• Journal of the Korean Geotechnical Society
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• v.35 no.9
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• pp.5-13
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• 2019

The soil-water characteristic curve (SWCC) plays an important role in determining the soil suction parameters required to predict the seepage or shear behaviors of unsaturated soils. In addition, path dependency of the SWCC affects the mechanical and hydrologic behaviors. In general, there is a disadvantage that it takes a long time to measure both the drying and wetting paths of the SWCC by a stepwise pressurization method. Thus, the continuous pressurization method as an improved testing method for the SWCC was suggested, and the testing time for two paths of the SWCC was significantly shorter than the conventional methods. For the applicability evaluation of this method, the results of the SWCC obtained by the stepwise pressurization method and the evaporation method in this study were compared to the result obtained from this method. As a result, it was found that the difference among three methods was negligible, and the testing time of the continuous pressurization method was greatly decreased. Therefore, it can be said that it is possible to quickly and accurately measure the SWCC under various conditions by the continuous pressurization method.

• Composites Research
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• v.33 no.6
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• pp.371-376
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• 2020

The adhesive strength can be improved through surface treatment. The most common method is to improve physical bonding by varying the surface conditions. This study presents the effect of laser surface treatment on the adhesive strength of CFRP. The surface roughness was patterned using a 1064 nm laser. The effects of the number of laser shots and the direction and length of the pattern on the adhesion of the CFRP/CFRP single joint were investigated through tensile tests. Tests according to ASTM D5868 were performed, and the bonding mechanism was determined by analyzing the damaged surface after a fracture. The optimized number of the laser shots and the optimized depth of the roughness should be required to increase the bonding strength on the CFRP surface. When considering the shear stress in the tensile direction, the roughness pattern in the direction of 45° that increases the length of the fracture path in the adhesive layer resulted in an increase of the adhesive strength. The surface treatment of the bonding surface using a laser is a suitable method to acquire a mechanical bonding mechanism and improve the bonding strength of the CFRP bonding joint. The study on the optimized laser process parameters is required for utilizing the benefits of laser surface processing.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.3
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• pp.141-148
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• 2021

In this paper, we propose an algorithm of welding bead detection and evaluation using geodesic active contour algorithm and high pass filter with image processing technique. The algorithm uses histogram equalization and high pass filter as gaussian filter to improve contrast. The image processing techniques smoothens the welding beads reduce the noise on an image. Then, the algorithm detects the welding bead area by applying the geodesic active contour algorithm and morphological ooperation. It also applies the balloon force that either inflates in, or deflates out the evolving contour for a better segmentation. After that, we propose a method for determining the quality of welding bead using effective length and width of the detected bead. In the experiments, our algorithm achieved the highest recall, precision, F-measure and IOU as 0.9894, 0.9668, 0.9780, and 0.8957 respectively. We compared the proposed algorithm with the conventional algorithms to evaluate the performance of the proposed algorithm. The proposed algorithm achieved better performance compared to the conventional ones with a maximum computational time of 0.6 seconds for segmenting and evaluating one welding bead.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.561-577
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• 2021

The compacted bentonite buffer in a geological repository for high-level radioactive waste disposal is saturated due to groundwater inflow. Saturation of the bentonite buffer results in bentonite swelling and bentonite penetration into the rock discontinuities present around the disposal hole. The penetrated bentonite is exposed to groundwater flow and can be eroded out of the repository, resulting in bentonite mass loss which can affect the physical integrity of the engineered barrier system. Hence, the evaluation of buffer-rock interactions and coupled behavior due to groundwater inflow and bentonite penetration is necessary to ensure long-term disposal safety. In this study, the effects of the bentonite penetration and swelling on the physical properties of jointed rock mass were evaluated using the quasi-static resonant column test. Jointed rock specimens with bentonite penetration were manufactured using Gyeongju bentonite and hollow cylindrical granite rock discs obtained from the KAERI underground research tunnel. The effects of vertical stress and saturation were assessed using the P-wave and S-wave velocities for intact rock, jointed rock and jointed rock with bentonite penetration specimens. The joint normal and joint shear stiffnesses of each joint condition were inferred from the wave velocity results assuming an equivalent continuum. The joint normal and joint shear stiffnesses obtained from this study can be used as input factors for future numerical analysis on the performance evaluation of geological waste disposal considering rock discontinuities.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.64-72
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• 2022

