• Title, Summary, Keyword: 인강도 지수

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The Point Load Index of the Daegu Shale and its Relation to the Uniaxial Compressive Strength (대구지역 셰일의 점재하지수 특성 및 일축압축강도와의 상관성)

  • Lee, Younghuy;Youn, Chanho
    • Journal of the Korean Geoenvironmental Society
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    • v.10 no.3
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    • pp.37-45
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    • 2009
  • The experimental study was carried out to evaluate the characteristics of the point load index and the uniaxial compressive strength of inherently anisotropic shale in the laboratory. In the testing program the effects of size and the shape on the point load index were investigated both in the axial and diametral direction. In general, the point load index of the shale was constant when the length/diameter (L/D) ratio of the specimen is greater than 1.0 in the diametral direction. The point load index in axial direction shows slight decrease as the L/D ratio is increased and the corner breakage was observed when L/D ratio is greater than unity. The minimum point load index was observed in the bedding angle of $\beta=15^{\circ}{\sim}30^{\circ}$ in the axial point load tests and of $\beta=30^{\circ}$ in the uniaxial compression tests. The relationship between the point load index and the uniaxial compressive strength was linear to ${\sigma}_c=25.0 I_{s(50)}$ for the specimen with the bedding plane angle, $\beta$ at the range of $0^{\circ}{\sim}90^{\circ}$. On the other hand, this relationship was appeared linear to ${\sigma}_c=14.4 I_{s(50)}$ when the bedding angle, $\beta$ is fixed to 90${^{\circ}}$ and this correlation is much different from ${\sigma}c=22 I_{s(50)}, which is generally applied to the rock specimen with no bedding plane in ISRM (1985). The anisotropic strength with different $\beta$ angle shows the shoulder type and this can be suitably modelled by the corrected Ramamurthy'(1993)s equation with the index value of 'n' equal to 3.0.

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양성전분을 이용한 신문용지의 품질개선 및 생산성 향상

  • Lee, Hak-Rae;Ryu, Hun;Ham, Chung-Hyeon;Choi, Cheol-Hui;Jo, Seok-Cheol
    • Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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    • pp.33-33
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    • 1999
  • 고지 사용율을 증가시킴으로써 원가 절감을 모색하고 있는 국내 신문용지 생산업체에서 는 보류도와 탈수성 저하에 따른 생산성 악화가 발생하고 있을 뿐 아니라 제품의 강도 및 인쇄적성 저하라는 문제를 극복하는 것이 매우 중요한 과제로 대두되고 있다. 또 신문용지 생산공정의 수질이 악화됨에 따라서 사용되는 화학첨가제의 효능이 크게 감소하는 문제를 지니고 있다. 적합한 양성전분과 이러한 문제를 종합적으로 해결하기 위한 방안으로 신문용지 생산에 이의 적용기술을 모색하였다. 전기전도도가 4000 $\mu\textrm{s}$/cm인 신문용지 지료를 이용하여 DS 0.03인 저치환 양성 전분의 보류도 증가효과를 평가한 결과 양성전분을 사용하지 않은 경우에 비하여 보류도 증가율이 6 6%로 낮게 나타났으나, DS 0.06인 전분은 보류도 증가율이 21%로 향상효과가 높게 나타났 다. 또 양성전분의 치환도가 증가할수록 인장지수, 내부결합강도, 표면강도 향상 효과도 증 가되는 결과를 얻을 수 있었다. 가교 처리를 실시한 치환도 0.08 및 0.1의 습식양성전분의 경우에는 미세분 보류도, 여수도, 탁도 등에 큰 효과를 나타내지 않았다. 경우 보류도가 각 확인하였으며,이 건식방법으로 제조된 치환도 0.08 빛 0.15인 양성 전분을 0.5% 첨가할 각 16%, 21% 증가되어 적은 첨가량에서도 보류향상 효과가 높다는 것을 러한 효과는 여수도 및 양이온 요구량 측정을 통하여 재확인되었다. 저치환 양성전분의 성능을 개선시키기 위한 방법으로서 비이온성 천연고분자를 활용하 는 방안을 검토한 결과 비이온성 천연고분자를 병용함에 따라 보류도 증가율이 탁월하게 개 선되었으며, 인장지수, 내부결합강도, 표면강도 등에서도 같은 효과를 얻을 수 있었다.

