• Journal of the Korean Geotechnical Society
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• v.32 no.3
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• pp.15-27
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• 2016

In this study, a series of triaxial compressive strength tests were conducted for basaltic intact rocks sampled in the northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island. Hoek-Brown constants $m_i$ were estimated from the results of the triaxial compression tests, and the properties of the Hoek-Brown constants $m_i$ were investigated. In addition, the cohesion and internal friction angle, strength parameters of Mohr-Coulomb failure criterion, obtained from the results of the triaxial compression tests were compared and analyzed with those estimated from Hoek-Brown failure criterion, respectively. As results, it was found that the Hoek-Brown constant $m_i$ is deeply related to the internal friction angle. As the internal friction grows, the Hoek-Brown constant $m_i$ increases exponentially. The cohesions estimated from the Hoek-Brown failure criterion, on average, are approximately 24% higher than those obtained from the Mohr-Coulomb failure criterion. The internal friction angles estimated from the Hoek-Brown failure criterion are similar to those obtained from the Mohr-Coulomb failure criterion.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.77-91
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• 2003

The Hoek-Brown failure criterion for rock masses developed first in 1980 is widely accepted and has been applied in a variety of rock engineering problems including slope analyses. The failure criterion was modified over the years because rock mass strength by the original failure criterion in 1980 was overestimated. The modified failure criterion, named Generalized Hoek-Brown Failure Criterion, was proposed with a new classification called the Geological Strength Index(GSI) in 1994. Generally, Hoek-Brown failure criterion is applied in numerical analyses of rock mass behaviors using equivalent Mohr-Coulomb parameters estimated by linear regression method. But these parameters estimated by this method have some inaccuracies to be applied and to be incorporated into numerical models and limit equilibrium programs. The most important issue is that this method cannot take account of non-linear characteristics of Hoek-Brown criterion, therefore, equivalent Mohr-Coulomb parameters is used as constant values regardless of field stress distribution in rock masses. In this study, the numerical analysis on rock slope stability considering non-linear characteristics of Hoek-Brown failure criterion was carried out. Futhermore, by the latest Hoek-Brown failure criterion in 2002, the revised estimating method of equivalent Mohr-Coulomb parameters was applied and rock mass damage criterion is introduced to account for the strength reduction due to stress relaxation and blast damge in slope stability.

• Geomechanics and Engineering
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• v.34 no.1
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• pp.69-86
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• 2023

To overcome the dilemma of the [BQ] method's inability to predict mountain tunnel support loads, this study is based on the Hoek-Brown criterion and previous results to obtain the connection equations from GSI scores to each parameter of the Hoek-Brown criterion and the link between the [BQ] scores and the GSI system. The equations were embedded in the Hoek-Brown criterion of FLAC6.0 software to obtain tunnel construction forecasts without destroying the in-situ stratigraphy. The feasibility of the secondary development of the Hoek-Brown criterion was verified through comparative analysis with field engineering measurements. If GSI > 45 with a confining pressure of less than 10 MPa, GSI has little effect on the critical softening factor while we should pay attention to the parameter of confining pressure when GSI < 45. The design values for each parameter are closer to the FLAC3D simulation results and the secondary development of the Hoek-Brown criterion meets the design objectives. If the Class V surrounding rock is thinned with shotcrete or the secondary lining is installed earlier, the secondary lining may act as the main load-bearing structure. The study may provide ideas for rapid prediction of mountainous tunnels in China.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.153-163
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• 2009

In this study, a series of triaxial tests on Jeju basalt were carried out and then rock strength parameters were estimated by the Mohr-Coulomb failure criterion and the Hoek-Brown failure criterion using the test results. The characteristics of both failure criterions were investigated through comparing the estimated rock strength parameters. As the result of the Mohr-Coulomb criterion, the cohesions and the internal friction angles are determined as 5.35 MPa and $50.25^{\circ}$ of Pyoseonri basalt, 16.99 MPa and $60.66^{\circ}$ of Trachy-basalt, and 2.33 MPa and $37.05^{\circ}$ of Scoria, respectively. The cohesions and internal friction angles were estimated by the Hoek-Brown failure criterion in the basis of the results of regression analysis. The cohesions and the internal friction angles are determined as 4.77 MPa and $52.47^{\circ}$ of Pyoseonri basalt, 14.69 MPa and $60.70^{\circ}$ of Trachy-basalt, and 2.22 MPa and $47.60^{\circ}$ of Scoria, respectively. As the result of comparison between the Mohr-Coulomb failure criterion and the failure envelope predicted by the Hoek-Brown criterion, the cohesion estimated by the Hoek-Brown criterion is usually lower than that obtained from the Mohr-Coulomb criterion, whereas the friction angle estimated by the Hoek-Brown criterion is higher than that obtained from the Mohr-Coulomb criterion.

