• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.261-275
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• 2020

When excavating a small cross-section tunnel in a fault fracture zone using the shield TBM method, there is a high possibility of excessive convergence and collapse. Appropriate ground reinforcement is required to minimize construction cost loss and trouble due to a fault fracture zone. In this study, the optimal reinforcement area was suggested and the surrounding ground behavior was investigated through numerical analysis using MIDAS GTS NX (Ver. 280). For the parameters, the width of the fault fracture zone, the existence of fault gouge, and the groundwater level and depth of cover were applied. As a result, when there is not fault gouge, the convergence and ground settlement are satisfied the standard when applying ground reinforcement by up to 0.5D. And, due to the high permeability coefficient, it is judged that it is necessary to apply 0.5D reinforcement. There is a fault gouge, it was possible to secure stability when applying ground reinforcement between the entire fault fracture zone from the top of the tunnel to 0.5D. And, because the groundwater discharge occurred within the standard value due to the fault gouge, reinforcement was unnecessary.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.33-44
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• 2019

Clinker layer is a stratum structure distributed in volcanic area such as Jeju Island. The clinker layers were formed in between the repetitive action of eruption and solidification of lava flows. Since the clinker layer contains a large amount of voids accompanied by the lava gas ejection process, there is a possibility of inducing overall stability of the ground due to the low stiffness and strength of the clinker layer. Therefore, in this study, site investigation was carried out at both ends of the 00 bridge where the clinker layers exist. And, based on the ground survey results, the behavior of shallow foundations was analyzed numerically. In addition, the improved shallow foundation behavior in grouting substitution using the chemical injection method of the clinker layer was compared with the shallow foundation behavior in the ground, and the grouting substitution efficiency of each layer was analyzed. As a result, the bearing capacity, the replacement efficiency and elastic settlement were different according to the presence or absence of the sediment layer. This is because the sediment layer has a lower stiffness and density than the clinker layer.

• Journal of Korean Society of Forest Science
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• v.100 no.4
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• pp.639-649
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• 2011

The purpose of this study aimed to analyze factors on motives to tree burial and choice conditions to tree burial site in order to suggest policy direction for the desirable settlement of tree burial. For those purpose, this study performed questionnaire, targeting 522 visitors of funeral hall all around Korea. As the result, the factors of motives to tree burial were extracted as follows: funeral ceremony progressed along with trees, simplicity, memorial site's easy insurance, environmental friendliness and consideration toward descendants. The factors on choice conditions to tree burial sites were extracted as follows: beauty of natural scenery, emotional mood as a memorial site, convenience, stability and economic feasibility. Based on the results of factor analysis, this study suggested policies related to motives to tree burial as follows: develop various types of tree burial sites, develop a funeral ceremony suitable for tree burial, come into wide use of tree burial as a social welfare service, develop tree burial methods capable of many burials, and improve professionalism to manage tree burial system. In addition, this study proposed related choice conditions to tree burial sites as follows: establish natural forest scenery, convert existing graveyards into tree burial sites, select easily accessible places for tree burial sites, form tree burial sites as places for both rest and memory, and reduce using fee of tree burial site.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.2
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• pp.217-230
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• 2022

The adequate control of TBM face pressure is of vital importance to maintain face stability by preventing face collapse and surface settlement. An EPB shield TBM excavates the ground by applying face pressure with the excavated soil in the pressure chamber. One of the challenges during the EPB shield TBM operation is the control of face pressure due to difficulty in managing the excavated soil. In this study, the face pressure of an EPB shield TBM was predicted using the geological and operational data acquired from a domestic TBM tunnel site. Four machine learning algorithms: KNN (K-Nearest Neighbors), SVM (Support Vector Machine), RF (Random Forest), and XGB (eXtreme Gradient Boosting) were applied to predict the face pressure. The model comparison results showed that the RF model yielded the lowest RMSE (Root Mean Square Error) value of 7.35 kPa. Therefore, the RF model was selected as the optimal machine learning algorithm. In addition, the feature importance of the RF model was analyzed to evaluate appropriately the influence of each feature on the face pressure. The water pressure indicated the highest influence, and the importance of the geological conditions was higher in general than that of the operation features in the considered site.