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A Change of Shear Bond Strength of Orthodontic Resin Adhesives under Water Immersion (침수후 시간에 따른 교정용 레진접착제의 전단결합강도 변화)

  • Lee, Je-Jun;Kim, Jong-Chul
    • The korean journal of orthodontics
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    • v.28 no.5
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    • pp.783-789
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    • 1998
  • The purpose of this study was to evaluate the changes of shear bond strengths and failure patterns in orthodontic resin adhesives according to the water immersion time. Metal brackets were bonded to the specimens involving the premolars with chemical-cured($Concise^{\circledR}$) and light-cured($Transbond^{\circledR}$) adhesives. The shear bond strength was measured on universal testing machine and the failure patterns were assessed with the adhesive remnant index(ARI) after storage in distilled water at $37^{\circ}C$ for 1 day, 1 week and 1, 3, and 6 months, respectively. The results were as follows. 1. The shear bond strengths at the 6 month in both Concise and Transbond were significantly higher than those at the 1 day, 1 week and 1 month(p<0.05). There were positive correlations between shear bond strength and water immersion time in both Concise and Transbond(P<0.01). 2. There were no significant differences in shear bond strength between Concise and Transbond. 3. The brackets were failed primarily at the bracket base-adhesive interface and there was no significant difference in the incidence of ARI scores according to the water immersion time.

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Effect of Rapid Mixing Intensity and Coagulant Dosages on Phosphorus Removal by Coagulation (응집을 이용한 인의 제거에 급속혼화강도 및 응집제 주입량이 미치는 영향)

  • Han, Hyun-Jin;Moon, Byung-Hyun
    • Clean Technology
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    • v.18 no.4
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    • pp.404-409
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    • 2012
  • In this study, the effects of mixing intensity and coagulant dosages on the characteristics of floc growth for phosphorus removal were investigated. The experiments were conducted under Al/P molar ratio of 1.0, 1.5 and 2.0; rapid mixing intensity with G value of 100, 300, and 500 $s^{-1}$. The characteristics of floc growth were measured by flocculation index (FSI) and the removal efficiencies of phosphorus by using different size filters. The removal efficiencies of soluble phosphorus increased as Al/P molar ratio and rapid mixing intensity increased. However, the highest removal efficiencies of T-P were observed at G value of 300 $s^{-1}$. When Al/P molar ratio was lower than 1.0, the value of FSI at G value of 500 $s^{-1}$ was the largest. However, when Al/P ratio was larger than 1.0, the value of FSI at G value 300 $s^{-1}$ was the largest. Effects of mixing intensity and Al/P molar ratio on coagulation for phosphorus removal of synthetic and real wastewater effluent were observed to be similar.

Cyclic Shear Characteristics of Nakdong River Sand Containing Fines with Varying Plasticity (낙동강 모래에 포함된 세립분의 소성지수에 따른 반복전단 특성)

  • Park, Sung-Sik;Kim, Young-Su;Kim, Sung-Ho
    • Journal of The Korean Society of Civil Engineers
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    • v.31 no.3C
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    • pp.93-102
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    • 2011
  • Most experimental studies on soil liquefaction are related to clean sands. However, soils in the field or reclaimed grounds commonly contain some amounts of silt and clay rather than clean sand only. Many researchers investigated the effect of fine contents on liquefaction resistance and mainly used non-plastic fines such as silts. In this study, 10% of plastic fines with various plasticity index (PI) such as 8, 18, 50, and 377 were mixed with wet Nakdong River sand and then loose, medium, and dense specimens were prepared by undercompaction method. A series of undrained cyclic triaxial tests were carried out by applying three different cyclic stress ratios. As a result, the liquefaction resistance tended to decrease as a PI of fines in the specimens with equal fine content increased. On the other hand, the difference between loose specimens with low and high plasticity fines was not clearly observed in terms of liquefaction resistance. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as a plasticity of fines increased.