In this study, in order to confirm the seismic performance of reinforced concrete frames retrofitted with Wall Friction Damper(WFD), the test was conducted by setting two-story Reinforced concrete frames (reference specimen, OMF-N and specimen retrofitted with internal H-shaped steel frame and WFD, OMF-ALL(H)) as main variables. The WFD Seismic Retrofit Method is a mixture of strength improvement and energy dissipation methods. To prevent the pre-destruction of existing structure by friction force before sufficient energy dissipation of WFD, the internal H-shaped steel frame and chemical anchor that penetrates the side of the beam were used to install WFD. According to the test results, the OMF-N specimen showed an brittle failure pattern caused by the shear force of the R/C column after the maximum strength was expressed. The OMF-ALL(H) specimen showed that the reduction of pinching effect and the failure of the RC column occurred. Also, the maximum strength, cumulative energy dissipation and ductility of OMF-ALL(H) increased 3.01 times, 7.2 times and 1.72 times for OMF-N. As a results, test results revealed that the WFD Seismic Retrofit Method installed on Reinforced concrete structure improves the seismic performance and the strengthening effect is valid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.73-81
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• 2022

Recently, as the service life of structures increased, the load-carrying capacity of deteriorated reinforced concrete, where corrosion of reinforcing bars occurs due to various causes, is frequently decreased. In order to address this problem, many studies on the bond characteristic of FRP (Fiber Reinforced Polymer) bars with corrosion resistance, light weight and high tensile strength have been conducted, however there are not many studies on the bond characteristic of grid-typed CFRP embedded in concrete. Therefore, in order to evaluate the bond characteristics of grid-typed CFRP and its usability as a substitute for steel rebar, a pull-out test is performed using the longitudinal bond length and transverse grid length of the grid-typed CFRP as variables. Through the pull-out test, the bond load-slip curve of the grid-typed CFRP is derived, and the bond behavior is analyzed. The total bond load equation is proposed as the sum of the bond force of the longitudinal bond length and the shear force of the grid in the transverse direction. Also, expressing the area of the bond load-slip curve as total work, the change in dissipated energy with respect to the slip is analyzed to examine the effect of the tranverse grid on the bond force.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.78-85
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• 2023

This study evaluates the performance of reinforced concrete columns using hybrid fiber sheets for structural behavior. The purpose of this method is to improve the load-bearing capacity of the reinforced structure by impregnating a hybrid fiber sheet, which is woven by arranging aramid and glass fibers uniaxially and attached to an aged concrete structure requiring reinforcement with epoxy. In particular, not only the weight reduction of the material obtained by using a fiber lighter than the steel material, but also the low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element. The low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element, resulting in weight reduction compared to steel. The study conducted structural tests on four specimens, with the hybrid reinforcement method and failure mode as main variables. Specimen size and loading conditions were chosen to be comparable with previous studies. The structural performance of the specimen was evaluated using energy dissipation capacity and ductility. Analysis shows that excellent results can be obtained with the hybrid fiber sheet reinforcement.

• Journal of the Korean Geosynthetics Society
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• v.22 no.3
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• pp.11-25
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• 2023

In this study, the design and numerical analysis method of the inclined self-supported wall using cement treated soil were studied. In the case of the inclined self-supported wall, the active earth pressure decreased due to the decrease in the coefficient, Ka according to the slope (angle) and the weight decreasing effect, thereby increasing the overall stability. The wall with the slope caused a change in failure mode from overturning to sliding on the excavation side, and the optimal slope was evaluated to be about 10°. Compared to the strength reduction method, the overall stability in numerical analysis results in conservative results in limit equilibrium analysis, so it was found that this method should be attended when designing. As a result of the parameteric study, the stability on bearing capacity and compression failure did not significantly increase above the slope of 10° when the surcharge was small (about 20kPa or less). In the case of cohesion of the backfill, The results similar to numerical analysis were found to consider cohesion. It was evaluated that stability on sliding, oveturning, shear, and tension failure increases in proportion to the thickness of the wall, but there is no significant change in the stability on the bearing capacity and compressive failure regardless of the thickness of the wall above a certain angle (about 10°).