• Journal of the Korean Geotechnical Society
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• v.39 no.2
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• pp.19-30
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• 2023

Underground structures, such as compacted sand piles applied as soft ground countermeasures, are analyzed for settlement and stability by the composite ground design method. The basic principle of the composite ground design method is the arching effect. The reinforcing effect of the pile is evaluated as the stress-distribution ratio. When applying grouting piles with elastic properties using the ground reinforcement method, the existing stress-distribution ratio was only considered when the pile was installed. This study shows that the method of applying the stress-distribution ratio applied in previous studies should be changed when the ground reinforcement pile is installed at an arbitrary location in the ground without raising it to the ground surface. When high strength jet routing is applied, the stress-distribution ratio (n) to the in-situ ground generally ranges from 30 to 50. However, if the pile is located far from the surface and the depth goes down to the boundary depth of the stress sphere, the stress-distribution effect rapidly decreases, and the stress-distribution ratio converges to 1.5.

• Korean Journal of Culture and Social Issue
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• v.20 no.1
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• pp.19-44
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• 2014

This study was conducted to investigate the types of personality of North Korean female refugees, which were extracted from the T-scores of SPFQ(scales of the Sixteen Personality Factor Questionnaire) and psychological adaptation. For this, The data of 158 North Korean female refugees located in Seoul Yangchun-Gu and Gayang-Gu was analyzed. The results were as follows. Firstly, the ratio of over 65T in ego-strength, self-control, social-boldness, anxiety scales and under 34T in abstractedness and openness to change scales was higher than in other scales. Secondly, there were statistically significant differences in personality characteristics based on the demographic variables especially age and the term of residence in South Korea. Thirdly, three distinct groups were extracted from the K-means cluster analysis. The first group was characterized with emotional-unstability and negative emotionality. And the North Korean female refugees in the second group hesitated to enter into and maintain proper relationships with south korean, while they were unlikely to accept norms and rules in South Korea. The third group, characterized by higher emotional stability, ego-strength, and agreeableness, was met normal range in all the scale of SPFQ. Finally, each three groups were showed statistically significant differences in psychological adaptation scales(self-identity and resilience). We expected that these results contributed to explore the psychological and the political plans for North Korean female refugees' settlement in South Korea.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.93-102
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• 2023

Despite recent modifications to building structural standards emphasizing the seismic stability of building foundations, the current design focus remains solely on vertical support, resulting in insufficient consideration of horizontal loads during earthquakes. In this study, we evaluated the dynamic behavior of inclined tripod micropiles (ITMP), which provide additional seismic resistance against horizontal and vertical loads during earthquakes. A comparison of the dynamic characteristics, such as acceleration, displacement, bending moment, and axial force, of ITMP with a 15° installation angle and normal vertical micropiles with a 0° installation angle was performed using dynamic centrifuge model tests. Results show that under moderate seismic loads, the proposed ITMP exhibited lower acceleration responses than the vertical micropiles. However, when subjected to a long-period strong seismic excitation, such as sine (2 Hz), ITMP showed greater responses than the vertical micropiles in terms of acceleration and settlement. These results indicate that the use of ITMP reduces the amplif ication of short-period (high-f requency) contents compared with the use of vertical micropiles. Therefore, ITMP can be used to enhance seismic performance of structures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.4
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• pp.347-370
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• 2011

