• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.137-144
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• 2005

A direct shear test is classified roughly by one side simple shear test of confining horizontal displacement type and torsional shear test of non-confining one. Direct shear test that has been widely used so far has some problems with test apparatus, testing and the analysis, and in particular that its strength value is everestimated in sandy soils. Also, progressive failure of shearing process happens from shear apparatus restriction and because the shear strain and shear stress are erratic in specimen, we can not define the shear strain value. In the meantime, a simple shear test having advantage of direct shear test is an ideal test method that can get stress-strain relation on shear because it can deliver constant shearing deformation to specimen. However, simple shear test cannot be used practically, because its structure makes tester manufacturing difficult. This paper described a on outline of test apparatus, improvement of test method, and constant pressure test results based on the obtained from improved direct shear apparatus and the standardization of JGS soil testing method.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.590-596
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• 2019

Purpose: An experimental study was conducted on the sand samples for the size effect of the test specimens, one of the problems of the direct shear test. Method: Jumunjin standard sand, a representative sand of Korea, was used as sand sample. The large direct shear test was performed to analyze the shear strength at 50%, 60%, 70%, and 80% relative density, and then the comparative results were compared with the test results of the small direct shear test. Result: It was analyzed that the internal friction angle of the small shear tester tended to be relatively large in the dense region. It was analyzed that the results of the large shear tester tend to be relatively large in the region of medium relative density. Conclusion: The size effect on the samples in the direct shear test on sandy soil was analyzed to be relatively small.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.46-54
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• 2014

Direct shear tests have been initiated to understand the characteristics of joints which crucially affect the stability of rock mass. In this research, numerical approach in direct shear tests has been initiated using 3DEC on the basis of 3D distinct element method. Normal loads were altered in four different levels on artificial joint tests depending on the sawtooth angle and strengths on constant normal stress conditions, measuring the peak shear strength according to the direct shear tests under laboratory condition. Also results obtained from mechanical properties through laboratory test were used to perform numerical modeling, and shear strength obtained from the modeling was used to compare with laboratory direct shear test. As a result numerical analysis from distinct element method can simulate well on the shear behavior of rockmass.

• Journal of the Korean Geotechnical Society
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• v.27 no.2
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• pp.43-52
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• 2011

The characteristics of shear zone in granular soils largely affect the stability of geo-structures. The goal of this study is to evaluate shear zone in a direct shear test using shear wave, electrical resistivity, and cone tip resistance. Bender elements and electrical resistivity probe are embedded into the wall of a direct shear box made of transparent acrylic material to estimate the shear wave velocities and the electrical resistivity at shear and non-shear zones. At the point of peak and residual strength, micro cone penetration test which can be available to measure tip resistance has been performed. Experimental results show that the shear wave velocities at upper shear zone increase during shearing while the values remain constant at bottom and lower shear zone. Also, resistivities at lower shear zone depend on relative density while resistivities at bottom remain constant. The results of cone penetration test demonstrate the correlation of the cone tip resistance and small strain shear modulus at shear zone. This study suggests that the application of the modified direct shear box including shear wave, electrical resistivity and the micro cone tip resistance may become effective tools for analyzing the characteristics of a shear zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2C
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• pp.73-80
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• 2006

The shear behavior of four different interfaces consisting of four types of geosynthetics was investigated, and both static and dynamic test for the geosynthetic interfaces were conducted. The monotonic shear experiments were performed by using an inclined board apparatus and large direct shear device. The interface shear strength obtained from the inclined board test was compared with calculated values from large direct shear tests. The comparison results indicated that direct shear tests show high possibility to over-predict the shear strength in the low normal stress range where direct shear tests are not performed. Curved failure envelopes were also obtained for interface cases where two static shear tests were conducted. By comparing the friction angles measured from three tests, i.e. direct shear, inclined board, and shaking table test, it was found that the friction angle might be different depending on the test method and normal stresses applied in the research. Therefore, it was concluded that the testing method should be determined carefully by considering the type of loads and the normal stress expected in the field with using the geosynthetic materials installed in the site.

• Journal of the Korean GEO-environmental Society
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• v.18 no.3
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• pp.5-14
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• 2017

Experimental study on strength characteristics of frozen soils is necessary for the safety evaluation of design and construction in cold region. The objective of this study is to evaluate the direct shear strength of frozen soils obtained from traditional system (Type-1), system with roller on the upper shear box (Type-2), and system with fixed upper shear box separated from bottom shear box (Type-3). Specimens mixed with sand, silt, and water are frozen to $-5^{\circ}C$, and then direct shear tests are conducted under the normal stress of 5, 10, 25, and 50 kPa. Experimental results show that the upper shear box of Type-1 touches the bottom shear box due to the rotation of the upper shear box. The shear strength obtained from Type-2 is overestimated because the preventing rotation force is added to shear force. Type-3 may acquire the only strength of the specimen, and shear strain at peak shear strength is similar to that at the beginning of vertical displacement occurrence. In addition, internal friction angle and cohesion at both peak and residual stresses in Type-3 are smaller than those of Type-2. This study shows that high strength specimens including frozen soils can be effectively evaluated using improved shear box system such as Type-3.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.551-558
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• 2020