• Korean Journal of Mineralogy and Petrology
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• v.36 no.2
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• pp.95-106
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• 2023

Quartz (SiO₂) is among the major rock-forming minerals in the earth's crust. The atomistic structures of SiO₂ may evolve during diverse frictional processes. The reduction of friction of quartz-rock accompanied by its amorphization, hydration, and formation of silica gel provides mineralogical insights into earthquakes and related phenomena. Ball milling, together with rotary shear experiments have been useful to infer the atomic origins of such processes. In this study, optimal experimental conditions for ball milling for amorphization of SiO₂ were determined by taking into account various process variables. The crystallinity of SiO₂ gradually decreased and became amorphous as the ball milling time increased at a high milling speed. The degree of wear of the milling media and its effect on the amorphization of SiO₂ were analyzed using distinct milling materials (zirconia, stainless steel). The amount of ball wear increased with increasing milling time. Furthermore, the worn stainless steel particles from balls tend to interact with amorphized SiO₂ to form Si-O-Cr. These results aid in understanding the process of atomistic structural changes caused by ball milling of divserse materials with relatively high hardness, such as SiO₂, and understanding various geological friction processes.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.25-25
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• 2021

점착성 유사는 비점착성 유사에 비해 1차입자의 크기가 작아 1차입자간의 점착력이 중요한 역할을 하는 유사를 말한다. 점착성 유사는 비점착성 유사에 비해 크기가 작아 입자의 전자기적 점착력의 영향을 무시할 수 없으므로 점착력으로 인해 입자들은 서로 응집하는 동시에 입자들 간의 충돌에 의하여 파괴되는 과정을 거친다. 이러한 응집과 파괴가 지속되는 일련의 과정을 응집현상이라 한다. 점착성 유사는 응집과정을 통해 일차입자보다 크기가 크며 수십 개에서 수천 개의 일차입자와 물의 덩어리인 플럭을 형성하게 된다. 흐름 내 존재하는 플럭의 응집현상에 가장 지배적인 영향을 미치는 인자로 난류 거동이 알려진 바 있다. 본 연구에서는 난류 거동에 따른 점착성 플럭의 입도분포 변화를 살펴보고자 하였으며, 점착성 유사 입도분포 모형을 개발하였다. 수치모형의 개발은 확률과정(또는 추계과정)의 개념을 바탕으로 한다. 점착성 유사의 응집현상을 구성하는 응집과정은 다양한 연구를 통해 메커니즘들이 규명된 것과 달리 파괴과정은 난류로 인해 발생하며 무작위한 것으로 여겨진다. 무작위한 플럭의 파괴과정을 확률과정으로 가정하고 매개변수 중 하나를 대수정규분포를 따르는 난수로 고려하였다. 개발된 모형의 검증은 연안지역에서 점착성 플럭의 거동을 측정한 연구결과와의 비교를 통해 수행하였으며, 흐름 유속의 연직분포와 유사 농도의 연직분포, 응집현상 이후 플럭의 평형크기와 입도분포가 모두 합리적으로 계산되는 것이 확인되었다. 더불어 모의 결과에서는 대수정규분포를 따르는 동일한 난수를 적용하였음에도 불구하고 하상으로부터 거리가 가까워짐에 따라 플럭입도분포가 단봉분포(Unimodal Distribution)와 이봉분포(Bimodal Distribution)가 모두 계산되는 것으로 나타났다. 이는 모형의 개발과정에서 플럭의 가능 최대 크기를 콜모고로브 길이규모로 제한한 것과 관련이 있다. 난류 흐름 내 존재하는 플럭의 크기가 응집현상을 통해 난류의 콜모고로브 길이규모까지 성장하는 경우, 난류의 전단응력이 급격하게 증가하여 파괴과정이 활발해지고 응집과정이 저하된다는 것은 널리 알려진 사실이다. 이러한 사실을 바탕으로 플럭의 가능최대 크기를 콜모고로브 길이규모로 제한하였으며, 하상으로부터의 거리에 따라 콜모고로브 길이규모의 변화로 인해 콜모고로브 길이규모 부근에서 하나의 최빈값이 추가로 나타나는 것으로 이해된다. 수치모의 결과로부터 얻어진 콜모고로브 길이규모와 입도분포 형태의 상관관계를 보다 정확하게 이해하기 위해 실측 자료들을 검토해 본 결과, 균질한 재료를 이용한 실험실 실험결과에서 플럭 이봉분포의 최빈값이 콜모고로브 길이규모와 일치하는 것이 확인되었다. 연안지역에서 측정을 수행한 자료들에서도 이봉분포 또는 다봉분포와 콜모고로브 길이 규모와의 상관성을 찾아볼 수 있었다.