• Journal of Conservation Science
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• v.28 no.1
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• pp.39-52
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• 2012

The Usuki Stone Buddha Statues in Oita are consisted of 60 Buddhas which represent of Japan carved on the rock-cliff in the 12 to 14th centuries. The basement rock of the statues is dark gray welded lapilli tuff that containing the Aso-4 pyroclastic rock group. Deterioration maps for the Hoki I and the Furuzono Buddha Statues group show multi-directional fissures on the Cakra, and sheeting-off zone at the margin of uprising water. Deterioration rate of the Hoki I group was calculated fissure about 121 in number, 19% of sheeting-off zone and 51% of biological weathering in surface of area. And the Furuzono group was also evaluated as about 48 of fissures in number, 24% of sheeting-off zone and 41% biological weathering. The slope stability assessment results, the Hoki I developed discontinuous planes has possibility of planar, toppling and wedge failures in all caves. Ultrasonic velocity of the Aizen-myooh (basement rock) ranges from 1,520 to 2,794 (average 2,298m/s). And pedestal of Amita-yeorae which has been replaced by new fresh rock is measured as 3,242 to 4,141 (average 3,813m/s). Therefore, we establish of planing conservation treatment and reinforcement methods to fissure, cavity, sheeting-off zone in the Buddha surface.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.57-64
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• 2004

In order to establish the design method of anchored retention walls in cut slope, the behavior of anchored retention walls and backside ground needs to be investigated and checked in detail. In this study, the behavior of anchored retention walls was investigated by instrumentation installed in cut slope for an apartment construction site stabilized by a row of piles and anchored retention walls. When the anchor was installed at each excavating stages, the horizontal deflection of retention wall decreased, while the horizontal deformation of backside ground increased. The deflection of anchored retention wall decreased as the anchor was prestressed. The prestressed anchor farce has a great effect on the deflection of retention walls, while it has little effect on the deformation of its backside ground. The maximum horizontal deflection of anchored retention walls was developed between $1\%\;and\;4\%$ of excavation depth, which are $2\~8$ times larger than max. horizontal deflection of anchored retention walls including rock layers with backside horizontal ground. Meanwhile, SLOPILE (ver. 3.0) program analyzes the slope stability effects for anchored retention walls. As a result of analysis on slope stability analysis, the lateral earth pressure applied at anchored retention piles could be used as the mean values of empirical lateral pressures using anchored retention wall with horizontal ground at its backside.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.749-760
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• 2017

Recently, the proportion of tunnel structures in roads and railways has increased rapidly. Along with this trend, the rate of occurrence of cracks and dropouts in concrete lining of tunnel structures is increasing. Generally, maintenance of such concrete lining is normalized and managed as the core of maintenance work in tunnel maintenance. However, the maintenance of the tunnel pavement is important in securing driver in the tunnel. In the design of tunnels, the underground condition of the tunnel is designed to be in good rock condition, so there have not been many cases of cracks in the tunnel pavement in the past. Recently, the construction of tunnel structures has been rapidly increased, and the length of the tunnels has become longer.Tunnel pavement installed in these ground conditions is increasing the occurrence of cracks in the pavement due to decrease of bearing capacity of the pavement after a long time. In this study, FWD and GPR were conducted to analyze the types of cracks and the reduction of bearing capacity in the tunnel.

• Tunnel and Underground Space
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• v.26 no.6
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• pp.455-465
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• 2016

