• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.29-37
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• 2017

As the behavior of the debris flow due to the torrential rains in mountain is affected by shear strength and rheological properties of the fine fraction in the ground, the evaluation of both properties is necessary to estimate the behavior of the debris flow. The objective of this study is to evaluate the shear strength and rheological properties using the direct shear apparatus. The direct shear tests are conducted for two kinds of fine-grained soil specimens, which are in dry state and liquid limit state. From the direct shear tests, shear strengths are measured according to the normal stresses applied on the specimens to evaluate the cohesion and internal friction angle. In addition, reversal shear tests are performed for the fine-grained soil specimens in liquid limit state according to the shear rate to evaluate the residual shear strength. The results of direct shear tests show that the specimen at the liquid limit state has lower internal friction angle and higher cohesion compared to the dry stated, and the residual friction angle and cohesion at the residual state are lower than those at the peak state. In the result of reversal shear test, the residual shear strength is directly proportional to the shear rate and viscosity is calculated as $73.60Pa{\cdot}s$. This study demonstrates that the direct shear apparatus can be effectively used for the evaluation of the shear strength and rheological properties of the fine-grained soils related with the debris flow.

• Proceedings of the KSR Conference
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• 2001.10a
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• pp.558-561
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• 2001

SIP(Soil cement Injected Precast pile) that inserts a precast pile after injecting a cement paste into a boring has been applied rapidly through the change of construction circumstances. But there isnt any logical equation of a bearing capacity fitted to SIP yet. So Meyerhof equation has mainly been used to predict a bearing capacity in a design stage instead. But it has shortcomings such as lack of confidence because it has derived not from a theory but from an experience obtained from the result of SPT (Standard Penetration Test) and because a penetration depth tends to be deeper by an excessive design that depends on an end bearing capacity of a pile more than a skin frictional resistance. In this study, thereupon, a direct shear test in the laboratory was performed to both SM and SC soils in variable conditions to verify skin friction properties for the purpose of presenting some reasons capable of reducing penetration depths. Through the tests, soil to soil of SM in cohesion, rough panel to soil of SM in friction angle and soil to soil of SM in shear strength tended to be high. And a shear strength increased as its total unit weight increased in all cases.

• Geomechanics and Engineering
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• v.20 no.4
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• pp.299-312
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• 2020

The aim of this paper was to investigating the effects of soil relative density, construction materials roughness, oil type (gasoil, crude oil, and used motor oil), and oil content on the internal and interface shear behavior of sand with different construction materials by means of a modified large direct shear test apparatus. Tests conducted on the soil-soil (S-S), soil-rough concrete (S-RC), soil-smooth concrete (S-SC), and soil-steel (S-ST) interfaces and results showed that the shear strength of S-S interface is always higher than the soil-material interfaces. Internal and interface friction angles of sand beds increased by increase in relative density and decreased by increasing oil content. The oil properties (especially viscosity) played a major role in interface friction behavior. Despite the friction angles of contaminated sands with viscous fluids drastically decreased, it compensated by the apparent cohesion and adhesion developed between the soil grains and construction materials.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.39-54
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• 2009

Large scale direct shear tests were carried out to analyze the shear behavior of crushed rocks at local representative quarries. Shear strength for each specimen was derived and the effects on shear behavior induced by the variation of factors such as particle size, water immersion, density, uniformity coefficient, and particle breakage were evaluated and quantitatively compared with previous studies. The opportunity was also taken to identify stress-dilatancy relation of crushed rocks following the energy-based theory and friction coefficients at critical state as well as peak friction angles and dilation angles were estimated. As a result of tests it was found that uniaxial compressive strength and particle breakage of the parent rocks have crucial effect on internal friction angles; in addition, dilatancy at the failure showed strong relationship as well.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.387-398
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• 2018

The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.

• The Journal of Engineering Geology
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• v.9 no.1
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• pp.69-82
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• 1999

Direct shear tests are perfromed for artifical joint models made of cement with 25 types of different strength and roughness. The tests consist of the multi-stage test which is a common test method for a single joint plane and the test method suggested by ISRM. Then, not only the differences of friction angles between the two test methods are compared, but is the effectiveness of the multi-stage test investigated. The average of friction angles measured from the multi-stage test is $6.4^{\circ}$ lower than that from the ISRM test. Although the strength and roughness of samples vary, the differences of friction angles between the two test methods are constant. The relationship between the shear stress and the normal stress measured from the multi-stage test is well correlate with the Patton's equation. Whereas, the Barton's equation is best fitted with those measured from ISRM test.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.399-415
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• 2017

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.583-588
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• 2002

As environmental problem in course of construction has been a matter of interest, noise and vibration in the process of piling are considered as a serious problem. For this reason, the use of SIP method inserting pile as soon as boring and cement grouting is rapidly increasing for preventing vibration and noise. But a resonable bearing capacity formula for SIP method does not exit and even the standard specification for domestic condition isn't formed, though the lateral friction between cement paste and the ground does an important role and boring depth largely influences to the design bearing capacity, applying the SIP method . Therefore, the lateral friction was analyzed after the direct shear test worked with the lateral face of SIP and the soil.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.2
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• pp.101-111
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• 2021

Two different types of shear-friction tests were classified by external loadings and referred to as a push-off and a pull-off test. In a pull-off test, a tension force is applied in the transverse direction of the test specimen to produce a shear stress at the shear plane. This paper presents a method to evaluate shear transfer strengths of uncracked pull-off specimens. The method is based on the compression field theory and different constitutive laws are applied in some ways to gain accurate shear strengths considering softening effects of concrete struts based on Modified Compression Field Theory (MCFT) and Softened Truss Model (STM). The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with the predicted values. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked pull-off test specimens. A shear strength evaluation formula considering the effective compressive strength of a concrete strut was proposed, and the applicability of the proposed formula was verified by comparing with the experimental results in the literature.