Slurry type shield would be very effective for the tunnelling in a sandy ground, when the slurry pressure would be properly adjusted. Low slurry pressure could cause a tunnel face failure or a ground settlement in front of the tunnel face. Thus, the stability of tunnel face could be maintained by applying an excess slurry pressure that is larger than the active earth pressure. However, the slurry pressure should increase properly because an excessively high slurry pressure could cause the slurry flow out or the passive failure of the frontal ground. It is possible to apply the high slurry pressure without passive failure if a horizontal impermeable layer is located in the ground in front of the tunnel face, but its location, size, and effects are not clearly known yet. In this research, two-dimensional model tests were carried out in order to find out the effect of a horizontal impermeable layer for the slurry shield tunnelling in a saturated sandy ground. In tests slurry pressure was increased until the slurry flowed out of the ground surface or the ground fails. Location and dimension of the impermeable layer were varied. As results, the maximum and the excess slurry pressure in sandy ground were linearly proportional to the cover depth. Larger slurry pressure could be applied to increase the stability of the tunnel face when the impermeable layer was located in the ground above the crown in front of the tunnel face. The most effective length of the impermeable grouting layer was 1.0 ~ 1.5D, and the location was 1.0D above the crown level. The safety factor could be suggested as the ratio of the maximum slurry pressure to the active earth pressure at the tunnel face. It could also be suggested that the slurry pressure in the magnitude of 3.5 ~4.0 times larger than the active earth pressure at the initial tunnel face could be applied if the impermeable layer was constructed at the optimal location.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.855-867
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• 2018

When a weak zone exists ahead of tunnel face, the stress in the adjacent area would increase due to the longitudinal arching effect and the stability of the tunnel is affected. Therefore, it is critical to prepare a countermeasure through the investigation of the frontal weakness zone of the excavated face. Although there are several researches to predict the existence of weak zone ahead of tunnel face, such as geophysical exploration, numerical analysis and tunnel support, lack of studies on the relaxation zone depending on the width or distance from the vulnerable area. In this study, the impact of the weak zone on the formation of the relaxation zone was investigated. For this purpose, a series of laboratory test were carried out varying the width of the weak zone and the separation distance between tunnel face and weak zone. In the model test, sand with a water content of 3.8% was used to form a model ground. The model weak zone was constructed with dry sand curtains. The tunnel face was adjusted to allow a sequential excavation of upper and lower half part. load cells were installed on the bottom of the foundation and the tunnel face and measuring instruments for displacement were installed on the surface of the model ground to measure the vertical stress and surface displacements due to tunnel excavation respectively. The test results show that the width of weak zone did not affect the ground settlement while the ground subsidence drastically increased within 0.25D. The vertical stress and horizontal stress increased from 0.5D or less. In addition, the longitudinal arching effect is likely within the 1.0D zone ahead of the tunnel face, which may reduce the vertical stress in the ground following tunneling direction.

• Journal of the Korean Institute of Landscape Architecture
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• v.42 no.5
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• pp.31-40
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• 2014

The importance of green spaces in the city is growing each day. Local governments are taking charge of park development works that are having difficulty in developing and managing urban parks due to high land value as well as a shortage in finances. This is even though an urban park is defined as an urban planning facility and the law provides park area per person. Civil residents, meanwhile, are using not only urban parks provided by law but also other green areas such as rivers, reservoirs, and school playgrounds because they recognize urban green areas by the concept of use. In this study, accordingly, urban green areas were sorted into two types, urban parks, parks provided by law, and other green areas, and the difference in use pattern and use satisfaction by type was analyzed. As a result of analysis, there was no remarkable difference between the two types. According to such results, it was found that it is necessary to include other green areas, such as rivers, reservoirs, school green areas, and apartment green areas in addition to the current park green areas provided by law when park area per person is calculated, and such calculation of urban green areas reflecting local characteristics can reduce local governments' financial burden and improve the effectiveness of future urban park policies. It is judged that such results can become a plan against the cancellation of unexecuted urban facilities. The fact that accessibility factors, such as road satisfaction, access convenience, and convenient movement, are affecting satisfaction with the use of urban parks suggests that it is important to improve urban park accessibilities rather than to quantitatively expand park area in order to improve satisfaction with urban parks. Considering that people travel to urban green areas mostly by walking, it is necessary for access convenience to conduct follow-up studies such as barrier-free and securing walking stability through analysis of routes to urban green areas.