• Tunnel and Underground Space
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• v.22 no.6
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• pp.462-470
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• 2012

Implementing the generalized Hoek-Brown failure criterion in the framework of the Mohr-Coulomb criterion requires the calculation of the equivalent friction angle and cohesion. In the conventional method based on the Balmer (1952)'s theory, the tangential instantaneous friction angle and cohesion are expressed in terms of the minimum principal stress ${\sigma}_3$, which does not provide the information about the dependency of the equivalent parameters on the hydrostatic pressure and the stress path. In this study, this defect of the conventional method has been overcome by representing the equivalent parameters in terms of stress invariants. Through the example implementation of the new method, the influence of the magnitude of the hydrostatic pressure and the Lode angle on the tangential instantaneous friction angle and cohesion is investigated. It turns out that the tangential instantaneous friction angle is maximum when the stress condition is triaxial extension, while the tangential cohesion is maximum when the stress condition is triaxial compression. The dependency of the equivalent Mohr-Coulomb strength parameters on the hydrostatic pressure and the Lode angle tends to be more substantial for the favorable rockmass of larger GSI value.

• Tunnel and Underground Space
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• v.25 no.3
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• pp.284-292
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• 2015

The generalized Hoek-Brown failure criterion, the strength parameters of which are determined by using the GSI index, is an empirical nonlinear failure criterion of rock mass and has been widely employed in various rock engineering practices. Many rock engineering practitioners, however, are still familiar with the description of the strength of rock mass in terms of friction angle and cohesion. In addition, almost all rock mechanics softwares incorporate the simple linear Mohr-Coulomb function. Therefore, it is necessary to provide a tool to implement the Hoek-Brown function in the framework of the Mohr-Coulomb criterion. In this study, the use of upper-bound solution of limit analysis for bearing capacity of a strip footing resting on the ground surface is proposed for the estimation of the equivalent friction angle and cohesion of rock mass incorporating the generalized Hoek-Brown failure criterion. The upper-bound bearing capacity is expressed in terms of friction angle by use of the relationship between tangential friction angle and tangential cohesion implied in the generalized Hoek-Brown function. The friction angle minimizing the upper-bound bearing capacity is taken as the equivalent friction angle. Through the illustrative implementations of the proposed method, the influences of GSI, $m_i$ and D on the equivalent friction angle and cohesion are investigated.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.172-183
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• 2019

The generalized Hoek-Brown (GHB) failure criterion developed by Hoek et al. (2002) is a nonlinear function which defines a stress condition at failure of rock mass. The relevant strength parameter values are systematically determined using the GSI value. Since GSI index is a value quantifying the condition of in-situ rock mass, the GHB criterion is a practical failure condition which can take into the consideration of in-situ rock mass quality. Considering that most rock mechanics engineers are familiar with the linear Mohr-Coulomb criterion and that many rock engineering softwares incorporate Mohr-Coulomb criterion, the equations for the equivalent friction angle and cohesion were also proposed along with the release of the GHB criterion. The proposed equations, however, fix the lower limit of the minor principal stress range, where the linear best-fitting is performed, with the tensile strength of the rock mass. Therefore, if the tensile stress is not expected in the domain of analysis, the calculated equivalent friction angle and cohesion based on the equations in Hoek et al. (2002) could be less accurate. In order to overcome this disadvantage of the existing equations for equivalent friction angle and cohesion, this study proposes the analytical formula which can calculate optimal equivalent friction angle and cohesion in any minor principal stress interval, and verified the accuracy of the derived formula.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.27-37
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• 2003

In this research stress-strain behavior of composite geocell-soil systems under triaxial condition and the influence of strength due to the presence of geocell were studied. For the research a series of triaxial tests were carried out on sand specimens confined by flexible-walled single rubber cell. The diameter of all rubber cells placed at the center of the soil sample were 50 mm. Three rubber sizes, i.e. 35, 50 and 70 mm height, were applied to the soil specimen and the size of soil specimen was 50 mm in diameter and 100 mm in height. Three different densities of soil were used for the tests. In general, it was observed that the sand specimen develops an apparent cohesion due to the confinement by the geocell. The magnitude of this cohesion seemed to be dependent to the properties of the geocell material. The test results have shown that the geocell material for this research not only develops the apparent cohesion but also increases the angle of friction whereas geosynthetic material in the references showed only the increase of apparent cohesion. From the application of geocell-soil composites to the hyperbolic model, it was recognized that the determination of the peak strength influences the behavior of the geocell-soil composites.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.1
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• pp.206-217
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• 2001

The purpose of this study was to estimate that the relations of weathering speed and shear strength of granite soil by tracing the weathering depth of granite soil from the very moment of its cutting. The results obtained this follows ; 1) The relationships among Nc, Li and CEC, Li>6%, CEC>14 corresponds to Nc=2~30, and 4%${\phi}$)increases at a standard pressure. 3) And Nc=0~50 corresponds to $27{\sim}50^{\circ}$ of internal fiction angle and to 12~49kPa of cohesion. That is to say, internal friction angle(${\phi}$)corresponds better than cohesion(c). In conclusion, this study suggests that in simplified dynamic cone penetration test a penetration boundary line of 5 centimeters is decided at around Li=4%, CEC=3(meq/100g) which is classified as a completely weathering soil. It also appears that CEC increases as Li increases while Nc decreases.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.219-227
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• 2013

