• Tunnel and Underground Space
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• v.20 no.3
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• pp.145-152
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• 2010

In this study, a survey of structural geology and discontinuities were carried out on the space in a limestone mine where the construction of crushing facilities is in planning. The stability of the site was analyzed by rock mass classifications and numerical analysis. Through these analyses, it could be known that removal of pillars could make the stability problems in the mine and the supports for pillars must be considered.

• Explosives and Blasting
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• v.23 no.2
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• pp.37-44
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• 2005

Recent studies reported that natural block size of rock and joint orientation highly affect on rock fragmentation. In this study, blasting test using high strength cement mortar was carried out to verify this fact. The result of this test indicated that fragmentation is influenced by the joint interval, and at same joint interval condition, fragmentation depends on joint orientation. These results are significantly coincident with field investigations.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.103-111
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• 2004

There are some problems in evaluating the bearing capacity of decomposed granite soils by general equations on account of their inherent compressibility and crushability. In order to investigate this kind of the engineering characteristics on decomposed granite soils in detail, it is necessary to how the micro property of the single particle composing the granite soils, and then the relevance to the macro characteristics of the soils has to be cleared. The reason why the single particle properties are not studied is first the difficulty to find out some regulating parameters, and secondly little understanding of its significance. Furthermore, the water in the decomposed granite soils accelerates the particle crushing. Consequently, increasing of compressibility and decreasing of shear strength would occur. Actually, when the ground settlement is a big issue in the embanked ground using the decomposed granite soils, the sensitive change of compressibility due to the change of water content in the ground becomes conspicuous. In this study, the single particle strength characteristics are studied and microscopic particle shape analyses are performed. In addition the compressibility of the decomposed granite soils and water content effect on the compressibility are analysed based on the test results.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.237-247
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• 2001

In this study, the fracture mechanics model as well as the elastic model was reviewed theoretically and four field case studies were conducted to investigate the feasibility of fracture mechanics model for hydraulic fracturing test. There was a difference between the result by fracture mechanics model and the one by elastic model. And the smaller initial crack length is, the larger the difference is. It is considered that the fracture mechanics model can be applied to the specific case of which the crack length is known. In this study, the rock tensile strength is measured using fracture mechanics model, brazilian test and elastic model. The measured tensile strength by the fracture mechanics model is the largest and the elastic model is the smallest. This result is due to the size effect of the each test. And the tensile strength from the elastic model for hydraulic fracturing test can be used to estimate the in-situ rock tensile strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.125-130
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• 2010

It is necessary to re-establish the code and to control the quality of the recycled aggregate itself for ensuring the useability of the recycled aggregate using waste concrete. Generally, adhering mortar cause of the water absorption ratio increment and strength decreased at the surface of the aggregate of the recycled aggregate using waste concrete, thus removing the adhering mortar could increase the useability of the recycled aggregate in the concrete industry. In this study, as a quality control method of the recycled aggregate using waste concrete, the quality characteristic of the recycled aggregate according to the mixing proportion between the recycled and the natural aggregate is obtained Therefore, a system is established to reuse the recycled aggregate in the construction industry.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.353-362
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• 2004

Prediction of fragmentation in bench blasting is one of the most important factors to establish the production plan. It is widely accepted that fragmentation could be accurately predicted using the Kuz-Ram model in bench blasting. Nevertheless, the model has an ambiguous or subjective aspect in evaluating the model parameters such as joint condition, rock strength, density, burden, explosive strength and spacing. This study proposes a new method to evaluate the parameters of Kuz-Ram model, and the predicted mean fragment sizes using the proposed method are examined by comparing the measured sizes in the field. The results show that the predictions using Kuz-Ram model with the proposed method coincide with field measurements, but Kuz-Ram model does not reflect the in-situ rock condition and hence needs to be improved.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.63-79
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• 2011

