• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.3
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• pp.257-272
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• 2016

It is usually not an easy task to counter-measure on time and appropriately when confronting with troubles in mechanized tunnelling job-sites because of the limitation of available spaces to perform those actions with the existence of disk cutter, cutter head, chamber and other various apparatus in Tunnel Boring Machine (TBM). So, it is important to predict the ground condition ahead of a tunnel face during tunnel excavation. Efforts have been made to utilize geophysical methods such as elastic wave survey, electromagnetic wave survey, electrical resistivity survey, etc for predicting the ground condition ahead of the TBM tunnel face. Each prediction method among these geophysical methods has its own advantage and disadvantage. Therefore, it might be needed to apply several geophysical methods rather than just one to predict the ground condition ahead of the tunnel face in the complex and/or mixed grounds since those methods will compensate among others. The problem is that each prediction method will give us different answer on the predicted ground condition; how to combine different solutions into a most reasonable and representative predicted value might be important. Therefore, in this study, we proposed a methodology how to systematically combine each prediction method utilizing probabilistic analysis as well as analytic hierarchy process. The proposed methods is applied to a virtual job site to confirm the applicability of the model to predict the ground condition ahead of the tunnel face in the mechanized tunnelling.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.3
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• pp.269-282
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• 2008

In general, the effects of steel ribs are not considered in the numerical analysis of tunnel design. However, attempts have been increased recently to consider these effects in the analysis of shallow tunnels in soft ground, based on the fact that the steel ribs embedded in the shotcrete take a role to support some portion of the redistributed load due to excavation. In such analyses, the steel ribs can be considered in four different methods: (1) a conventional method where the steel ribs are not considered, (2) a method using the equivalent composite cross section in which the bending moment of shotcrete is not considered, (3) a method using the equivalent composite cross section in which both the compressive stress and the bending moment for the shotcrete and steel rib are considered, and (4) a method using beam elements for the shotcrete and the steel rib, respectively. These methods are adopted in the numerical analysis using FLAC 2D to investigate stresses of both the shotcrete and the steel rib. The overall results show that the analyses are more practical and economical when the effects of steel rib are considered fer the methods (2), (3), and (4). Since the results of those analyses considering steel rib capacity may be different according to the ground condition, it will be necessary to consider the appropriate method among them in accordance with design conditions.

• Journal of Conservation Science
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• v.34 no.2
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• pp.97-106
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• 2018

The lime-soil mixture on barrier (LSMB) tomb is a representative type of tomb from the Joseon Dynasty. It is an important reference for understanding the society and funeral culture of that time. The LSMB excavated at the Gungri site were classified with manufacturing type. The ultrasonic velocity and rebound hardness method were used to estimate the physical properties of the LSMB. The strength values on the tomb of layered wall were different depend on measuring method. The compressive strengths of the tomb with layered wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 4.0 to 355 (mean 43.6) $kgf/cm^2$ and 18.8 to 538 (mean 245.2) $kgf/cm^2$ ranges. The damage to the tomb with integrated wall during excavation and removal of the corpse could be a reason for the difference in results obtained using ultrasonic velocity method. Compressive strengths of tombs with integrated wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 5.7 to 793 (mean 281.6) $kgf/cm^2$ and 4.5 to 550.5 (mean 172.4) $kgf/cm^2$ values. Physical properties on the tombs of integrated wall had different in compressive strength value but showed similar tendency. Thus, evaluation of the physical properties has shown that measuring ultrasonic velocity and rebound hardness methods are more effective in the LSMB with integrated walls. Further, the strength values obtained through the rebound hardness method are more constant than those obtained through the ultrasonic method due to the small detection area required by the former.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.98-106
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• 2008

When a tunnel is excavated in a rock mass of poor condition, the adjacent zone of excavation surface may be reinforced by adopting the appropriate methods such as grouting and rock bolting. The reinforced effect can be evaluated by use of various numerical approaches, where the reinforcing elements may be expressed as distinct discretizations or smeared into the equivalent material properties. In this study, a simple numerical method, which can be classified as the latter approach, was developed for the elasto-plastic analysis of a circular tunnel. If a circular tunnel in a Mohr-Coulomb rock mass is reinforced to a finite thickness, the reinforced annulus may have different material properties from the in-situ rock mass. In the proposed elasto-plastic method for assessing the reinforcing effect, Lee & Pietruszczak (2007)'s method is applied to both the reinforced annulus and the outer insitu rock mass of the fictitious tunnel, and then two results are combined by enforcing the compatibility condition. The method were verified through comparing the results with the proposed method and the commercial finite difference code FLAC. When taking the variation of deformation modulus and strength parameters in the reinforced zone into account, the distributions of stress and radial displacement were much different from those obtained with the assumption of homogeneous rock mass.

• Journal of the Korean Geosynthetics Society
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• v.22 no.3
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• pp.11-25
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• 2023

In this study, the design and numerical analysis method of the inclined self-supported wall using cement treated soil were studied. In the case of the inclined self-supported wall, the active earth pressure decreased due to the decrease in the coefficient, Ka according to the slope (angle) and the weight decreasing effect, thereby increasing the overall stability. The wall with the slope caused a change in failure mode from overturning to sliding on the excavation side, and the optimal slope was evaluated to be about 10°. Compared to the strength reduction method, the overall stability in numerical analysis results in conservative results in limit equilibrium analysis, so it was found that this method should be attended when designing. As a result of the parameteric study, the stability on bearing capacity and compression failure did not significantly increase above the slope of 10° when the surcharge was small (about 20kPa or less). In the case of cohesion of the backfill, The results similar to numerical analysis were found to consider cohesion. It was evaluated that stability on sliding, oveturning, shear, and tension failure increases in proportion to the thickness of the wall, but there is no significant change in the stability on the bearing capacity and compressive failure regardless of the thickness of the wall above a certain angle (about 10°).

