• Journal of the Korean Geosynthetics Society
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• v.23 no.2
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• pp.19-27
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• 2024

Geotechnical structures such as dams, tunnels, and slopes require regular inspection and monitoring to ensure stability. Domestically, drones and accelerometers have become common tools for inspecting and monitoring various structures. However, drones have difficulty identifying internal changes in structures and the subsurface, and accelerometers generally serve for seismic design or strain measurement purposes. Therefore, this paper proposes to utilize accelerometers to monitor the internal information of the ground on a real-time or periodic basis. The proposed method utilizes a part of the analysis technique from the SASW test to monitor the stability and state changes of geotechnical structures. Cases where SASW was used to evaluate the safety of geotechnical structures, such as slopes, dams, and tunnels, were reviewed to verify the suitability of the technology. To make the proposed method more practical, the study considered using only the first-step analysis to derive the dispersion curve rather than the second-step analysis to determine the shear wave velocity profile, which requires complex analysis. The proposed technique is expected to enable the continuous monitoring and inspection of geotechnical structures by utilizing accelerometers.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.73-84
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• 2024

Owing to the high strength and abrasive characteristics of cobble-boulders, cutters are easily worn and damaged during shield tunneling, making construction inefficient. In the present work, the stress on the ripper and scraper on the cutterhead was analyzed by the PFC3D-FLAC3D coupling model of shield tunneling to get insight into the performance of the cutterhead for cutting underground cobble and boulders. The numerical calculation results revealed that the increase in trajectory radius leads to a rising stress on the cutters, and the stress on the front cutting surface is greater than that on the back of the cutters. Moreover, the correlation between cutter wear and stress is revealed based on field measurement data. The distribution of the cutter stress is consistent with the cutter wear and breakage characteristics in actual construction, in which more extensive cutter stress is exhibited, extreme cutter wear appears, and more cutter breakage occurs. Finally, the relationship between the cutterhead opening area's layout and cutter wear distribution was investigated, indicating that the cutter wear extent is the most severe in the region where the radial opening ratio dropped sharply.

• Journal of the Korean Geotechnical Society
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• v.40 no.4
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• pp.113-126
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• 2024

Shotcrete lining is an important material for the stability of tunnels in NATM tunnels. However, stressmeters for stress measurements of shotcrete lining are installed in the field without performance verification because of a lack of research on methods, procedures, regulations, and reliability of measurement equipment. To solve this problem, all shotcrete stressmeters currently used in Korea were investigated. For each stressmeter, external inspection and structural and functional inspection were performed to identify defects and problems in devices. For this purpose, a shotcrete stressmeter performance test device capable of load loading in stages was developed and obtained KOLAS certification. Using the device, stressmeter performance tests were conducted. Structural problems of integrated- and cell-type shotcrete stressmeters were identified through concrete mold tests, and improvement plans and performance verification procedures were suggested. The results of this study are expected to contribute to the preparation of regulations for the performance verification of shotcrete stressmeters and the selection of measuring instruments in the field in the future.

• Journal of the Korean Arthroscopy Society
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• v.7 no.2
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• pp.206-214
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• 2003

Purpose : To analysis each clinical results after arthroscopic ACL reconstruction with using variable fixatives which are metallic and bioabsorbable interference screw, and RIGIDfix. Therefore, We reported the clinical reliability and safty of ACL reconstruction using RIGIDfix. Materials and Methods : We evaluated the results of arthroscopic ACL resconstruction with patellar tendon autograft among three groups, of which group 1 is used metal interference screw for 44 patients, group 2 used bioabsorbable interference screw for 47 patients, group 3 used RIGIDfix for 42 patients. We compared the clinical results by physical examination (anterior drawer test, Lachman test and pivot shift test), Lysholm score and KT-2000 arthrometer and compared the radiological results by measurement of tunnel and fixatives position and widening and by MRI findings. We analyzed the results by SAS 8.2 Ducan. Tukey and paired t-test Results : Physical instability was in 5 cases, which group 2 had 4 cases and group 3 had 1 case. Lysholm score improved from 59.8. 64.4, 61 to 90.1, 92.3. 92. KT-2000 arthrometer instability improved from 9.20, 10.2, 9.5 to 1.43. 1.62. 2.00 (p=0.478). Radiologically, all cases had excellent tunnel position and cyst change was observed the 8 cases in the group 2, but, all 20 cases 2nd MRI had signal change of peri-fixatives. But, no correlation of clinical results. Conclusion : No statistical difference of clinical instability was found among three groups. And femoral tunnel changes were much observed in group I, II than III. We considered the RIGIDfix has much advantages because the short operation time, better fixation position and much bone contact surface. But, further long term follow up study was needed.

• Korean Journal of Ecology and Environment
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• v.52 no.2
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• pp.118-125
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• 2019

