• 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.

• Tunnel and Underground Space
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• v.17 no.3 s.68
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• pp.203-215
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• 2007

Stability and mechanical deformation behavior of rock masses are highly dependent on the mechanical characteristics of contained discontinuities. Therefore, mechanical characteristics of the discontinuities should be considered in the design of tunnel and underground structures. In this study, direct shear tests for rough granite joints were carried out under constant normal stiffness conditions. Effects of initial normal stress, shear velocity, and surface roughness on the characteristics of shear strength and deformation behaviors were examined. Results of shear testing under constant normal stiffness conditions reveal that shear behaviors could be classified into two categories, based on the amount of decrease in shear stress at the Int peak shear stress. With initial normal stiffness increasing, it turned out that shear displacement at peak stress and the first peak shear stress increased, however friction angle and friction coefficient showed decrease. In case of shear stiffness and average friction coefficient, it turned out that they are not dependent on the initial normal stress. Minor effects of shear velocity on rough joints were observed in several shear quantities. However, the effects of shear velocity were insignificant regardless of the normal stress increase. Change of shear strength and deformation characteristics on joint roughness were examined, however, it turned out that the variations were attributed to deviation of shear test specimens.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.23-35
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• 2006

Shear load transfer characteristics of rock-socketed drilled shafts were analyzed. The constant normal stiffness (CNS) direct shear tests were performed to identify the major influencing factors of shaft resistance, i.e., unconfined compressive strength, borehole roughness, normal stiffness, initial confining stress, and material properties. Based on the CNS tests, shear load transfer function of drilled shafts in rocks is proposed using borehole roughness and the geological strength index (GSI), which indicates discontinuity and surface condition of rock mass in Hoek-Brown criterion (1997). The proposed load-transfer function was verified by the load test results of seven rock-socketed drilled test shafts subjected to axial loads. Through comparisons of the results of load tests, it is found that the load-transfer function by the present study is in good agreement with the general trend observed by in situ measurements, and thus represents a significant improvement in the prediction of load transfer of drilled shafts.