• The Journal of Engineering Geology
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• v.30 no.1
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• pp.85-101
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• 2020

The estimation of strength parameters is very important for the stability analysis of rock slopes. Various methods for the determination of strength parameters were suggested by various researchers. The number of methods used for the estimation of strength parameters in the stability analysis of rock slopes were investigated based on literature reviews. The frequency of the method determining strength parameters were investigated with respect to failure types. The cohesion and friction angles of the rock and discontinuities are presented with RMR values. The cohesion shows wider range of values relative to those of friction angles according to current studies. Even though RMR does not show any correlation with cohesion values, RMR and the friction angle of the rock clearly shows a positive relationship. Proper methods should be utilized for the determination of strength parameters with consideration for failure types and be proved through literature reviews. The credibility of determining strength parameters is expected to improve if strength parameters data are accumulated from the back analysis performed for failed local rock slopes.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.177-189
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• 2009

The shear strength has been managed as an important factor in soil mechanics. The shear strength estimation model was developed to evaluate the shear strength using only a few soil properties by the linear regression analysis model which is one of the statistical methods. The shear strength is divided into two part; one is the internal friction angle (${\phi}$) and the other is the cohesion (c). Therefore, some valid soil factors among the results of soil tests are selected through the correlation analysis using SPSS and then the model are formulated by the linear regression analysis based on the relationship between factors. Also, the developed model is compared with the result of direct shear test to prove the rationality of model. As the results of analysis about relationship between soil properties and shear strength, the internal friction angle is highly influenced by the void ratio and the dry unit weight and the cohesion is mainly influenced by the void ratio, the dry unit weight and the plastic index. Meanwhile, the shear strength estimated by the developed model is similar with that of the direct shear test. Therefore, the developed model may be used to estimate the shear strength of soils in the same condition of study area.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.1
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• pp.51-61
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• 2005

In general the strength parameter of the ground will be changed by reinforcing the ground around tunnel. In this case, the concept of tunnel design, such as supporting system, excavation, lining and so on, should be modified based on the failure criteria or the ground changed by the reinforcement. This paper presents the variation mechanism of strength parameters and new failure criteria of the reinforced ground. In order to perform this research, theoretical and experimental works were carried out. It was clearly founded that the cohesion of strength parameters is only increased by reinforcement of ground, especially by rock bolting.

• 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.

• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.5-19
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• 2019

Considering the natural phenomenon in which steep slopes ($65^{\circ}{\sim}85^{\circ}$) consisting of rock mass remain stable for decades, slopes steeper than 1:0.5 (the standard of slope angle for blast rock) may be applied in geotechnical conditions which are similar to those above at the design and initial construction stages. In the process of analysing the stability of a good to fair continuum rock slope that can be designed as a steep slope, a general method of estimating rock mass strength properties from design practice perspective was required. Practical and genealized engineering methods of determining the properties of a rock mass are important for a good continuum rock slope that can be designed as a steep slope. The Genealized Hoek-Brown (H-B) failure criterion and GSI (Geological Strength Index), which were revised and supplemented by Hoek et al. (2002), were assessed as rock mass characterization systems fully taking into account the effects of discontinuities, and were widely utilized as a method for calculating equivalent Mohr-Coulomb shear strength (balancing the areas) according to stress changes. The concept of calculating equivalent M-C shear strength according to the change of confining stress range was proposed, and on a slope, the equivalent shear strength changes sensitively with changes in the maximum confining stress (${{\sigma}^{\prime}}_{3max}$ or normal stress), making it difficult to use it in practical design. In this study, the method of estimating the strength properties (an iso-angle division method) that can be applied universally within the maximum confining stress range for a good to fair continuum rock mass slope is proposed by applying the H-B failure criterion. In order to assess the validity and applicability of the proposed method of estimating the shear strength (A), the rock slope, which is a study object, was selected as the type of rock (igneous, metamorphic, sedimentary) on the steep slope near the existing working design site. It is compared and analyzed with the equivalent M-C shear strength (balancing the areas) proposed by Hoek. The equivalent M-C shear strength of the balancing the areas method and iso-angle division method was estimated using the RocLab program (geotechnical properties calculation software based on the H-B failure criterion (2002)) by using the basic data of the laboratory rock triaxial compression test at the existing working design site and the face mapping of discontinuities on the rock slope of study area. The calculated equivalent M-C shear strength of the balancing the areas method was interlinked to show very large or small cohesion and internal friction angles (generally, greater than $45^{\circ}$). The equivalent M-C shear strength of the iso-angle division is in-between the equivalent M-C shear properties of the balancing the areas, and the internal friction angles show a range of $30^{\circ}$ to $42^{\circ}$. We compared and analyzed the shear strength (A) of the iso-angle division method at the study area with the shear strength (B) of the existing working design site with similar or the same grade RMR each other. The application of the proposed iso-angle division method was indirectly evaluated through the results of the stability analysis (limit equilibrium analysis and finite element analysis) applied with these the strength properties. The difference between A and B of the shear strength is about 10%. LEM results (in wet condition) showed that Fs (A) = 14.08~58.22 (average 32.9) and Fs (B) = 18.39~60.04 (average 32.2), which were similar in accordance with the same rock types. As a result of FEM, displacement (A) = 0.13~0.65 mm (average 0.27 mm) and displacement (B) = 0.14~1.07 mm (average 0.37 mm). Using the GSI and Hoek-Brown failure criterion, the significant result could be identified in the application evaluation. Therefore, the strength properties of rock mass estimated by the iso-angle division method could be applied with practical shear strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.147-154
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• 2008