• Journal of the Korean Geotechnical Society
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• v.30 no.3
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• pp.73-85
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• 2014

The strength parameters used in rock mass design are mainly estimated by equations using Hoek-Brown failure criterion because the tests to obtain the values are limited and expensive. To estimate the strength parameters, the Hoek-Brown failure criterion should be transformed to the Mohr-Coulomb failure criterion. But the processes are more or less cumbersome due to the several stages including the computation and the analyzing steps. In this study, several rock states of various conditions were modeled and then the strength parameters were estimated using the Hoek-Brown failure criterion. Thereafter by analyzing the results, some charts and equations estimating the strength parameters through only one step or easily in the field using the values of RMC, the uniaxial compressive strength and the rock constant ($m_i$), were suggested. And then the suggested method was compared and discussed with the existing method.

• Tunnel and Underground Space
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• v.24 no.4
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• pp.289-296
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• 2014

A simple analytical approach for stability assessment of underground storage caverns against ground uplift of overburden rock above the rock caverns for high pressurized fluid such as compressed air energy storage (CAES) and compressed natural gas (CNG) was developed. In the developed approach, we assumed that failure plane of the overburden is straight upward to ground surface, and factor of safety can be calculated from a limit equilibrium analysis in terms of this cylindrical shape failure model. The frictional resisting force on the failure plane was estimated by Hoek-Brown strength criterion which replaces with Mohr-Coulomb criterion such that both intact rock strength and rock mass conditions can be considered in the current approach. We carried out a parametric sensitivity analysis of strength parameters under various rock mass conditions and demonstrated that the factor of safety againt ground uplift was more sensitive to Mohr-Coulomb strength criterion rather than Hoek-Brown criterion.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.228-235
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• 2005

Friction angle and cohesion of rock masses can be estimated from Hoek and Brown failure criterion and then plastic corrections can be applied using Mohr-Coulomb yield function. This study finds that this estimation procedure would not be appropriate for weak rock masses and for cases where low confining stress is expected to develop. A procedure is outlined in this paper for estimating plastic corrections directly from Hoek and Brown material model. Comparative study shows that direct procedure would simulate non-linear failure surface better than indirect procedure especially in the low confining stress regime.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.81-88
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• 2014

In the course of performing the stability analysis of rock structures, there are times when the strength of the Hoek-Brown rock mass needs to be understood in terms of the internal friction angle and cohesion. In this case, the original Hoek-Brown criteion, giving the relationship between ${\sigma}_1$ and ${\sigma}_3$ at failure, have to be transformed to the corresponding Mohr envelope. A new approach to derive the Mohr envelope of the Hoek-Brown criterion is suggested in this study. The new method is based on the Londe's transformation making the stress components dimensionless. The correctness of the derivation leading to the new ${\tau}-{\sigma}$ relationship is confirmed by comparing the calculation results with the Bray's solution through a verification example.

• Geomechanics and Engineering
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• v.3 no.1
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• pp.61-81
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• 2011

In this paper, a complement to the Hoek-Brown criterion is proposed in order to derive the strength of anisotropic rock from strength of the corresponding truly intact rock. The complement is a decay function, which unlike other modifications or suggestions made in the past, is multiplied to the function of the original Hoek-Brown failure criterion for intact rock. This results in a combined and extended form of the criterion which describes the strength of anisotropic rock as a varying fraction of the corresponding truly intact rock strength. Statistical procedures and in particular regression analyses were conducted into data obtained in experiments conducted in the current research program and those collected from the literature in order to define the Hoek-Brown's criterion complement. The complement function was best described by a simple polynomial including only three constants to be empirically evaluated. Further investigations also showed that these constants can be related to the other readily available parameters of rock material which further facilitate determining the constants. A great and prime advantage of the proposed complement is that it is mathematically simple including the least possible number of empirical constants which are easily estimated with minimum experimental effort. Moreover, proposed concept does not suggests any change to the original Hoek-Brown criterion itself or its constants and serves whenever anisotropy does exist in the rock. This further implies on the possibility of using any other failure criterion for intact rock in conjunction with the compliment to reach the strength of anisotropic rock.

• 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.