• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.23-33
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• 2012

Recently, landslide disasters caused by severe rain storms and typhoons have been frequently reported. Due to the geomorphologic characteristics of Korea, considerable portion of urban area and infrastructures such as road and railway have been constructed near mountains. These infrastructures may encounter the risk of landslide and debris flow. It is important to evaluate the highly risky locations of landslide and to prepare measures for the protection of landslide in the process of construction planning. In this study, a landslide-risk prediction equation is proposed based on the statistical analysis of 423 landslide data set obtained from field surveys, disaster reports on national road, and digital maps of landslide area. Each dataset includes geomorphologic characteristics, soil properties, rainfall information, forest properties and hazard history. The comparison between the result of proposed equation and actual occurrence of landslide shows 92 percent in the accuracy of classification. Since the input for the equation can be provided within short period and low cost, and the results of equation can be easily incorporated with hazard map, the proposed equation can be effectively utilized in the analysis of landslide-risk for large mountainous area.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.121-129
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• 2019

An Earthquake Early Warning (EEW) system is a technology that alerts people to an incoming earthquake by using P waves that are detected before the arrival of more severe seismic waves. P-wave analysis is therefore an important factor in the production of rapid seismic information as it can be used to quickly estimate the earthquake magnitude and epicenter through the amplitude and predominant period of the observed P-wave. However, when a large-magnitude teleseismic earthquake is observed in a local seismic network, the significantly attenuated P wave phases may be mischaracterized as belonging to a small-magnitude local earthquake in the initial analysis stage. Such a misanalysis may be sent to the public as a false alert, reducing the credibility of the EEW system and potentially causing economic losses for infrastructure and industrial facilities. Therefore, it is necessary to develop methods that reduce misanalysis. In this study, the possibility of seismic misclassifying teleseimic earthquakes as local events was reviewed using the Filter Bank method, which uses the attenuation characteristics of P waves to classify local and outside Korean peninsula (regional and teleseismic) events with filtered waveform depending on frequency and epicenter distance. The data used in our analysis were analyzed for maximum P_v values using 463 events with local magnitudes (2 < M_L ≦ 3), 44 (3 < M_L ≦ 4), 4 (4 < M_L ≦ 5), 3 (M_L > 5), and 89 outside Korean peninsula earthquakes recorded by the KMA seismic network. The results show that local and telesesimic earthquakes can be classified more accurately when combination of filtering bands of No. 3 (6-12 Hz) and No. 6 (0.75-1.5 Hz) is applied.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.4
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• pp.277-286
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• 2002

Most of the problems in dealing with the tunnel construction are the uncertainties and complexities of the stress conditions and rock strengths in ahead of the tunnel excavation. The limitations on the investigation technology, inaccessibility of borehole test in mountain area and public hatred also restrict our knowledge on the geologic conditions on the mountainous tunneling area. Nevertheless an extensive and superior geophysical exploration data is possibly acquired deep within the mountain area, with up to the tunnel locations in the case of alternative design or turn-key base projects. An appealing claim in the use of artificial neural networks (ANN) is that they give a more trustworthy results on our data based on identifying relevant input variables such as a little geotechnical information and biological learning principles. In this study, error back-propagation algorithm that is one of the teaching techniques of ANN is applied to presupposition on Rock Mass Ratings (RMR) for unknown tunnel area. In order to verify the applicability of this model, a 4km railway tunnel's field data are verified and used as input parameters for the prediction of RMR, with the learned pattern by error back propagation logics. ANN is one of basic methods in solving the geotechnical uncertainties and helpful in solving the problems with data consistency, but needs some modification on the technical problems and we hope our study to be developed in the future design work.

• Journal of the Korean Geotechnical Society
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• v.31 no.5
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• pp.23-33
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• 2015

In the present study, a ground heat exchanger was installed for each heat source in the system at the site to evaluate ground heat conductivity, constructability, and economic feasibility; the factors considered in the study included ground heat, groundwater, fillers (such as bentonite and pea pebbles) and the shape of the heat exchange pipe (e.g., U and D-U). The aim was to determine the ground heat exchanger appropriate for the geothermal system in the 3rd-phase construction of Incheon International Airport. A comparative cost analysis of the initial costs based on the above information showed that although the initial costs of the regular vertical closed loop-II and modified vertical closed loop were lower than those of the regular vertical closed loop-I, they could not be expected to deliver high economic efficiency from the viewpoint of constructability (filler injection, heat exchange pipe insertion). The initial costs proved to be higher in the case of Geohil.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.145-155
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• 2000

Orientation data of discontinuities are of paramount importance for rock slope stability studies because they control the possibility of unstable conditions or excessive deformation. Most orientation data are collected by using linear sampling techniques, such as borehole fracture mapping and the detailed scanline method (outcrop mapping). However, these data, acquired by the above linear sampling techniques, are subjected to bias, owing to the orientation of the sampling line. Even though a weighting factor is applied to orientation data in order to reduce this bias, the bias will not be significantly reduced when certain sampling orientations are involved. That is, if the linear sampling orientation nearly parallels the discontinuity orientation, most discontinuities orientation data which are parallel to sampling line will be excluded from the survey result. This phenomenon can cause serious misinterpretation of discontinuity orientation data because critical information is omitted. In the case study, orientation data collected by using the borehole fracture mapping method (vertical scanline) were compared to those based on orientation data from the detailed scanline method (horizontal scanline). Differences in results for the two procedures revealed a concern that a representative orientation of discontinuities was not accomplished. Equal-area, polar stereo nets were used to determine the distribution of dip angles and to compare the data distribution fur the borehole method versus those for the scanline method.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.39-47
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• 2003

