• Tunnel and Underground Space
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• v.18 no.6
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• pp.418-426
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• 2008

A surface blasting method with a single tree face is currently used in Pasir Coal Mine in Indonesia. The single free face is usually the ground surface. This kind of blasting method is easy to use but inevitably causes enormous ground vibrations, which, in turn, can affect the stability of the slopes comprising the various boundaries of the open pit mine. In this regard, we decided to make a specific blasting guideline for the control of found vibrations to ensure the safety of the pit slopes and waste dumps of the mine. Firstly, we derived a prediction equation for the ground vibration levels that could be occurred during blasting in the pits. Then, we set the allowable levels of ground vibrations for the pit slopes and waste dumps as peak particle velocities of 120mm/s and 60mm/s, respectively. From the prediction equation and allowable levels, safe scaled distances were established for field use. The blast design equations for the pit slopes and waste dumps were $D_s{\geq}5\;and\;D_S{\geq}10$ respectively. We also provide several standard blasting patterns for the hole depths of $3.3{sim}8.8m$.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.248-260
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• 2009

With regard to oversea mineral resources development, recent trend has been changed from a simple capital investment to a direct development of the resources. In relation to the stability of a slope in large open-pit coal mine, groundwater system was investigated and the validity of horizontal drainage hole was evaluated in Pasir coal mine, Indonesia. In this work, various field tests were carried out for a characterization of groundwater system, which included in-situ permeability measurement, tracer test and monitoring of groundwater levels. Especially, the influence of SM river on the characteristics of the groundwater flow system was mainly inspected. For the permeability measurement, Guelph permeameter was employed, and was found that sandstone was more permeable than mudstone and coal seam. From a comparison of lithological structure and the results of groundwater level monitoring, sandstone and thin coal seam with fractures were found to be a main channel for groundwater flow. In the results of tracer tests, the effect of SM river on the groundwater system depends on the geological structure of its base. To identify the effect of horizontal drainage holes, 2-D groundwater modeling was performed. Four different cases were tested, which are different from the length of drainage hole and the existence of pond on top of the slope. To enhance the drainage effect and slope stability, the drainage hole should be drilled to the depth of coal seam layer, which provides a main pathway of groundwater flow and embedded by sandstone. For this purpose, correct identification of surrounding geology should be preceded.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.181-189
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• 2009

This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

• Explosives and Blasting
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• v.23 no.4
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• pp.31-44
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• 2005

In highly stressed conditions, the excavation damage zone induced by stress redistribution and disturbance must be evaluated after tunnel excavation. Therefore, the investigation of stress-induced deformation and fracture in rock is indispensable. In this study, fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by the moving point regression technique as well as acoustic emission measured during uniaxial compression tests. Especially, the modified procedures to determine damage thresholds more systematically were newly proposed, and successfully applied to rock. From experiments, crack initiation and track damage stress levels were estimated to be $33{\~}36\%$ and $84{\~}89\%$ of uniaxial compressive strength respectively, for both of Hwangdeung granite and Yeosan marble. However, the normalized crack closure stress level for Yeosan marble was much higher than for Hwangdeung granite. In addition, the largest proportion of total axial strain in Hwangdeung granite was attributable to elastic deformation and initial microcracking. However, the greatest part of axial deformation in Yeosan marble arose from initial crack closure and unstable cracking. Finally, it was seen that unstable cracking after the crack damage stress level played a key part in the lateral deformation in rocks under uniaxial compression.

• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.28-38
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• 2005

According to the recent development of measurement system utilizing one or a set of boreholes, visualization of the explored underground became to be a major issue. It induced even the introduction of monitoring apparatuses on the borehole wall with multi-function tool, but the usage of these was often limited by where is unfavorable rock condition and a few of engineers can approach. And so, a portable type of borehole camera with only the essential function has been investigated and a few of commercial models about this is recently being applied into the field condition. This paper was based on the monitoring results obtained using a commercial model by Dr. Nakagawa. Discontinuities in rock mass were the topic for the visualization, and it was studied how can visualize their three dimensional distribution and what a numerical formulation is needed and how to understand the visualization result. The numerical formulation was based on the geometric correlation between the dip direction / dip of discontinuous plane and the trend / plunge of borehole, a set of the equation of a plane was induced. As field application of this into two places, it is found that the above visualization methodology will be especially an useful geotechlical tool for analyzing the local distribution of discontinuities.