This note presents the calculation of nominal area for rock core specimen under direct shear testing condition. The initial nominal area was assumed as ellipsoid, and the equations for calculating the nominal area are derived. The normalized shear displacement and normalized nominal area have an identical relationship regardless of the ellipsoid shape. New testing constants and the generalized method were suggested to calculate the decrease of the nominal area. The method was applied to calculate the direct shear testing data and the changes of result were discussed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.393-401
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• 2021

In this paper, we proposed a numerical model based on moment-curvature, to evaluate the resistance of reinforced concrete (RC) members subjected to blast loading. To consider the direct shear failure mode, we introduced a dimensionless spring element based on the empirical direct shear stress-slip relation. Based on the dynamic increase factor equations for materials, new dynamic increase factor equations were constructed in terms of the curvature rate for the section which could be directly applied to the moment-curvature relation. Additionally, equivalent bending stiffness was introduced in the plastic hinge region to consider the effect of bond-slip. To verify the validity of the proposed model, a comparative study was conducted against the experimental results, and the superiority of this numerical model was confirmed through comparison with the analytical results of the single-degree of freedom model. Pressure-impulse (P-I) diagrams were produced to evaluate the resistance of members against bending failure and direct shear failure, and additional parametric studies were conducted.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.70-70
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• 2016

하천시설물 설계, 시공 및 관리에 있어서 바닥전단응력은 매우 중요하다. 예를 들어, 호안 등 시설물의 허용 소류력을 계산하거나, 하천의 유사량을 예측하는 데 있어서 바닥전단응력이 기준으로 쓰인다. 정상 등류의 경우, 수로 내 수체에 작용하는 중력과 수로 바닥 및 측면에 작용하는 마찰력의 평형을 고려함으로써 바닥전단응력을 산정할 수 있다. 본 연구에서는 식생을 제외한 아크릴수로에서의 전단판의 움직임을 이용한 바닥전단응력 측정장치를 설계, 교정 및 검증을 실시하였다. 이 전단판은 수체와 바닥면에서 발생하는 마찰력에 의해 변위가 발생하고 이 변위를 바닥전단 응력으로 산정하였다. 직접 측정한 바닥전단응력은 기존에 연구된 두 가지 방법과 비교하여 검증하였다. 비교 검증을 위한 실험은 폭 0.3 m, 길이 10 m인 고속수로에서 Froude수 1이상, Reynolds수 20000이상의 사류이면서 난류인 상태로 실험을 진행하였으며 유속은 PIV을 이용하여 측정하였다. 비교 검증을 위한 첫 번째방법은 Reach-avrage공식을 기초로 manning의 평균 유속 공식을 이용한 바닥전단응력을 산정하는 방법으로 일반적으로 간단한 경험식을 이용하여 바닥 전단응력을 산정하는 방법이다, 두 번째는 Reynolds stress를 산정하는 방법으로 PIV를 통해 흐름방향의 연직프로파일의 유속을 측정 한 후 레이놀즈 분해법에 의해 산정된 난류 강도를 측정하여 Reynolds stress를 산정한 후 Shear stress를 산정하는 방법을 사용하였다. 마지막으로 본 연구에서 가로 0.14 m, 세로 0.14 m의 전단판으로 구성된 바닥전단응력 측정장치를 개발하여 실험을 진행하면서 앞에서 언급한 두가지 방법을 측정하는 동시에 장치를 이용하여 바닥전단응력을 직접측정하여 총 3가지 바닥전단응력을 비교하였다.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.185-196
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• 1998

이 논문은 직사각형 단면을 갖는 철근콘크리트 보에서 휨전단균열(Flexural-Shear Crack)이 원인을 규명하기 위해 모두 16개의 보를 실험한 결과를 기술한 것이다. 실험에 이용된 콘크리트보는 전단균열에 영향을 준다고 생각되는 몇 가지 요소를 인위적으로 소거 도는 고립되도록 특수하게 제작된 것이다. 이러한 특수보의 실험결과를 같은 재원을 갖는 보통의 정상보의 결과와 직접 비교하여서 그 차이를 분석함으로써 휨전단 균열의 발생원인을 규명하였다. 그 결과, 일반적인 콘크리트보에서의 휨전단균열 발생은 철근과 콘크리트의 경계면의 부착현상과 매우 밀접한 관련이 있는 것으로 나타났다. 또한 발생된 휨전단균열의 안정성은 주철근을 따라 발생되는 수평균열의 크기에 직접적인 영향을 받고 있는 것으로 나타났다. 본 연구에서 나타난 몇 가지 사실은 현재 사용중인 전단설계규준의 근본을 이루는 전단 위험단면개념과는 상반되는 것도 있었다. 실험에서 알아낸 사실을 근거로 전단파괴기구에 대한 새로운 가설을 제안하였다. 이 새 가설은 지금까지 잘 설명되지 않은 휨전단균열의 발생과 진행에 대한 원인 및 과정을 상당히 잘 설명해주고 있다고 생각된다.