• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.28-28
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• 2015

현재 인쇄전자 소자 생산을 위해 사용되고 있는 대부분의 그라비아 롤러는 미세 패턴의 보호와 인쇄 중 마찰에 대한 내구성을 향상시키기 위해 경질 크롬 도금 막이 사용되고 있다. 그러나 경질 크롬 도금 막의 경우 구현할 수 있는 경도(~1000 HV)와 이형성, 내마찰(마찰계수: ~ 0.6) 특성 등에 한계가 있다. 이러한 경질 크롬 도금이 적용된 그라비아 롤은 그 수명과 내구성, 구현할 수 있는 인쇄 품질 및 신뢰성 그리고 인쇄처리 속도 등에 있어 여러 문제가 있다. DLC(Diamond Like amorphous Carbon)는 낮은 마찰계수 값인 0.2 이하와 뛰어난 내마모성, 상대재료에 대한 이형성 등을 겸비한 표면강화 기술로 경질 크롬 도금막 대비 우수한 표면 경도(>1,800 HV) 특성을 갖으며, 합성된 DLC 코팅 막의 경우 정밀 인쇄 제판이 요구하는 표면거칠기를 구현할 가능성이 높다는 장점이 있다. 특히 실리콘이 첨가 된 Si-DLC의 경우 표면의 마찰계수를 0.1 이하까지 낮출 수 있는데 닥터블레이드 및 잉크, 인쇄 기재와의 마찰 훼손을 최소화시켜 그라비아 인쇄 롤의 수명을 향상시킬 수 있다. 또한 PECVD 공정을 이용하여 합성한 Si-DLC는 표면거칠기를 10nm 이하의 경면으로 구현할 수 있으며, 높은 접촉각에 의한 우수한 이형성을 통해 미세 패턴 내부에 전자잉크/페이스트가 잔류되는 현상을 억제할 수 있다. 이는 기존 경질 크롬 도금이 적용된 그라비아 롤에서 발생하는 패턴 내 잉크 잔류-고형화와 그에 의한 사용수명 단축현상을 현저히 개선시킬 수 있다.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.85-101
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• 2020

The estimation of strength parameters is very important for the stability analysis of rock slopes. Various methods for the determination of strength parameters were suggested by various researchers. The number of methods used for the estimation of strength parameters in the stability analysis of rock slopes were investigated based on literature reviews. The frequency of the method determining strength parameters were investigated with respect to failure types. The cohesion and friction angles of the rock and discontinuities are presented with RMR values. The cohesion shows wider range of values relative to those of friction angles according to current studies. Even though RMR does not show any correlation with cohesion values, RMR and the friction angle of the rock clearly shows a positive relationship. Proper methods should be utilized for the determination of strength parameters with consideration for failure types and be proved through literature reviews. The credibility of determining strength parameters is expected to improve if strength parameters data are accumulated from the back analysis performed for failed local rock slopes.

• Journal of the Korean GEO-environmental Society
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• v.8 no.1
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• pp.49-55
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• 2007

In order to utilize treads of waste tire as reinforcement material it is necessary to know the interface friction angle between tread surfaces and soil and tensile strength of connection joint of tire treads. In this research large direct shear tests were performed to get the interface friction angle between the inner and outer surfaces of treads and soil for different degree of compaction. From the large direct shear tests, the ratio of interface friction angle to the shear friction angle of sand, ${\delta}/{\phi}$, were 1.06 in outside surface of tire tread and 0.93 in inside surface of tire tread. For weathered granite soil the ratio of interface friction angle was 0.98 and 0.92 for outside and inside of tread, respectively. Also tensile tests were performed using universal testing machine for the connection joint of treads and Tirecell units using bolts. The tensile strength of connection joint increased with the number of bolts and with the sizes of washers. Connection by polypropylene ropes showed lower strength than those of bolts.