• Tunnel and Underground Space
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• v.15 no.4 s.57
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• pp.264-274
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• 2005

The optimum blasting pattern to excavate a quarry efficiently and economically can be determined based on the minimum production cost which is generally estimated according to rock fragmentation. Therefore it is a critical problem to predict fragment size distribution of blasted rocks over an entire quarry. By comparing various prediction models, it can be ascertained that the result obtained from Kuz-Ram model relatively coincides with that of field measurements. Kuz-Ram model uses the concept of rock factor to signify conditions of rock mass such as block size, rock jointing, strength and others. For the evaluation of total production cost, it is imperative to estimate 3-D spatial distribution of rock factor for the entire quarry. In this study, a sequential indicator simulation technique is adopted for estimation of spatial distribution of rock factor due to its higher reproducibility of spatial variability and distribution models than Kriging methods. Further, this can reduce the uncertainty of predictor using distribution information of sample data The entire quarry is classified into three types of rock mass and optimum blasting pattern is proposed for each type based on 3-D spatial distribution of rock factor. In addition, plane maps of rock factor distribution for each ground levels is provided to estimate production costs for each process and to make a plan for an optimum blasting pattern.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.270-278
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• 2003

Transparency on the Total System Performance Assessment (TSPA) is the key issue to enhance the public acceptance for a permanent high level radioactive repository. Traditionally, the study on features, events and processes (FEPs) and associated scenarios has been regarded as the starting point to open the communicative discussion on TSPA such as what to evaluate, how to evaluate and how to translate outcomes into more friendly language that many stakeholders can easily understand and react with. However, in most cases, it has been limited to one way communication, because it is difficult for stakeholders outside the performance assessment field to assess the details on the story of the safety assessment, scenario and technical background of it. Fortunately, the advent of the internet era opens up the possibility of two way communication from the beginning of the performance assessment so that every stakeholder can exchange their keen opinions on the safety issues. To achieve it, KAERI develops the systematic approach from the FEPs to Assessment methods flow chart. All information is integrated into the web based program named FEAS (FEp to Assessment through Scenario development) under development in KAERI. In parallel, two independent systems are also under development the web based QA(Quality Assurance) system and the PA(Performance Assessment) input database. It is ideal to integrate the input data base with the QA system so that every data in the system can checked whenever necessary. Throughout the next phase R&D starting from the year 2003, these three systems will be consolidated into one unified system.

• Tunnel and Underground Space
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• v.12 no.1
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• pp.52-69
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• 2002

The WIPP (Waste Isolation Pilot Plant), located 42km east of Carlsbad, New Mexico (NM), in bedded salt 655m below the surface, is a mined repository constructed by the US DOE for the permanent disposal of transuranic (TRU) wastes generated by activities related to defence of the US since 1970. Its historical disposal operation began in March 1999 following receipt of a final permit from the State of NM after a positive certification decision for the WIPP was issued by the EPA in 1998, as the first licensed facility in the US for the deep geologic disposal of radioactive wastes. The CCA (Compliance Certification Application) for the WIPP that the DOE submitted to the EPA in 1966 was supported by an extensive performance assessment (PA) carried out by Sandia National Laboratories (SNL), with so-called 1996 PA. Even though such PA methodologies could be greatly different from the way we consider for HLW disposal in Korea largely due to quite different geologic formations in which repository are likely to be located, a review on lots of works done through the WIPP PA studies could be the most important lessons that we can learn from in view of current situation in Korea where an initial phase of conceptual studies on HLW disposal has been just started. The objective of this art report is an overview of the methodology used in the recent WIPP PA to support the US DOE WIPP CCA and some relevant results completed by SNL.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.304-315
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• 2016

In this study, the current horizontal stress characteristics of the Tertiary rock formations in the Pohang Basin are investigated on the basis of the in-situ rock stress measurements at depths from 75 m to 716 m of the 3 test boreholes in the Doumsan area, Pohang. The deep hydraulic fracturing stress measurement results indicated that the horizontal stress components in the test site appear far lower than the average ones by the linear fit for the data set measured from the other domestic sites. But, borehole scanning revealed clearly that lots of small and large scale borehole failures occurred due to the low strength characteristics of the existing rocks. To obtain more accurate and overall information on the horizontal stress direction, the integrated analysis combining the hydraulic fracturing stress measurement and borehole scanning data set were additionally carried out. The analysis results showed that in the upper sedimentary and the lower volcanic rock formation, the dominant orientations of the current maximum horizontal stress components were appeared in the range of $80^{\circ}{\sim}100^{\circ}$ (N80E~N80W) and $120^{\circ}{\sim}140^{\circ}$ (N60W~N40W), respectively. From this study result it was found that the maximum horizontal stress directions have a tendency to rotate in a clockwise direction as the rock formation changes with depth in the test site.

• Tunnel and Underground Space
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• v.25 no.4
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• pp.341-358
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• 2015

This study analyzes the relationship between parameters of the discontinuity in Discrete Fracture Network model such as fracture intensity, fracture orientation, fracture size, fracture shape etc. In this paper, FracMan code was used to model and analyze 3D DFN. A sensitivity analysis was performed in order to analyze the relationship between linear fracture intensity measure ($P_{10}$) and parameters of the discontinuity in $100m{\times}100m{\times}100m$ model area. As a result the sensitivity analysis showed that key parameters affecting fracture intensity are fracture orientation (Trend / Plunge). Conversion factor($C_{13}$) for $P_{10}$, to calculate volumetric fracture intensity measure ($P_{32}$), is derived in case of vertical well and horizontal well when trend is $10^{\circ}$, $30^{\circ}$, $60^{\circ}$, $90^{\circ}$, $120^{\circ}$, $150^{\circ}$, $180^{\circ}$ (7cases) and plunge is $5^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$, $85^{\circ}$ (7cases). It is expected that this paper can be used effectively for modeling and understanding DFN model.