• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.59-69
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• 2015

This study examined the magnitude and distribution of earth pressure on the support system in a jointed rock mass due to the different joint sets as well as varying the rock type and joint condition (joint shear strength and joint inclination angle). Based on a physical model test and its numerical simulation, a series of numerical parametric analyses were conducted using a discrete element method. The results showed that the induced earth pressure was affected significantly by a joint set depending on the inclusion of the joint inclination angle, which induces a joint sliding condition, but the number of joint sets alone was not important, even though the earth pressure could be increased slightly as the number of joint sets is increased. In addition, the study results were compared with Peck's earth pressure for soil ground, which indicated that the earth pressure in a jointed rock mass could be considerably different from that in soil ground. The study suggests that the effects of joint sets as well as rock type and joint condition are important factors affecting the earth pressure in a jointed rock mass and they should be considered when designing a support system in a jointed rock mass.

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.17-26
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• 2017

Tunnel excavation in jointed rock mass induces a displacement along tunnel excavation line and its assessment is very important to ensure the stability of tunnel and a demanded space. Tunnel displacement is directly related to the deformation modulus of ground and therefore it is essential to know the value of the parameter. However, most rock masses where tunnels are constructed are generally jointed and it is difficult to find out the deformation modulus of jointed rock mass simply based on an homogeneous isotropic elastic medium because the deformation modulus is highly affected by joint condition as well as rock type. Accordingly, this study carried out extensive numerical parametric studies to examine the variation of deformation modulus in different joint conditions and rock types under the condition of tunnel excavation. The study results were compared with existing empirical relationships and also shown in the chart of deformation modulus variation in different jointed rock mass conditions.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.97-106
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• 2015

We must precisely investigate the mechanical characters of rock to design rock slope safely and efficiently. But the method of clinometer has some disadvantages. So, we need a new measurement that can replace the method of clinometer. In this study, we analyze the reliability of joint orientation measurements in rock slope using the 3D laser scanner and program Split-FX that is a point cloud data analysis software. We could acquire the 495 pieces joint data through the automatic extraction of features. And we confirmed that there were some errors occurred with ${\pm}4^{\circ}$ of dip and ${\pm}5^{\circ}$ of dip direction. Generally, the method of clinometer has ${\pm}5^{\circ}$ and ${\pm}10^{\circ}$ error ranges of the joint orientation(dip/dip direction) that are the results of the advance research. Therefore, we analyzed the method of 3D laser scanner, and it is found to be efficient, reliable. This method is expected to mend the disadvantages of Clinometer method.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.182-189
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• 2001

Rockmass properties have great influence on blasting performance so that it cannot be overemphasized to analyze rockmass properties and to perform blast design based on them. Up to the present, however blast design is performed either considering only uniaxial compressive strength of intact rock or using RMR classification as a blast ability classification scheme. In this paper Ashby's approach is adopted to evaluate blast index. In addition. rockmass classification for the blast design based on joint survey results and pattern design procedure are added to Ashby's original approach. With this extended approach, blastability can be classified considering joint properties and objectiveness of evaluated blast index can be confirmed. This approach is anticipated to enhance the tunnel blast design by considering joint properties and classifying the rockmass for blast design.

• Explosives and Blasting
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• v.24 no.1
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• pp.21-28
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• 2006

Rock mass classification systems such as RMR and Q system have been widely served as a simple empirical approach for the design of various rock mass structures in the stage of site survey as well as under the construction. For the RQD determination, the boring is partially carried out and what is more, the survey boring is not normally carried out under construction. Therefore RQD is frequently determined by empirical method or indirect method. Since it is difficult to determine the discontinuity characteristics such as RQD, spacing, persistence, filling and so on, it is essential to develop suitable and simple systems without drilled core and a cert 없 n number of representative parameters. One of the primary objectives of the classification systems for a practicing engineer has been to make it simple to use as a preliminary design tool for the structures in rock mass. In the present study, the modifications for both the RMR and GSI system are suggested by authors to introduce new classification system as well as to improve the scope of some of the existing classification systems for a practicing engineer.