In this study relative density tests of bottom ash and standard sand were carried out. And cyclic triaxial tests for samples with the relative density of 40%, 55%, and 70% were carried out on the basis of the test results. Cyclic triaxial tests were also conducted for fines content with 55% relative density. Residual samples were divided into No.40, No.60, No.60, and No.100, and No.200. In order to avoid crashing that can happen when compaction of the sample is initiated, bottom ash was crushed using the a compact mold. In consideration of the crushing characteristics of each residual samples, the fragmentation rate increased up to 30%, which led to the adjustment of fine-grained amount to 10%, 20%, and 30%. Through the repative triaxial test in accordance with the relative density, resistant characteristics of the liquefaction of bottom ash was analyzed. Test results show that, crushing strength of bottom ash was smaller than that of standard sand, resulting in different liquefaction behavior characteristics. And we could find fines content with maximum resistant characteristics of the liquefaction.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.37-43
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• 2015

Ground characteristics is important in tunnel structure utilizing the strength of underground. In the case of the fault fracture zone such as weak soil conditions exists in the tunnel section and groundwater leaching occurs at the same time, it happens to occur to excessive displacement or collapse of tunnel frequently. Fault fracture zone is an important factor that determines the direction of displacement and the collapse of the tunnel under construction. Behavior of fault fracture zone is determined depending on the size and orientation of the surface portion of the tunnel. If the groundwater occurs in the face of tunnel, groundwater causes displacement and collapse. And the collapse characteristics of tunnel is a major factor in determining that the time-dependent behavior. It is difficult to accurately predict groundwater leaching from the fault fracture zone in the numerical analysis method and analyze the interaction behavior of groundwater and fault fracture zone. Therefore numerical analysis method has limitations the analysis of ground water in the ground which the fault fracture zone and groundwater occurs at the same time. It is required to comprehensively predict the behavior of tunnel and case studies of tunnel construction. Thus, the location of fault fracture zone is an important factor that determines the direction of displacement and the collapse of the tunnel. In this study, behavior characteristics of the tunnel according to the location of the fault fracture was analyzed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.2
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• pp.132-139
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• 2015

In this study, the different unit cement content by the ratio of water absorption and water-cement ratio are applied to examine the properties of the concrete used the aggregate recycled by the crushing treatment. According to the experimental results, in the mix of low strength and high water-cement ratio, both of the compressive strength is almost equal in the concrete using the recycled aggregate by the crushing treatment and the concrete using broken stones. It means that the recycled aggregate has the low effect of the amount of bonded mortar. But, in the mix of high strength and low water-cement ratio, the concrete using the recycled aggregate by the crushing treatment has 40% less of the compressive strength than that using broken stones by the effect of the amount of bonded mortar. On the other hand, after 8 weeks, the dry shrinkage of the recycled aggregate with 7% of the ratio of water absorption doubles that of the broken stones with 1% ($-350{\times}10^{-6}$), in other words $-700{\times}10^{-6}$. Thus, the dry shrinkage should be prior to any other conditions in recycling waste concrete for the aggregate for concrete. When the recycled aggregate with 3% of the ratio of water absorption is used, the compressive strength of the rich mix concrete ($450kg/m^3$ of the unit cement content) is equivalent to that of the concrete using broken stones, while in using the recycled aggregate with 7% of the ratio of water absorption, the rich mix concrete has 7% lower compressive strength than the concrete using broken stones. But, the compressive strength of the ordinary mix concrete ($350kg/m^3$ of the unit cement content) is far lower than that using broken stones.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.84-91
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• 2010

We built multi-purpose large triaxial testing system that can test and evaluate various geotechnical design parameters such as shear strength, deformation modulus and stress-strain behaviour for large diameter granular materials, which are the most commonly used construction materials in the railway, road embankments. The details of the built testing system and the results obtained from static triaxial test carried out for gneiss ballast material are discussed within the scope of this paper. Ballast is hardly saturated and is confined at low overburden pressure, since the depth is shallow and the permeability is very high. Herein we ascertained that the confining pressure can effectively be controlled by vacuum. The rational trend could be checked up through triaxial test results such as shear strength, deformation, and particle breakage. And the shear strength envelope could be non-linearly represented with the parent rock strength, confining pressure of the triaxial test and proper parameters.