was prepared by using dispersing agent of 4 types. As a result, using the dispersing agent was shown 5% higher in sold content than the case of not using the dispersing agent. Efficiency of CWF was improved by using fine coal of 80% in the particle size distribution of coal. Result of CWF using drying methods of 3 types, oil deposit stabilized (ODS) coal dried and stabilized was effective 12% higher in sold content than raw coal.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.85-95
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• 2018

Water affects the mechanical properties of coal and stress wave propagation. To comprehensively investigate the effect of water content on the properties of coal, laboratory tests including X-Ray Diffraction (XRD) analysis, P-wave test, S-wave test, static and dynamic compression test with different water contents were conducted. The compressive strength, elastic modulus and failure strain and their mechanism of coal specimen under coupled static-dynamic load with the increased water content were observed. Meanwhile, energy transmission and dissipation characteristics of a stress wave in coal specimens with different water contents under dynamic load and its relation with the failure features, such as fragmentation and fractal dimension, of coal was analyzed. Furthermore, the dynamic interpretation of water infusion to prevent coal burst based on water infusion model of coal seam roadway was provided.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.3
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• pp.147-152
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• 2010

In this study, the artificial coarse aggregate was manufactured by using coal ash and low grade clay. The characteristics of a coal ash-clay system were investigated using XRD, XRF, TG-DTA, SEM and Dilatometer with various coal ash contents. The chemical compositions are the fly ash, bottom ash and clay, $Al_2O_3$ are 28.5 wt%, 32.4 wt% and 18.1 wt%, and $SiO_2$ are 33.0 wt%, 53.7 wt% and 68.4 wt% in weight ratio, respectively. The shrinkage of specimens started at around $850^{\circ}C$ and changed little up to $1100^{\circ}C$, but increased markedly at above $1100^{\circ}C$. The shrinkage rate is strongly related to the decarbonization amount of coal ash. At the sintering temperature $1150^{\circ}C$, it was found that quartz, mullite, anorthite and albite phase exist in all specimens. It was found that bottom-clay system specimen sintered at $1150^{\circ}C$ had a good compressive strength of 87.5 kg/$cm^2$, and the compressive strength of bottom-clay specimen was higher than that of fly-clay system specimen. The reusability of coal ash as a raw material in the process of shotcrete resources such as artifical coarse aggregate is highly expected.

• Geomechanics and Engineering
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• v.20 no.1
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• pp.55-66
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• 2020

The damage or failure of coal rock is accompanied by energy accumulation, dissipation and release. It is crucial to study the energy evolution characteristics of coal rock for rock mechanics and mining engineering applications. In this paper, coal specimens sourced from the Xinhe mine located in the Jining mining area of China were initially subjected to uniaxial compression, and the micro-parameters of the two-dimensional particle flow code (PFC^2D) model were calibrated according to the experimental test results. Then, the PFC^2D model was used to subject the specimens to substantial uniaxial compression, and the energy evolution laws of coal specimens with various schemes were presented. Finally, the elastic energy storage ratio m was investigated for coal rock, which described the energy conversion in coal specimens with various arrangements of preformed holes. The arrangement of the preformed holes significantly influenced the characteristics of the crack initiation stress and energy in the prepeak stage, whereas the characteristics of the cumulative crack number, failure pattern and elastic strain energy during the loading process were similar. Additionally, the arrangement of the preformed holes altered the proportion of elastic strain energy U_e in the total energy in the prepeak stage, and the probability of rock bursts can be qualitatively predicted.

• Structural Engineering and Mechanics
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• v.80 no.5
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• pp.523-538
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• 2021

The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution numerical models, namely surface-wetting model, core-wetting model and uniform-wetting model, were established to explore the water distribution influences. The feasibility and validity of the surface-wetting model were further demonstrated by comparing the simulation results with laboratory results. The investigation reveals that coal mechanical properties are affected by both water saturation coefficient and water distribution condition. For all water distribution models, micro-cracks always initiate and nucleate in the water-rich area and thus lead to distinct macro fracture characteristics. With the increase of water saturation coefficient, the failure of coal tends to be less violent with less cracks and ejected fragments. In addition, the core-wetting specimen is more sensitive to water than specimens with other water distribution models.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.145-151
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• 1991

The final purpose of this study is to examine the uses of coal ash, by-product from thermal power plant as a type of filling-embankment materials and the reuses of ash ponds. In this time, to investigate the dynamic properties, we made the test piece specimen with coal ashes, and obtained the damping ratio. In place(ash pond), the damping property by underground wall was investigated before and after soil improvements. The damping ratio of coal ash test piece specimen of 12% cement is the highest and that of 9% cement or chemical grout, that of 6% cement is in order. In same coal ash test piece, the damping ratio increases with decreasing the void ratio. In conclusion, it could be said that the damping ratio increases with the stiffness of materials. In the ash pond, the damping effect is the most when trench is set through the vibration wave propagation course, and when soil is improved the higher stiffness of the improved soil is, the more damping effect appeared. It is justified to obtain not only the dropping of permeability and the strength increase, but also the damping effect fairly by soil improvements.