• Journal of the Korean Geotechnical Society
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• v.34 no.6
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• pp.61-73
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• 2018

When the shear deformation occurs on the slope reinforced with soil nail, a passive earth pressure is induced on the ground around the soil nail and the increase of shear deformation causes the earth pressure variation of the ground and the deformation and member force change of the soil nail. In this study, the shear behavior of the soil nail was analyzed experimentally by inducing the shear deformation in the vertical direction of the soil nail using a large-scale direct shear test equipment and it was verified through numerical analysis. The shear test was performed on the bonded length (6D, 8D, 10D and 12D) of the soil nail separated from the shear surface. As a result, it was observed that the continuous increase of the shear deformation caused the damage of the grout and the effect according to the bonded length was analyzed. Through the model test and the numerical analysis, it was confirmed that the transfer length of the soil nail was 0.2~0.22m, which is larger than 0.1m suggested in the previous study, and the shear zone was in the range of 0.6m from the shear surface.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.156-161
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• 2003

Mechanical behavior of rock joints usually can be characterized by small-scale laboratory shear tests due to economical and technical limitations, but their applicability to the behaviour of rock mass has been always questioned by a number of researchers because of scale effect. Though there have been several researches regarding the scale effect, it has been a controversial problem how to apply the result of small-scale laboratory shear test directly to field design from different conclusions among researchers. In order to grasp the trend of scale effect of shear behavior, a series of direct shear tests on replicas of natural rock joint surfaces made of gypsum cement with different size and roughness were conducted and analyzed. Result showed that as the size of the specimen increased, average peak shear displacement increased, but average shear stiffness and average peak dilation angle decreased. As for the dependency of scale on shear strength, the degree of scale effect was dependent on normal stress and roughness of rock joint. For the condition of low normal stress and high roughness, decrease of average peak shear strength with increasing size of joint was evident.

• Tunnel and Underground Space
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• v.33 no.1
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• pp.10-28
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• 2023

Long-term shear behavior of the rock discontinuities should be analyzed and its stability should be evaluated to ensure the long-term stability of a high-level radioactive waste disposal repository. The long-term shear behavior of the discontinuities can be modeled with creep and RSF models. The shear creep test, velocity step test, and slide-hold-slide test can be performed to determine their model parameters or analyze the shear behavior by experiments under various conditions. Testing apparatuses for direct shear, triaxial compression, and biaxial shear were mainly used and improved to reproduce the thermo-hydro-mechanical conditions of local bedrock, and it was confirmed that the shear behavior could vary. In order to design a high-level radioactive waste disposal site in Korea, the long-term behavior of rock discontinuities should be investigated in consideration of rock types, thermo-hydro-mechanical conditions, metamorphism, and restoration of shear resistance.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.65-72
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• 2007

Large-scale direct shear tests were conducted in order to investigate both the shear strength of soil itself and the friction behavior at the interface of soil/geosynthetics in respect of efficiency in this study. Sand, crushed stone and three types of geotextile (i.e. one woven geotextile and two nonwoven geotextiles) were used in the experimental program. The considered interfaces for the evaluation of interface shear strength in this study included sand/sand, crushed stone/crushed stone, sand/woven geotextile, crushed stone/woven geotextile, crushed stone/nonwoven geotextile-A and crushed stone/nonwoven geotextile-B. The results showed that the efficiency of 84% was obtained at the interface of sand/woven geotextile compared with the shear strength of sand itself (i.e. sand/sand interface). The efficiencies of 74%, 83% and 72% were obtained at the interface of crushed stone/nonwoven geotextile-A, crushed stone/nonwoven geotextile-B and crushed stone/woven geotextile, respectively compared with the shear strength of crushed stone itself (i.e. crushed stone/crushed stone interface).

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.136-145
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• 2009

Factors influencing shear behavior of granular material include particle size, shape, distribution, relative density, particle crushing, etc. In this study, these factors are characterized by viewpoint of shear behavior using numerical analysis based on DEM. Geometrical particle shape is represented by a combination of small circular particles and influence of particle shape on crushing is studied through relative comparisons between clump (uncrushable) and cluster (crushable) models which are modeled using DEM. Also, particle shape is quantified by the dimensionless parameters such as circularity and convexity. The results indicate that particle shape indexes have a negative association with internal friction angle. Also, internal friction angle becomes reduced and failure envelop curve becomes nonlinear due to the particle crushing. It is also found that numerical results are quite good agreement with the experimental test conducted in this study.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.574-593
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• 2023