Swimming performance of fish is an important factor in the survival of fish. Also, swimming performance of fish is used in the form of habitat, or as a condition to consider when creating a fish ladder. However in Korea, researches in swimming performance of Korean freshwater fish were scarce and inadequate in some part, thus fish ladders were installed without considering their swimming performance. Therefore, in this study, we measured swimming performance of 4 Korean freshwater fish species to consider importance of swimming performance test. The fish used in this study were Carassius auratus, Zacco koreanus, Gnathopogon strigatus, Acheilognathus lanceolata intermedia species which was collected during October to November, 2018 at Geum River, and measurement for swimming speed of each fish was done by using $Loligo^{(R)}$ System, swim tunnel respirometer in January to February of 2019. The average value of the burst critical swimming speed ($U_{crit}$) for each species was $0.8{\pm}0.04m\;s^{-1}$ for C. auratus, $0.77{\pm}0.04m\;s^{-1}$ for Z. koreanus, $0.95{\pm}0.04m\;s^{-1}$ for G. strigatus, $0.73{\pm}0.03m\;s^{-1}$ for A. lanceolata intermedia and the average value of prolonged critical swimming speed was $0.54m\;s^{-1}$ for C. auratus, $0.67m\;s^{-1}$ for Z. koreanus, $0.7m\;s^{-1}$ for G. strigatus, $0.54m\;s^{-1}$ for A. lanceolata intermedia. Since the fish used in this experiment were collected from a small part of the water system in Korea and there were only 4 species, they were not enough to represent the species that inhabit the entire Korean water system. It will be necessary to continue evaluating the swimming performance of other freshwater species in Korea.

• Fire Science and Engineering
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• v.30 no.2
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• pp.27-34
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• 2016

This paper studies a fire detection system using an optical fiber linear detector which can minimize damage from a fire by the most adaptable even in poor environmental conditions such as a tunnel or utility-pipe conduit vulnerable to fire. Using a strand of optical fiber, temperature can be displayed in intervals of meters and a fire can be detected remotely from a distance of several kilometers. Thanks to its strengths such as high reliability and long life, it is widely applied in harsh environments in the overseas. Therefore demands are expected to grow greatly in Korea as well. However, all optical signal drive and analysis module except for the optical fiber linear detector, tend to rely on import. Firstly this study deduced the location and the method of processing signals measuring temperature by using the optical fiber linear detector in order to develop a technology for a domestic model of fire detection system. Secondly this study designed and manufactured the optical analysis test module, and then we checked its performance.

• 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.26 no.5
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• pp.384-395
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• 2016

Both the roughness measurement tests and the multi-stage shear tests were carried out on the 110 rock joint samples in order to investigate the influences of rock type, joint roughness and normal stress on the shear behaviour of rock joints. Test samples were composed of quartz porphyry, dacite, granite and gneiss, which were classified into three detailed groups according to their JRC values. Roughness parameters of rock joints were analyzed by roughness measurement tests, and shear characteristics were also investigated by multi-stage shear tests. Both peak shear strength and shear stiffness were increased as both joint roughness and normal stress were increased, whereas dilation angles showed lower values at the lower roughness and higher normal stress conditions. Besides, shear characteristics obtained from all tests of four different rock types with different rock strengths showed irrelevant details, therefore the influences of both joint roughness and normal stress on shear behaviors were found to be more considerable than the strength of intact rock. The results obtained from both multi-stage shear tests and direct shear tests were finally compared, where the dilation angles obtained from multi-stage shear tests were found to be valid only for the first normal stress conditions.

• Korean Journal of Human Ecology
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• v.17 no.4
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• pp.661-677
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• 2008

The purpose of this study is to develop the playground environment model for child care center by analyzing user needs of playground environment. To systemize the playground environment design factors and guidelines, we reviewed the previous research, actual measurement and observation were used as the research methodology. And to recognize the needs of users, the survey and picture survey was conducted to the staffs and children. The scope of survey included child care centers in Seoul and Daejeon, ultimately selecting 12 places in Seoul and 13 places in Daejeon. In terms of the survey period, actual measurement was conducted from June of 2006 to February of 2007, survey and picture survey was conducted from August to September of 2006. For analysis, we used SPSS 10.0 to check the frequency and percentage, as well as to perform cluster analysis. The findings of research can be summarized as below: 1. In playground environment, we observed the area of play ground and ground cover, the independence of play area, play equipment, and the composition of play area. The result of observation showed that while playground area varied widely, ground cover, play equipment, and the composition of play area turned out to be identical, regardless of the playground's area. Therefore, in order to classify various playground environments, we categorized them into 5 types, using the number of children and the area of play ground as a category. Type A had large facilities and small playground area. Type B had small sized facilities and large playground area. Type C had medium sized facilities and small playground area. Type D had medium sized facilities but large playground area. Type E had large sized facilities and large playground area. 2. On the other hand, staffs wanted a tunnel, playhouse, comprehensive play equipment, and a maze to be installed as play facilities, and there were requests for adventure play area and carpenter play area. The picture survey to children showed that they wanted equipments that can provide more thrill, adventure and challenge to them than the ones they see now. Therefore, existing child care center play environments must change from the monotonous and identical environments to the ones that can provide diversities, challenges, and adventures. In the contexts of 5 playground types suggested by this research, type B and D, E where the area of playground were larger than the legally required, should include various play areas and install appropriate play equipments and facilities. Type A and C where the area were small, should provide multipurpose play area to attract the various play behaviors of children.

• Tunnel and Underground Space
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• v.27 no.1
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• pp.26-38
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• 2017

In this study, bedding rock permeability was measured using Berea sandstones with three different beddings. The fracture permeability was also measured using tight sandstone with two different fracture regimes considering in-situ stress conditions. The Berea sandstone with vertical, horizontal and non-bedding was used to analyze evolution of permeability upon in-situ stress conditions. In order to describe applied effective stress around rock in underground, the triaxial pressure cell & hydrostatic pressure cell was designed and permeability experiments were performed with controlled axial and confining pressures. The measurement of permeability was conducted by increasing and decreasing effective stress. The permeability of non-bedding rock sample is the most sensitive to applied stress conditions and fracture permeability of tight sandstone increases with fracture treatment with proppant.