The collapse of underground mine development void for mineral resources can cause the subsidence of ground surface. In order to prevent the subsidence of ground, data such as maps or pictures of past mining site is important information for current mine reclamation works. In particular, mine subsidence management was based on mining maps and pictures. The process of the mining area surveys, safety evaluation, and ground reinforcement are normally possible with information such as maps and pictures in past mining. During the Japanese colonial period and 1960's, a lot of mines were developed in Korea indiscriminately. However, mining information at that time is limited to use. In the future, mining information will become even more rare. MIRECO intends to establish a realistic alternative solution. In this study, the basic numerical information of developed mine tunnels in Korea is statistically reviewed, and advanced underground cavity measuring technology was studied. 4,473 mine tunnel opening data of 1,784 abandoned mines in korea were collected and sorted. As a result of the analysis, the average value of small mine tunnel openings in Korea was 1.982 m in height and 1.959 m in width. The mean value of shape factor was analyzed as 0.485. The summary of these numerical mine data will be helpful for understanding and researching Korean abandoned mines. Therefore, the development of measurement technology for abandoned mine cavities and tunnels is expected to facilitate more effective mine subsidence management works in Korea.

• Journal of the Society of Disaster Information
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• v.17 no.3
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• pp.454-464
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• 2021

Purpose: There is a need to construct an evacuation passageway for the 2-Arch tunnel, which has been constructed and is in operation. Therefore, it aims to analyze tunnel and center wall behaviour and stability due to excavation of the center wall. Method: We describe the theoretical background of 2-Arch tunnel and evacuation passageway, and focused on analyzing the behaviour of tunnel and wall using 3-dimensional finite element analysis. Parametric analysis according to rock rating was performed with various ground conditions, and the displacement and stress of the center wall were intensively analyzed. Result: With the center wall excavation, the largest amount of settlement was shown in the center of the opening, and the stress was greatest during the first excavation. In addition, it was shown that stress concentration occurred at the top of both openings, and stability reviews considering the concept of allowable stress showed that it exceeded the allowable stress. Conclusion: Although the displacement of the tunnel has secured stability within the allowable standard, the generated stress is found to exceed the allowable standard, so it is necessary to prevent sudden stress release by applying appropriate reinforcement methods during construction.

• 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 Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.1-14
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• 2010

Until now, the evaluation method of spalling depth using Martin et al. (1999)'s linear regression relations has long been known applicable. However, it is not likely that the proposed equation is applicable to the openings other than circular type and mostly overpredict the spalling depth in comparison with actual spalling cases. Moreover, the evaluation method to estimate the spalling width has not been presented yet; it is essential to evaluate the spalling width in addition to the spalling depth, because the shape of the spalled region influences the choice of suitable rock reinforcement. In this study, linear regression equations, in which normalized spalling depth ($d_f/W_D$) and normalized spalling width ($w_f/W_D$) are functions of three spalling evaluation indices, ${\sigma}_1/{\sigma}_c,\;D_{is}(={\sigma}_{max}/{\sigma}_c)$ and ${\sigma}_{dev}/{\sigma}_{cm}$, are established based on in-situ spalling observations and CWFS simulation results. Confidence intervals of 95% using the statistical inference theory are used in verifying the reliability of linear regression equations. Spalling depth ($d_f$) and spalling width ($w_f$) predicted from the proposed linear regression relations, which take three spalling evaluation indices into account, showed reasonable match with in-situ observations by adopting weighting factors considering the degree of variance of linear regression relations.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.519-533
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• 2023

In this study, the linear cutting tests of pick cutters were carried out on a granitic rock with the average compressive strength over 100 MPa. From the tests, the correlation between the cutter acting force and the temperature measured by infrared thermal imaging camera during rock cutting was analyzed. In every experimental condition, the maximum temperature was measured at the rock surface where the chipping occurred, and the temperature generated in the rock was closely correlated with the cutter acting force. On the other hand, the temperature of a pick cutter increased up to only 36℃ above the ambient temperature, and the correlation with the cutter force was not obvious. This can be attributed to the short cutting distance under laboratory conditions and the high thermal conductivity of the tungsten carbide inserts. However, the relatively high temperature of the tungsten carbide inserts was found to be maintained. Therefore, it is recommended that a reinforcement between the insert and the head of a pick cutter or the quality improvement of silvering brazing in the production of a cutter is necessary to maintain the high cutting performance of a pick cutter.