Estimation of the Flash Flood Severity using Flash Flood Index (돌발홍수지수를 이용한 돌발홍수심도 산정)

  • Kim, Eung-Seok;Choi, Hyun-Il;Lee, Dong-Eui;Kang, Dong-Jin
    • Journal of Korean Society of Hazard Mitigation
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    • v.9 no.6
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    • pp.125-131
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    • 2009
  • The aim of this study is to quantify the severity of flash food for a study watershed in Korea by estimation of flash food index using flood runoff hydrograph following Bhaskar et. al (2000). As an extension of the previous research, we examine the relation between flash food index and rainfall intensity, rainfall duration, and total runoff, respectively. This study has estimated the flash food index through simulated flood hydrographs to investigate the relative severity of flash flood in an ungauged basin, Megok river basin for 31 flood events.

A Study on the Determination and Characteristics of Stress Intensity Factors and Stress Singularities for V-notched Cracks in Dissimilar Materials (이종재료간 V-노치균열의 응력특이성과 응력강도계수의 특성 및 결정에 관한 연구)

  • 조상봉;윤성관
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.10
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    • pp.1890-1899
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    • 1992
  • In bonded structures, there are V-notched cracks in dissimilar materials and the stress concentration of these V-notched cracks causes to occur interface cracks in dissimilar materials Therefore the strength evaluation of V-notched cracks in dissimliar materials seems to be important. The stress fields of a V-notched cracks is known as .sigma.$_{ij}$ .var. K $r_{p-1}$,where K is the stress intensity factor and p-1 is the stress singularity. When the distance, r, approaches to 0 at the stress fields of V-notched cracks, the stresses become infinites by two more stress singularities of p-1 and p-1 is no more -0.5. Stress singularities and stress intensity factors for V-notched cracks in dissimilar materials are treated and discussed. The Newton-Raphson method which is an efficient numerical method for solving a non-linear equation is used for solving stress sigularities. And stress intensity factors are solved by the collocation method using the Newton-Raphson and least squares method. The effects of stress intensity factors and stress singularities on stress fields of V-notched cracks in dissimilar materials are studied by using photoelasic isochromatic frings patterns obtained from computer graphics.s.

Effect of Steel-fiber Distribution on Flexural Strength and Toughness of Shotcrete-mimicked Concrete Specimen (숏크리트 모사 콘크리트 공시체에 혼합된 강섬유의 분산도가 휨강도 및 인성에 미치는 영향)

  • Park, Sung-Sik;Kim, Sang-Jung
    • Journal of the Korean Geotechnical Society
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    • v.29 no.6
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    • pp.53-62
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    • 2013
  • A 5-20 cm thick shocrete has been routinely constructed for NATM tunneling method to stabilize and confine the excavated rock of tunnel construction site. A $40kg/m^3$ of steel fibers are usually mixed into such shotcrete but these steel fibers may not be evenly distributed depending on shotcrete machines, mixing ratios and excavated rock conditions. In this study, square column shotcrete-mimicked concrete specimens of $15cm{\times}15cm{\times}55cm$ were prepared with 5 equal layers and 5 or 20% cement ratio. The specimens were prepared with different reinforced-patterns: non-reinforced, middle layer-reinforced, 1, 3, and 5 layers-reinforced, or all layers reinforced. The specimens were air-cured for 7 days and tested for flexural strength. The influence of steel-fiber distribution on flexural strength and toughness of shotcrete-mimicked concrete specimens was investigated. In the case of a specimen with cement ratio of 20%, a flexural strength increased as a number of fiber-reinforced layer increased. The flexural strength of one-layer reinforced specimen showed 20% less than that of evenly fiber-distributed specimen. On the other hand, a specimen with cement ratio of 5% decreased as the number of fiber-reinforced layers increased. A toughness index increased as the number of fiber-reinforced layers increased, regardless of cement ratios. The toughness index of evenly fiber-distributed specimen showed 2-3 times as large as that of one-layer reinforced specimen.