In this study, the effectiveness and applicability of a newly designed Compact CNS shear box for conducting direct shear tests on jointed rock specimens were investigated. CNS joint shear tests were conducted on jointed rocks with Artificially generated roughness while varying the fracture surface roughness coefficient and initial normal stress conditions. In addition, displacement data were validated by Digital image correlation analysis, fracture patterns were observed, and comparative analysis was conducted with previously studied shear behavior prediction models. Furthermore, the accuracy of the displacement data was confirmed through DIC analysis, the fracture patterns were observed, and the shear properties obtained from the tests were compared with existing models that predict shear behavior. The findings exhibited a strong correlation with specific established empirical models for predicting shear behavior. Furthermore, the potential linkage between the characteristics of shear behavior and fracture patterns was deliberated. In conclusion, the CNS shear box was shown to be applicable and effective in providing data on the shear characteristics of the joint.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.201-207
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• 2002

An advanced fiber sheet has been widely used for strengthening of the concrete structures due to its excellent properties such as high strength and light weight. Bond strength is very important in strengthening the concrete structures using an advanced fiber sheet. This research examines the bond behavior between fiber sheet and concrete, investigates the bond strength by the direct pull-out test and the tensile-shear test. To obtain the tensile-shear strength a double-face shear type bond test is conducted. The primary test variables are the types of concrete surface roughness (disk-grinding/chipping) and retrofitting methods (bonding/injection). Thirty specimens were tested to evaluate the bond strength. It is shown that the average bond strength between fiber sheet and concrete by the direct pull-out test and the tensile-shear test is $22.3{\sim}23.1kgf/cm^2$ $17.92{\sim}19.75kgf/cm^2$, respectively.

• Geomechanics and Engineering
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• v.12 no.2
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• pp.211-221
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• 2017

A laboratory investigation into crude oil contaminated sand-concrete interface behavior is performed. The interface tests were carried out through a direct shear apparatus. Pure sand and sand-bentonite mixture with different crude oil contents and three concrete surfaces of different textures (smooth, semi-rough, and rough) were examined. The experimental results showed that the concrete surface texture is an effective factor in soil-concrete interface shear strength. The interface shear strength of the rough concrete surface was found higher than smooth and semi-rough concrete surfaces. In addition to the texture, the normal stress and the crude oil content also play important roles in interface shear strength. Moreover, the friction angle decreases with increasing crude oil content due to increase of oil concentration in soil and it increases with increasing interface roughness.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.31-41
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• 2006

The scale effect of specimens on the shear behavior of joints is studied by performing direct shear tests on six different sizes in Granite. The peak and residual shear stress, shear displacement, shear stiffness, and dilation angle are measured with the different normal stress(0.29~2.65MPa) and roughness parameters. It is also shown that both the joint roughness coefficient(JRC) and the joint compression strength(JCS) reduce with increasing joint length. A series of shear tests show about 56~67% reduction in peak shear stress, and about 18~44% in residual shear stress, respectively as the contact area of joint increases from 12.25 to $361cm^2$. Also the variation of dilation angle is $27^{\circ}$ at normal stress of 0.29 MPa and $6^{\circ}$ at normal stress of 2.65 MPa, respectively. The envelopes considering scale effect for JRC are made for the peak shear strength of rock joint in comparison with the Barton's equation.

• Geomechanics and Engineering
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• v.28 no.5
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• pp.505-520
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• 2022

In recent years, geotextile-encased gravel columns (usually called stone columns) have become a popular method to increasing soil shear strength, decreasing the settlement, acceleration of the rate of consolidation, reducing the liquefaction potential and increasing the bearing capacity of foundations. The behavior of improved loose base-soil with gravel columns under shear loading and the shear stress-horizontal displacement curves got from large scale direct shear test are of great importance in understanding the performance of this method. In the present study, by performing 36 large-scale direct shear tests on sandy base-soil with different fine-content of zero to 30% in both not improved and improved with gravel columns, the effect of the presence of gravel columns in the loose soils were investigated. The results were used to predict the shear stress-horizontal displacement curve of these samples using support vector machines (SVM). Variables such as the non-plastic fine content of base-soil (FC), the area replacement ratio of the gravel column (Arr), the geotextile encasement and the normal stress on the sample were effective factors in the shear stress-horizontal displacement curve of the samples. The training and testing data of the model showed higher power of SVM compared to multilayer perceptron (MLP) neural network in predicting shear stress-horizontal displacement curve. After ensuring the accuracy of the model evaluation, by introducing different samples to the model, the effect of different variables on the maximum shear stress of the samples was investigated. The results showed that by adding a gravel column and increasing the Arr, the friction angle (ϕ) and cohesion (c) of the samples increase. This increase is less in base-soil with more FC, and in a proportion of the same Arr, with increasing FC, internal friction angle and cohesion decreases.