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.249-262
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• 2024

Retaining walls are widely used in the construction of underground structures. This study reviews the stability of the high-strength joint buried pile method at a site in Korea. [Consider giving details of the location.] The method is assessed by considering the amount of ground settlement, as calculated by finite element analysis and measured at the site. Comparison of the measured and numerical results confirmed the method's stability and field applicability. Settlement of 13.42~13.65 mm was calculated for seven cross-sections [The Abstract should be comprehensible without reference to the main text. The labels A-A' to G-G' should not be introduced here without explanation.] using numerical analysis, and the measured settlement reached a maximum of 2.00 mm. The observed differences and variations [Please state what differed/varied.] did not exceed the design expectations in any section. Instruments installed at the back of the excavation area were used to assess the conditions. An underground gradient meter recorded a cumulative horizontal displacement of between -0.40 and 0.60 mm, and an underground water meter recorded slight displacements of between -0.21 and 0.28 m compared with the initial measurements. A surface settlement meter observed very little movement, with a maximum of -2.00 mm compared with the initial measurement, thereby confirming the establishment of a stable state within the management criteria.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.4
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• pp.345-363
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• 2024

Steel pipe reinforced grouting method has been widely used to strengthen the crown of tunnel face and prevent groundwater leakage during tunnel excavation. Various injection procedures without sealing have recently been suggested to enhance efficiency. There are two representative injection methods. One is simultaneous injection in segmented batches, and the other is multiple injection using the external packer. The pros and cons of each method were discussed in terms of construction duration and equipment. However, it has yet to be discussed how the injection procedure affects the grout diffusion range in the ground. This study aims to evaluate the grout diffusion range quantitatively by considering the practical grouting sequences. The grout viscosity was measured by laboratory testing. Then, the numerical modeling was structured using the commercial computational fluid dynamics software. Finally, the grout diffusion range affected by the injection procedure and ground conditions was evaluated by performing the numerical parametric study. The results showed that the injection method highly affected the grout diffusion range, especially for inhomogeneous soil. Consequently, it is anticipated that the proper method of steel pipe reinforced grouting will be suggested.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.221-229
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• 2008

The three dimensional model method is widely applied in resource development for feasibility study, mine design, excavation planning and process management by constructing the database of various data in 3 dimensional space. Most of geophysical surveys for the purpose of engineering and resource development are performed in 2 dimensional line survey due to the restriction of the field situation, technical or economical situation and so on. The acquired geophysical data are used as the input for the 2 dimensional inversion under the 2 dimensional assumption. But the geophysical data are affected by 3 dimensional space. Therefore in order to reduce the error caused by 2 dimensional assumption, the 2 dimensional inversion result must be interpreted considering the additional information such as 3 dimensional topography, geological structure, borehole survey etc. The applicability and usability of 3 dimensional modeling method are studied by reviewing the case study to the geophysical data acquired in field of engineering and resource development.

• Journal of the Korean Geotechnical Society
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• v.31 no.10
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• pp.5-16
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• 2015

Considering the conversion of the Korea Construction Standards to Limit State Design (LSD), we analyzed the resistance bias factor for pullout resistance, as a part of the development of the Load and Resistance Factor Design (LRFD) for soil nailing; very few studies have been conducted on soil nailing. In order to reflect the local characteristics of soil nailing, such as the design and construction level, we collected statistics on pullout tests conducted on slopes and excavation construction sites around the country. In this study a database was built based on the geotechnical properties, soil nailing specifications, and pullout test results. The resistance bias factors are calculated to determine the resistance factor of the pullout resistance for gravity and pressurized grouting method, which are the most commonly used methods in Korea; moreover, we have relatively sufficient data on these methods. We found the resistance bias factors to be 1.144 and 1.325, which are relatively conservative values for predicting the actual ultimate pullout resistance. It showed that our designs are safer than those found in a research case in the United States (NCHRP Report); however, there was an uncertainty, $COV_R$, of 0.27-0.43 in the pullout resistance, which is relatively high. In addition, the pressurized grouting method has a greater margin of safety than the gravity grouting method, and the actual ultimate pullout resistance determined using the pressurized grouting method has low uncertainty.

• Journal of the Korean Geosynthetics Society
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• v.11 no.1
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• pp.11-21
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• 2012

The Rankine(1857)'s earth pressure and the Hong and Yun(1995a)'s earth pressure was applied to analyze the lateral displacement of diaphragm wall applied to the Top-Down construction method using the computer program, which is a common design program for diaphragm wall. The lateral displacement estimated by the computer program was compared with the lateral displacement measured by inclinometer. The Rankine's earth pressure has been widely used to design the diaphragm wall in the analysis of computer program. As the result of comparison, the lateral displacement of diaphragm wall was predicted differently according to the applied earth pressures. The behavior of lateral displacement predicted by the Rankine's earth pressure was different with displacement measured by inclinometer and the lateral displacement at the bottom part was overestimated. However, the lateral displacement predicted by the Hong and Yun's earth pressure is similar to the behavior and maximum value of real displacement. Therefore, the Hong and Yun's earth pressure is more suitable than the Rankine' earth pressure to design the diaphragm walls applied to the Top-Down Construction Method.