Weathered soil slope loses its shear strength if it is exposed in the air for a long time or in contact with water. And this kind of strength loss is remarkable in dam slope which has very big difference in water level according to the season. In this study, shear strength loss of weathered soil due to saturation had been found out through dryness and wetness repetition direct shear test. Also relation between penetration blow number(Nc) and shear strength parameter had been found out through small sized dynamic cone penetration test device and the correlation equation of Nc had been proposed through artificial neural network analysis to estimate shear strength parameter easily.

• Journal of the Korean Geosynthetics Society
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• v.8 no.3
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• pp.25-34
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• 2009

Determination of design parameters of composite ground including colluvial soil layer is far difficult because the maximum particle size of such a soil is remarkably large and particle distribution may vary from area to area. The stress-strain behavior of colluvial soils is in fact dependent upon the engineering characteristics at the boundary between coarse and fine materials. However, strength parameters are in general determined based on the characteristics of fine material, which causes an underestimation of such parameters. In this study, strength parameters of colluvial soil are evaluated by means of BIMROCK model curve. In addition, limit equilibrium analysis is carried out to verify the rational shear strength evaluation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.195-202
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• 1994

In this research, a lot of triaxial test results (CID) are analyzed to study the curvature characteristics of failure envelope of sand and parametric relationship between shear strength and state parameter by Been and Jefferies. In the conventional triaxial tests, correction for the change of sectional area of a sample and for membrane influence is essential especially in order to determine critical state (or steady state) condition more correctly. Based on the test results, a model to express the shear strength of fine sand as a function of density and stress level is presented and curvature characteristics of shear failure envelope and parametric relationship between state parameter and shear strength parameters are evaluated.

• Journal of the Korean GEO-environmental Society
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• v.13 no.8
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• pp.75-84
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• 2012

In this paper, strength and leaching characteristics of water sludge-added lightweight soils(WALS) considering reinforcing materials(waste fishing net, glue treated waste fishing net and geogrid) and layer(1 or 2 layer) were investigated using unconfined compression test and leaching test. Several specimens of water sludge-added lightweight soil consisted of water sludge, cement, and bottom ash were prepared according to flowability. Reinforcing material added into these specimens were waste fishing net and geogrid. A glue treated waste fishing net was also added in order to increase interlocking between soil mixture and waste fishing net. Strength increased in the order of WALS reinforced by waste fishing net, glue treated waste fishing net, and geogrid. Strength of specimen with double layer-reinforcing material was greater than that of specimen with single layer reinforcing material. Leaching result of WALS was also satisfied with standard of ministry of environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.529-535
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• 2016

In this theoretical study, the strength parameters of the Drucker-Prager yield criterion and Mohr-Coulomb yield criterion were set to equal values, in order to analyze the correlation among the parameters. The Drucker-Prager strength parameters ${\alpha}$ and k were represented by the Mohr-Coulomb strength parameters c and ${\phi}$. Specifically it can be seen that k is function of c, ${\phi}$ and ${\alpha}$ is function of ${\phi}$ alone. Drucker-Prager strength parameter ${\alpha}$ increases as the internal friction angle of soil increases. ${\alpha}_{av}$ which is the average of ${\alpha}_c$ and ${\alpha}_i$ was proportional to internal friction angle in which ${\alpha}_c$ and ${\alpha}_i$ are ${\alpha}$ values corresponding to the circles of the Drucker-Prager yield cirteria circumscribes and inscribes the Mohr-Coulomb yield criterion respectively. The values of the ${\alpha}_{av}$ was 0.07 and 0.29 which correspond to the internal friction angle of $10^{\circ}$ and $45^{\circ}$ respectively. In addition, value of ${\alpha}_c/{\alpha}_i$ was proportional to internal friction angle of soil and the values of ${\alpha}_c/{\alpha}_i$ 1.12 and 1.62 which corresponds to internal friction angle of $10^{\circ}$ and $45^{\circ}$ respectively.The influence of the Mohr-Coulomb strength parameters on the Drucker-Prager strength parameter k was investigated and it was found that k was mainly influenced by the cohesion of the soil, except in the case of the minimum assumed value of c of 10kPa. The deviator stresses, $S_{c0}$ and $S_{t0}$, which correspond to the cases of the Mohr-Coulomb yield criterion under uniaxial compression and uniaxial tension, respectively, and $S_{0(ave)}$, which is the average value of $S_{c0}$ and $S_{t0}$, decrease as the internal friction angle increases. Furthermore, the hexagon, which represents the Mohr-Coulomb yield locus, becomes more irregular, and the deviations of $S_{c0}$ and $S_{t0}$ from $S_{0(ave)}$ also increase, as the internal friction angle increases.