• Journal of the Korean Geotechnical Society
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• v.39 no.7
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• pp.17-30
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• 2023

This study investigates the impact of water immersion and high temperature on the shear strength of cemented sand through direct shear tests. Standard Jumunjin sand was used and cemented with binders, such as ultra-rapid hardening cement and an epoxy aqueous solution. The binder was mixed at concentrations of 4%, 8%, or 12%. Subsequently, cylindrical cemented specimens with a diameter of 64 mm and height of 25 mm were produced using compaction. The curing period was three days, and the specimens were cured under dry air, immersion, and heating conditions. The heating condition involved subjecting the immersed specimens to a microwave oven three times for three minutes to achieve an internal temperature of approximately 90℃. Regardless of the binder type, the cohesion of the cemented sand increased with higher binder content, whereas the internal friction angle exhibited a slight increase or decrease. Compared with ultra-rapid hardening cemented sand, epoxy-cemented sand displayed an average cohesion that was five times higher and an internal friction angle that was 10° higher. Overall, irrespective of binder type, the shear strength decreased during water immersion and increased during heating. Notably, the epoxy-cemented sand exhibited a three-fold increase in cohesion and a more than 20° increase in the internal friction angle during heating.

• Journal of the Korean Geosynthetics Society
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• v.15 no.3
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• pp.67-76
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• 2016

The railway bridge abutment subjected to the lateral earth pressure is a sensitive structure that is affected by backfill materials, installation methods, compaction, and drainage system and so on. The several design loads for the bridge abutment design consist of traffic loading on bridges and vertical & lateral force due to surcharge load at backfill. Especially, the lateral earth pressure of design load components is important and considered in the design of geotechnical engineering structure such as bridge abutment wall. The determination of cross section for abutment is finally determined with calculating external stability and member force of abutment wall structures. In this study, the abutment wall height is 12m and the optimal cross section of abutment wall has been determined that satisfies an external stability for abutment structure through friction angles of 35, 40, and 45 degrees of backfill materials. The external stability and member force of abutment wall with friction angle of backfill materials and were calculated and construction cost of each abutment wall structures was compared. It found that the construction cost was reduced from 2.2 to 8.4% with friction angle of backfill materials.

• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.1
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• pp.38-51
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• 1984

Mononobe-Okabe에 의해서 옹벽에 대한 동적 토압계산법이 개발된 이래 본론두중 옹벽의 과동에 의한 변위에 대해서는 많은 연구가 이루어졌으나 Mononobe-Okabe식이 원래 옹벽 자체의 관성을 고려치 아니하였고 또 동적 하중의 작용점을 제시하지 않으므로서 전도모멘트를 계산할 수 없게 하므로서 옹벽의 전도에 의한 변위에 대해서는 연구가 되지 아니하였다. 본 연구의 목적은 해석적 방법과 모형실험을 통해서 지진 및 폭파 등의 동적 하중에 의한 옹벽의 전도에 의한 변위를 고찰하고자 하는 바 그 결과를 요약하면 다음과 같다. 1. 활동에 대한 항복가속도가 있는 것과 마찬가지로 전도에 대한 항복가속도가 있다. 이 항복가속도는 옹벽의 안전율이 증가함에 따라 증가한다. 2. 이론치와 실험치는 경향으로 보아 일치한다. 실험치가 이론치보다 작은 것은 모형실험에서 옹벽측면과 컨테이너 사이의 마찰에 기인한 것으로 보아지며 마찰을 줄임으로써 이론치에 더 접근시킬 수 있을 것이다. 3. 옹벽의 회전각도의 크기는 지반가속도가 클수록, 옹벽저면이 작을수록 그리고 흙의 내부마찰각이 작을수록 크게 증가한다. 4. 실용적인 규격의 옹벽의 변위는 활동에 의한 것보다 전도에 의한 것이 훨씬 크며 전체 변위의 대부분을 차지한다. 5. 옹벽 상단의 횡적 변위는 옹벽 설계를 결정짓는 중요한 요소가 될 수 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.425-433
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• 2019