Rockbursts are mainly caused by a sudden release or the stored strain energy in the rock mass. They have been the major hazard in deep hard rock mines but rarely occur in tunnels. Due to the short history and limited information on rockbursts, the topic has rarely been studied in Korea. Some cases of rockbursts, however, have been reported during construction of a mountain tunnel for waterway. This study focuses on analyzing data on rockbursts obtained from a TBM (Tunnel Boring Machine) tunnel and suggests methods for a comprehensive understanding on rockbursts. From the analysis of the field data of rockbursts, it was found that most rockbursts mainly occurred at the section between the tunnel face and the TBM operating room, and the rock bursting phenomena lasted up to 20 days after excavation in certain areas. The data also show that the bursting spots are located all around the tunnel surface including the face, the wall, and the roof, The maximum size of bursting spots is usually less than 100cm. This study also suggests new scale systems of brittleness and uniaxial compressive strength to evaluate the possible tendency for a rockburst. These systems are scaled based on the scale system of strain energy density. In addition, with these scale systems, this research shows that there are potentially higher tendencies for rockbursts in this specific tunnel. Moreover this research suggests that properties of rock and rock mass, RMR (Rock Mass Rating) value, tunneling method, excavating speed, and depth of tunnel have a strong correlation with rockbursts.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.33-42
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• 2002

Ground reaction curve is a very important information for evaluating the side wall displacements and installation time of the tunnle support. The ground reaction curve can be estimated by analytical closed form solutions derived on the supposition of circular section and isotropic stress condition. The conditions of stress field and tunnel configurations, however, are quite different in practice. Therefore, it is necessary to investigate the effects of stress anisotropy and tunnel configurations in order to use simply in practical design. This paper describes a study of influence factors in the ground reaction curve. In order to evaluate the applicability of analytical closed form solution in practical design, two sets of parametric studies were carried out by numerical analysis in elastic tunnel behaviour: one set of studies investigated the influence of the K and the other set investigated the influence of the tunnel configurations such as circular and horse-shoe shape. In the studies, K value varies between 0.5 and 3.0, initial ground vertical stress varies between 5～30MPa far each K values. The results indicated that the self-supportability of ground is larger in the ground having lower K value. However, it is suggested that the applicability of closed form solution may not be adequate to determine directly the installation time of the support and self-supportability of ground. It is necessary to consider stress anisotropy and tunnel configurations.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.235-246
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• 2003

Since the study of Lee et al.(1994) there have been some case studies on the set-up effect of driven piles in Korea country. However, comprehensive examination on the analyses of the set-up effect with various testing data has not been carried out. In particular, the analysis of the influence of soil type and pile shape on the set-up effect has not been reported. It is necessary to analyse the test results of production piles in order to apply the set-up effect of driven piles for the field engineering. In this study some test piling and analyses were performed to give basic information to the piling design as well as the research on the set-up effect in sandy soils. The analyses on the set-up effect were performed with the monitoring data obtained from the high-strain dynamic loading tests. It was shown that the set-up effect of driven piles was not only affected by soil type but also by soil formation history It turned out that the set-up effect in sandy soils was considerable one that should not be ignored in the field, and that the bearing capacity increase of pile is mainly caused by the increase of shaft resistance. It was shown that the set-up effect of closed pile was larger than that of opened pile in clayey soils, while the set-up effect of opened pile was larger than that of closed pile in sandy soils.

• Journal of the Korean Geotechnical Society
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• v.31 no.10
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• pp.37-47
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• 2015

Recently, the quality of drilled shafts concrete has been improved significantly due to the improved concrete performance, upgraded concrete materials, and better management of on-site constructions. Despite the development, current conventional quality management on concrete constructions is still used without any criticism. In this study, compressive strength test results of more than 200 concrete specimens after 7 and 28 days of curing were collected from one site at Songdo area of Incheon. The concrete specimens were prepared from the concrete with aggregate maximum dimensions of 25 mm, target compressive strength of 40 MPa, and slump of 180 mm. Influential factors including concrete temperature, air temperature, amount of slump, amount of air, amount of salinity on concrete specimen were also examined. The database was established from collected information and statistical analyses were performed. Analyzed results confirm that "the difference between concrete temperature and air temperature" has the largest impact on the compressive strengths of specimens at the durations of 7 and 28 days.

• The Journal of Engineering Geology
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• v.5 no.1
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• pp.1-20
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• 1995

A train overturn accident occurred on March 1993 in the Gupo area, northern part of Pusan, unfortunately had taken a heavy toll of lives and caused a great loss of property as well. The reasons for the subsidence of the basement under the railroads, which presumed to be the main cause of the accident, have been investigated from many different angles, including conventional geotechnical investigation methods. The deduced nuin reasons of the subsidence were: 1. blasting for tunnel excavation (NATM) at about 39 meter under the railroads, and 2. unexpected change of bedrock conditions along the direction of tunnel. But this accident was derived nrranlv from the lack of geological and geotechnical information under railroad area because it was impossible to drill beneath the railroads. This paper introduces a new geophysical survey techniqueseisrnic geotomography, and shows some results of the method applying to investigate the underground structure of the accident area. This method not only overcomes the unfavourable environment which many conventional investigation methods cannot face, but produces an image of underground structure with high resolution. Furthermore, the outputs from geotomogaphic analysis could provide very valuable in-situ basic parameters (like seismic velocities, elastic moduli, etc.) which is essential to the design and construction.