• Tunnel and Underground Space
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• v.12 no.1
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• pp.10-18
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• 2002

Rock joint system makes a heavy effect on the behavior of rock structures. The definition of a 3D rock joint system is very important in 2D or 3D numerical analysis for the prediction of the behavior of a discontinuous rock mass. To enhance the reality of a 3D definition of rock joint system, it is essential to estimate the unbiased statistics of basic geometric attributes of rock joints. In this study, we have proposed the statistical analysis and derived the related equations for an estimation of statistics of joint size and intensity. Geometry of rock joints in 3 dimensional space can be defined by the aggregate of location, size, orientation and intensity. The dimensional limit of survey method and its data makes 3D geometric attributes probabilistic. In the estimation of statistics of joint size, we have discussed the technique to correct the bias from a dimensional limit and derived the equation of 3D joint intensity by stereological approaches.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.55-66
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• 2014

In this study, a joint survey system was developed to efficiently analyze geometrical characteristics of joint structures in rock mass using photogrammetric technique. The system includes both hardware and software. The hardware consists of a high resolution image camera for photographing image of a surface of rock body, a direction controlling system for adjusting the attitude of camera, and a digital compass for measuring the rotation angle of camera. The software was also developed in order to analyze the orientation, density, mean length of joints revealed on the images of rock surfaces. The software developed in this study was named as JointeXtractor. As applying this system into several field measurements, the orientation, density, mean length of joints could be quantitatively measured through analyzing the images of rock surfaces, in which the case of a difficult-to-access area was especially included for the test of the system.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.294-303
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• 2003

The structural behaviour of rock mass structure, such as tunnel or slope is critically dependent on the various characteristics of discontinuities. Therefore, it is important to survey and analyze discontinuities correctly for the design and construction of rock mass structure. One inevitable Procedure of discontinuity survey and analysis is joint set identification from a lot of raw directional joint data. The identification procedure is generally done by a graphical method. This type of analysis has some shortcomings such as subjective identification results, inability to use extra information on discontinuity, and so on. In this study, a computer program for joint set identification based on the fuzzy clustering algorithm was implemented and tested using two kinds of joint data. It was confirmed that fuzzy clustering method is effective and valid for joint set identification and estimation of mean direction and degree of clustering of huge joint data through the applications.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.229-239
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• 2013

Elastic modulus in rockmass is an important factor to represent the characteristic of rock deformation and is frequently used to estimate the displacement induced due to tunnel excavation or other activities in rockmass. Nevertheless, the study to estimate the elastic modulus, which considers the rock type and joint characteristics (joint shear strength and joint inclination angle), has been done in less frequency. Accordingly, this study is aimed at estimating of elastic modulus in jointed rockmass. For this purpose, numerical parametric studies have been carried out with a consideration of rock and joint conditions. Tunnel displacement results have been used to estimate the elastic modulus of jointed rockmass using the elastic theory of circular tunnel. From this study, the results would be expected to have a great practical use for estimating the displacement induced due to tunnel excavation or other activities in jointed rockmass.

• Explosives and Blasting
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• v.28 no.2
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• pp.1-16
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• 2010

This study focuses on the phenomenon that the blast damaged zone developed on rock slope surfaces can be affected by joint characteristics rather than by explosive power when the pre-splitting is applied to excavate a jointed rock slope. The characteristics of rock joints on a slope were investigated and categorized them into 4 cases. Also an image processing system has been used for comparing the distribution pattern of rock blocks. From this investigation, it was found that the rock blocks bigger than 2,000 mm occupied 42% in the case of single joint set and it showed the well efficiency of pre-splitting blast. In cases of 2~3 parallel joint sets and 2~3 intersecting joint sets are developed on rock surfaces, the rock blocks in the range of 1,000~2,000 mm occupied 43.6% and 35.8%, respectively, and it showed that the efficiency of pre-splitting was decreased. When more than 3 joint sets are randomly developed, however, the rock blocks in the range of 250~500 mm occupied 35% and there was no block bigger than 1,000 mm. This denotes that the blasting with pre-splitting was not effective. The numerical analysis using PFC2D showed that the blast damaged zone in a rock mass could be directly influenced by the pre-splitting. It is, therefore, required to investigate the discontinuity pattern on rock surfaces in advance, when the pre-splitting method is applied to excavate jointed rock slopes and to apply a flexible blating design with a consideration of the joint characteristics.