In this study, a simple method of calculating the passive earth pressure coefficient, which is based on the limit equilibrium method, was proposed and the calculated earth pressure coefficients were compared with those of several researchers. The angle of the linear failure surface, which is combined with the logarithmic spiral arc, to the failure surfaces of the passive zone was derived and the whole passive thrust acting on the Rankine passive zone was considered in the proposed method instead of considering the horizontal component of passive thrust. The variations of the passive earth pressure coefficients of the proposed method showed the same tendency as that of the Coulomb's passive earth pressure coefficients with an inclined angle of backfill and internal friction angle. The magnitude of passive earth pressure coefficients of the proposed method were smaller than those of the Coulomb in almost all cases. A comparison of the passive earth pressure coefficients with the wall friction angle revealed the passive earth pressure coefficients of the proposed method to be smaller than those of the Coulomb and the differences between the two values increased with increasing internal friction angle and wall friction angle. A comparison of the passive earth pressure coefficients of the proposed method with those of the existing researchers for the considered internal friction angles of $25^{\circ}$, $30^{\circ}$, $35^{\circ}$, and $40^{\circ}$ and three wall friction angles revealed the maximum percentage differences for the Kerisel and Absi method, Soubra method, Lancellotta method, $Ant\tilde{a}o$ et al. method, Kame method, and Reddy et al. method to be 4.8%, 3.8%, 31.1%, 4.0%, 20.6%, and 12.8% respectively. The passive earth pressure coefficient and existing pressures were similar in all cases.

• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.81-91
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• 2013

This paper investigates the shear properties of bottom ash-crumb rubber mixture reinforced with waste fishing net. Mixtures used in this experiment were prepared at 2 different percentages of crumb rubber (2 mm~10 mm) content (i.e., 0%, 50% by weight of the dry bottom ash). In this study several series of triaxial tests were carried out on the six different specimens : unreinforced bottom ash, reinforced bottom ash with 1 or 2 layers, unreinforced mixture, reinforced mixture with 1 or 2 layers. The experimental results indicated that the shear properties of bottom ash-crumb rubber mixture were strongly influenced by reinforcing layer of waste fishing net and crumb rubber addition. It is shown that the internal friction angle of bottom ash-crumb rubber mixture decrease with addition of crumb rubber due to the compression properties of crumb rubber. However, the internal friction angle of the mixture increased with an increase in reinforcing layer due to interlocking effect and friction between mixture and waste fishing net.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.219-227
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• 2013

Although Mohr-Coulomb failure criterion has limitations in that it is a linear criterion and the effect of the intermediate principal stress on failure is ignored, this criterion has been widely accepted in rock mechanics design. In order to overcome these shortcomings, the Hoek-Brown failure criterion was introduced and recently a number of 3-D failure criteria incorporating the effect of the intermediate principal stress on failure have been proposed. However, in many rock mechanics designs, the possible failure of rock mass is still evaluated based on Mohr-Coulomb criterion and most of practitioners are accustomed to understanding the strength of rock mass in terms of the internal friction angle and cohesion. Therefore, if the equivalent Mohr-Coulomb strength parameters of the advanced failure criteria are calculated, it is possible to take advantage of the advanced failure criteria in the framework of the Mohr-Coulomb criterion. In this study, a method expressing the tangential Mohr-Coulomb strength parameters in terms of the stress invariant is proposed and it is applied to the generalized Hoek-Brown criterion and the HB-WW criterion. In addition, a new approach describing the geometric meaning of the ${\sigma}_2$-dependency of failure criteria in 3-D principal stress space is proposed. Implementation examples of the proposed method show that the influence of the intermediate principal stress on the tangential friction angle and cohesion of the HB-WW criterion is considerable, which is not the case for the 2-D failure criterion.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.153-166
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• 1991

In an attempt to investigate the effect of intermedate principal stresses which are related to the stress-strain behavior of standard sands, a series of three-Principal stress control tests were conducted for individual stress paths. The results have shown that shear strengths of sands vary with the stress paths. The variations in internal friction angle are accorded with the Habibs stress parameter, b which represents Stress paths, showing on abropt increase at the values between 0.0 and 0.268, a moderate level between 0.268 and 0.682, and a slight decrease between 0.682 and 1.0 However, the friction angles under a triaxial extention state, were found relatively larger than under a triaxial compression state. In general, such veriations were found to have the same tendency without any relevant relation with the density of specimens and confining pressures. Therefore, it is concluded, that the shear strength of sands are positively influeced by the intermediate principal stresses present in the media. And the influnce of intermediate principal stresses on shear strengths of sands found from the present study are well compared with the previous studies by Lade-Duncan and Matsuoka-Nakai revealing a similar tendency within the failure criteria proposed by them.