• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.841-844
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• 2006

Recently, tunnels being constructed in korea with the increased construction of highways, high-speed railways and hydro structure. shotcrete and spray is one of the major processes in that construction. So general Shotcrete and spray has many problems on strength property, environmental pollution and human body noxiousness as the use of accelerater. However, In this paper using HES-LMS(High Early Strength Latex Modified Spray) without accelerater can solve problems which are mentioned above. problems that the hish early cement has can be solved by modifying material with latex. Therefore HES-LMS mortar is Classify by High performance and High ability. Analysis according to the variables such as W/C, Latex content and sand content is conducted. Studied about mechanical characteristic of material such as each parameter characteristic, and rebound characteristic is completed.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.332-341
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• 2010

Standard dimensionless parameters cannot simultaneously represent all operation modes of a pump-turbine. They either have singularities at E=0 and multiple values in the 'unstable' areas, or else get singular at n=0. P. Suter (1966) introduced an alternative set of variables which avoids singularity and always remains unique-valued. This works for non-regulated pumps but not so well for regulated machines. A modification by C.S. Martin avoids distortion at low load. The present paper describes further improvements for the representation of torque, and for closed gate (where Suter's concept does not work). The possibility to interpolate across all operation modes is likewise useful for representing other mechanical parameters of the machine. Practical application for guide vane torque and pressure pulsation data is demonstrated by examples.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.193-194
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• 2005

By the high-temperature pad conditioning process: The slurry residues in pores and grooves of the polishing pad were clearly removed. These clear pores and enlarged grooves made the slurry attack the oxide surface. The changed slurry properties by high-temperature pad conditioning process made the oxide surface hydro-carbonate to be removed easily.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.1041-1048
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• 2021

An engineered barrier system (EBS) for the disposal of high-level radioactive waste (HLW) is composed of a disposal canister with spent fuel, a buffer material, a gap-filling material, and a backfill material. As the buffer is located in the empty space between the disposal canisters and the surrounding rock mass, it prevents the inflow of groundwater and retards the spill of radionuclides from the disposal canister. Due to the fact that the buffer gradually becomes saturated over a long time period, it is especially important to investigate its thermal-hydro-mechanical-chemical (THMC) properties considering variations of saturated condition. Therefore, this paper suggests a new method of measuring thermal conductivity and water suction for single compacted bentonite at various levels of saturation. This paper also highlights a convenient method of saturating compacted bentonite. The proposed method was verified with a previous method by comparing thermal conductivity and water suction with respect to water content. The relative error between the thermal conductivity and water suction values obtained through the proposed method and the previous method was determined as within 5% for compacted bentonite with a given water content.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.41-48
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• 2016

This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.409-415
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• 2016

In this study, we test the effects of the surface roughness on the hydro efficiency of double-suction centrifugal pumps ($Q=70.7m^3/min$, H = 87 m). The original surface of the impeller and inner casing were coated, resulting in surface-roughness reductions ranging from $100{\sim}110{\mu}m$ to $0{\sim}0.08{\mu}m$. We conducted experimental studies to measure the efficiency of the pumps and operating-pump electro energy variations with different surface roughness values. The experimental results showed that the efficiency of the pumps increased by about 0.8~1.79% and the electric energy of the operating pump was reduced by around 4.38 ~ 6.08%. These results indicate that the performance of the pumps depend largely on the surface roughness of the impeller and inner casing, and by reducing the surface roughness, we can improve the efficiency of the pump and reduce costs by reducing the electric energy consumption.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.199-213
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• 2017

Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete model could be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid- and long- term chloride ingress assessment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.419-434
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• 2020

In this study, the damage parameters of Mazars model for KURT (KAERI Underground Research Tunnel) granite are measured form uniaxial compressive and Brazilian tests under the simulated coupled condition of a deep geological disposal. The tests are conducted in three different temperatures (15℃, 45℃, and 75℃) and dry/saturated conditions. Major model parameters such as maximum effective tensile strain (𝜖_d0), A_t, B_t, A_c, and B_c differ from the typical reference values of concrete specimens. This is likely due to the difference in elastic modulus between rock and concrete. It is found that the saturation of specimens causes an increase in value of B_t and B_c while, the rise in temperature increases 𝜖_d0 and B_t and decreases B_c. The damage model obtained from this study will be used as the primary input parameters in the development of coupled Thermo-Hydro-Mechanical Damage numerical model in KAERI.

• Explosives and Blasting
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• v.26 no.2
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• pp.11-19
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• 2008

The development of an excavation damaged zone, EDZ, due to the blasting impact and stress redistribution after excavation, can influence on the long tenn stability, economy, and safety of the underground excavation. In this study, the size and characteristics of an EDZ around an underground research tunnel, which was excavated by controlled blasting, in KAERI were investigated. The results were implemented into the modelling for evaluating the influence of an EDZ on hydro-mechanical behavior of the tunnel. From in situ tests at KURT, it was possible to determine that the size of EDZ was about l.5rn. Goodman jack tests and laboratory tests showed that the rock properties in the EDZ were changed about 50% compared to the rock properties before blasting. The size and property change in the EDZ were implemented to a hydro-mechanical coupling analysis. In the modeling, rock strengths and elastic modulus were assumed to be decreased 50% and. the hydraulic conductivity was increased 1 order. From the analysis, it was possible to see that the displacement was increased while the stress was decreased because of an EDZ. When an EDZ was considered in the model, the tunnel inflow was increased about 20% compared to the case without an EDZ.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.468-479
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• 2019

It is essential to comprehend coupled hydro-mechanical behavior to utilize subsurface for the recent demand for underground space usage. In this study, we developed a new simulator for numerical simulation as a tool for researching to consider the various domestic field and subsurface conditions. To develop the new module, we combined OpenGeoSys, one of the scientific software package that handles fluid mechanics (H), thermodynamics (T), and rock and soil mechanics (M) in the subsurface with FLAC3D, one of the commercial software for geotechnical engineering problems reinforced. In this simulator development, we design OpenGeoSys as a master and FLAC3D as a slave via a file-based sequential coupling. We have chosen Terzaghi's consolidation problem related to single-phase fluid flow at a saturated condition as a benchmark model to verify the proposed module. The comparative results between the analytical solution and numerical analysis showed a good agreement.