The Lead-Lag Relationship between KOSPI 200 Spot and Futures Markets : Error Coreection Model (현 선물간 선.후행성에 관한 연구: 오차수정모형)

  • Byun, Jong-Cook
    • The Korean Journal of Financial Management
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    • v.17 no.1
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    • pp.227-251
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    • 2000
  • 한국시장에서 KOSPI 200 현물과 KOSPI 200 주가지수 선물간의 선 후행성을 실증적으로 분석하기 위하여 1998년 8월부터 1999년 10월까지 KOSPI 200 지수와 유동성이 가장 높은 최근 월물 가격의 5분 간격 자료를 이용하였다. 현 선물 가격의 안정성(stationarity)을 검증한 이후 공적분(cointegration)을 통하여 유도된 오차수정모형(Error Correction Model) 인과관계 회귀식을 GMM(Generalized Method of Moments)으로 추정하여 현 선물간의 선 후행성을 분석하고, 그 원인을 빈번하지 않는 거래(infrequent trading) 문제, 공매의 제약 문제, 거래 활발성의 강도 차이 문제 등의 측면에서 분석하였다. 그 결과 한국시장에서 현 선물간에는 쌍방의 인과 관계가 존재하지만 현물이 선물을 선행하는 정도는 아주 미약하였다. 반면에 선물은 현물을 약 30분 정도 선행하였다. 본 연구의 검증기간과 이용된 자료 내에서 현물이 선물에 대하여 후행하는 주된 원인은 현물시장에 존재하는 공매의 제약과 선물에 비하여 상대적으로 저조한 거래 활발성 때문인 것으로 나타났다. 왜냐하면 현물시장에서 공매가 상대적으로 어려운 시장하락시기에 선물의 선행정도가 통계적으로 유의적이었고, 현물과 선물의 거래가 활발한 시기에는 상호간에 선 후행성이 없었지만 현물의 거래가 비 활발할 경우 선물의 선행이 유의적이었기 때문이다.

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The Change of Pillar Strength due to Joint Dip Angles, Total Trace Length and Width-to-Height ratio of a Pillar (절리면의 방향, 절리선 길이 및 광주 형상비가 광주 강도에 미치는 영향 분석)

  • Choi, Ji-won;Lee, Yong-Ki;Song, Jae-Joon
    • Tunnel and Underground Space
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    • v.30 no.3
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    • pp.226-241
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    • 2020
  • The stability of underground mine cavity is closely related with pillar strength. The vulnerability of pillars can be judged and reinforced if the pillar strength is known. The pillar strength is affected by characteristics of discontinuities and shape of a pillar. The change of pillar strength due to a discontinuity passing through the center of a pillar, width-to-height ratio of a pillar and small joints existing within a pillar was analyzed using PFC 3D. The result showed that the pillar strength is influenced by dip angle of a discontinuity and it increases as width-to-height ratio of a pillar increases. The pillar strength decreases as the number of contained joints increases. The relationship between total trace length observable from the pillar surface and the pillar strength was regressed with exponential function. The correlation coefficient of the regression was high enough so that pillar strength can be predicted using total trace length if a joint set exists in a pillar. Lastly, the method to estimate the strength of a pillar that includes two joint sets was proposed if the joint dip angles are 60°, 30°. The method also need total trace lengths of two joint sets.