Although Mohr-Coulomb failure criterion has limitations in that it is a linear criterion and the effect of the intermediate principal stress on failure is ignored, this criterion has been widely accepted in rock mechanics design. In order to overcome these shortcomings, the Hoek-Brown failure criterion was introduced and recently a number of 3-D failure criteria incorporating the effect of the intermediate principal stress on failure have been proposed. However, in many rock mechanics designs, the possible failure of rock mass is still evaluated based on Mohr-Coulomb criterion and most of practitioners are accustomed to understanding the strength of rock mass in terms of the internal friction angle and cohesion. Therefore, if the equivalent Mohr-Coulomb strength parameters of the advanced failure criteria are calculated, it is possible to take advantage of the advanced failure criteria in the framework of the Mohr-Coulomb criterion. In this study, a method expressing the tangential Mohr-Coulomb strength parameters in terms of the stress invariant is proposed and it is applied to the generalized Hoek-Brown criterion and the HB-WW criterion. In addition, a new approach describing the geometric meaning of the ${\sigma}_2$-dependency of failure criteria in 3-D principal stress space is proposed. Implementation examples of the proposed method show that the influence of the intermediate principal stress on the tangential friction angle and cohesion of the HB-WW criterion is considerable, which is not the case for the 2-D failure criterion.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1093-1097
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• 1996

The Substitution development of 7075-T6 Al alloy to 7050-T74 Al alloy in small arms to improve anti-stress corrosion cracking was processed along with mass productivity consideration. To meet 7050 Al alloy material characteristics Indirect extrusion type was adopted and local heating above recrystalization temperature in forging process had to be avoided. The T74 aging treatment was 12$0^{\circ}C$ -6hrs and 175$^{\circ}C$ -12hrs and was appropriate for both machanical and anti-cohesion properties. In accessment of field application test 7050Al alloy made parts of small arms showed equivalent or better performance than 7075 Al alloy.

• Korean Journal of Construction Engineering and Management
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• v.10 no.4
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• pp.151-164
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• 2009

Strategic alliances developed as formalized inter-organizational relationships are core vehicles to share information, resources and knowledge. The structural characteristics of strategic network constructed by strategic alliances have been important agenda in strategic management discipline. This paper has two folds in analysing the strategic network formulated by project level alliances in Korean construction industry. First, we investigate the strategic network using the tools and methods of social network analysis, such as centrality, cohesion, structural equivalence, and power law. Second, the performance of firms within networks are analysed longitudinally with panel data analysis. We have found that the strategic networks in this industry has scale-free characteristics, where the degree distribution fits the power law, and the vertically equivalent structure is clear. We also present that the performance of firms are continuously affected by the degree centrality of firms in this network for the last 10 years.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.480-493
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• 2021

Since the generalized Hoek-Brown criterion (GHB) provides an efficient way of identifying its strength parameter values with the consideration of in-situ rock mass condition via Geological Strength Index (GSI), this criterion is recognized as one of the standard rock mass failure criteria in rock mechanics community. However, the nonlinear form of the GHB criterion makes its mathematical treatment inconvenient and limits the scope of its application. As an effort to overcome this disadvantage of the GHB criterion, the explicit approximate analytical equations for the minimum principal stress, which is associated with the maximum principal stress at failure, are formulated based on the Taylor polynomial approximation of the original GHB criterion. The accuracy of the derived approximate formula for the minimum principal stress is verified by comparing the resulting approximate minimum principal stress with the numerically calculated exact values. To provide an application example of the approximate formulation, the equivalent friction angle and cohesion for the expected plastic zone around a circular tunnel in a GHB rock mass are calculated by incorporating the formula for the approximate minimum principal stress. It is found that the simultaneous consideration of the values of mi, GSI and far-field stress is important for the accurate calculation of equivalent Mohr-Coulomb parameter values of the plastic zone.

• The Journal of the Convergence on Culture Technology
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• v.8 no.2
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• pp.83-89
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• 2022

Recentely, the military needs to apply various technologies for the improvement of teamwork. The government should take the non-face-to-face system due to the social interest of young military members. In this study we investigated collective cohesion by helping soldiers who have difficulty expressing their feelings and delivering messages while living in groups, or who are unable to adapt to group life due to psychological disorders such as relationship anxiety. We proposed the Multi-perspective Relationship Experience program as a new VR application. We showed feeling a sense of reality equivalent to the actual situation, interpersonal tension and social distance were significantly reduced, and communication, which was difficult to actually do, was naturally achieved. In addition, positive effects were confirmed on the sense of belonging and leadership among all participants. We will be effectively used in manpower management policies that improve the collective cohesion of soldiers and support the adaptability of the military environment in line with the rapidly changing social interaction method.