• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.41-49
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• 2006

This paper demonstrates the feasibility of using shallow S-wave, high-resolution seismic reflection surveys to characterize geological structure and stratigraphy of basement rocks for civil engineering purposes. S-wave seismic reflections from depths less than 20 m were recorded along the top of steep readout slopes. Seismic reflection data were recorded using a standard CDP acquisition method with a 24-channel seismograph and a sledge-hammer SH-wave source. The data were acquired using a split-spread source-receiver geometry with a 2 m shot-and-receiver interval, and then were processed to enhance S/N ratio of the data, to improve resolvable power of the seismic section, and to get velocity information of the basement rock. The final seismic reflection profiles using the CDP technique has imaged surfaces as shallow as less than 1m and resolved beds as thin as 1m. The migrated reflection sections possess sufficient quality to correlate the prominent reflection events to the bedding planes and faults identified on the readout outcrops. Similar S-wave reflection surveys could also be used to produce the necessary details of a geological structure of shallow bedrocks to pinpoint optimum locations for monitor wells of civil engineering purposes.

• Geophysics and Geophysical Exploration
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• v.26 no.2
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• pp.84-93
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• 2023

The supervised learning-based deep-learning seismic inversion techniques have demonstrated successful performance in synthetic data examples targeting small-scale areas. The supervised learning-based deep-learning seismic inversion uses time-domain wavefields as input and subsurface velocity models as output. Because the time-domain wavefields contain various types of wave information, the data size is considerably large. Therefore, research applying supervised learning-based deep-learning seismic inversion trained with a significant amount of field-scale data has not yet been conducted. In this study, we predict subsurface velocity models using Laplace-domain wavefields as input instead of time-domain wavefields to apply a supervised learning-based deep-learning seismic inversion technique to field-scale data. Using Laplace-domain wavefields instead of time-domain wavefields significantly reduces the size of the input data, thereby accelerating the neural network training, although the resolution of the results is reduced. Additionally, a large grid interval can be used to efficiently predict the velocity model of the field data size, and the results obtained can be used as the initial model for subsequent inversions. The neural network is trained using only synthetic data by generating a massive synthetic velocity model and Laplace-domain wavefields of the same size as the field-scale data. In addition, we adopt a towed-streamer acquisition geometry to simulate a marine seismic survey. Testing the trained network on numerical examples using the test data and a benchmark model yielded appropriate background velocity models.

• Economic and Environmental Geology
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• v.9 no.1
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• pp.1-11
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• 1976

It is believed that geological survey, drilling and geophysical survey which was carried out on Tertiary deposits in Pohang is a valuable but through the studying of many Tertiary sediments in Japan discovered many questions on analysis of final report prepared by National geological survey. The main reason is: 1. The seismic sound velocity which have regulated in the final report prepared by geological survey for Tertiary deposits in Pohang was 1,500-2,000m/sec in spite of oil bearing sediments of same age in Japan are 2,000-3,800m/sec. These may means the requirement of reconsideration of seismic velocity for Tertiary deposits in Pohang and required to have a dipper drilling. 2. Stratigraphically, geophysically, and paleontologically, the Tertiary deposits in Pahang land area is similar with that of Nishiyama-Hunakawa formations of Akita oil field in Japan. Nishiyama-Hunakawa formation is the main oil bearing formation in Japan. 3. Those valcanic rock including andestitic rock and liparitic rock which have extensively distributed over either at land area or at sea bottom, assumed by geological survey as the base of Tertiary sediments. But in case of Japan many oil bearing deposits are in over laid by these kind of volcanic rock. Therefore a possible of same condition with Japan is presumable on Tertiary sediments in Pohang. 4. It is believed that the Tertiary sediments of land area in Pohang is the extension of offshore basin but is wandering that the final report submitted by geologic survey have not remain any word on report of ECAFE discribed so much problematics as followed: A. Although it was assumed that no great thickness exceeding 1,000 meters, or major structures would be encountered in the Tertiary offshore sequence, it was hoped that shallow hydrocarbon deposits might be found, because these sediment are lithologically similar to those of the same age in the producing area of the northwest Honshu region of Japan where hydrocarbon are extracted from depths of only 500 to 600 meters. B. Four possible hydrocarbon trap conditions are represented in the survey area: anticlinal folds, faults, pinch outs, along the igneous basement and lateral facies changes. C. Most of the prime possible reservoir area are beyond the 50 meter water depth mark, except for the structures in Yonil Bay. D. Despite the shallowness of the offshore basin, sufficient trap condition exist in the area to warrant further exploration for hydrocarbon. 5. All of the problems mentioned above have gave us a strong reasons to have us hesitating to make a final conclusion on Tertiary problems in Pohang, before to have a drill to a depth to 3,000 meters or more whatever it is the Tertiary or a Mesozoics below 1,000 meters.

• Geophysics and Geophysical Exploration
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• v.8 no.4
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• pp.243-250
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• 2005

Analysis of high-resolution seismic profiles acquired from the inner shelf off the southern coast of Korea reveals that the inner shelf sequence can be divided into three stratigraphic units formed after the Last Glacial Maximum (LGM). Unit I is characterized by complex seismic facies including semi-transparent, stratified, and hummocky reflections on seismic records. It consists of sandy mud or muddy sand, deposited under estuarine environment during the post-glacial transgression. Unit II acoustically shows semi-transparent or hummocky reflections and consists of sand with gravels and shell debris, produced by shoreface erosion during the transgression. Unit III is characterized by transparent or semi-transparent seismic facies and consists of mud originated from the Nakdong and Seomjin rivers during recent highstand of sea level. Unit III is confined to the inner shelf with an extenal form of stratal wedge.

• Steel and Composite Structures
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• v.37 no.3
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• pp.307-321
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• 2020

The slim-floor solution provides an efficient alternative to the classic slab-over-beam configuration due to architectural and structural benefits. Two deficiencies can be identified in the current state-of-art: (i) the technique is limited to nonseismic applications and (ii) the lack of information on moment-resisting slim-floor beam-to-column joints. In the seismic design of framed structures, continuous beam-to-column joints are required for plastic hinges to form at the ends of the beams. The present paper proposes a slim-floor technical solution capable of expanding the current application of slim-floor joints to seismic-resistant composite construction. The proposed solution relies on a moment-resisting connection with a thick end-plate and large-diameter bolts, which are used to fulfill the required strength and stiffness characteristics of continuous connections, while maintaining a reduced height of the configuration. Considering the proposed novel solution and the variety of parameters that could affect the behavior of the joint, experimental and numerical validations are compulsory. Consequently, the current paper presents the experimental and numerical investigation of two slim-floor beam-to-column joint assemblies. The results are discussed in terms of moment-rotation curves, available rotational capacity and failure modes. The study focuses on developing reliable slim-floor beam joints that are applicable to steel building frame structures located in seismic regions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.247-258
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• 2004

Two 3-dimensional data processing techniques to predict the fractured zone ahead of a tunnel face by the tunnel seismic survey were proposed so that the geometric formation of the fractured zone could be estimated. The first 3-dimensional data processing technique was developed based on the principle of ellipsoid, The input data needed for the 3D migration can be obtained from the 2-dimensional tunnel seismic prediction (TSP) test where the TSP test should be performed in each sidewall of a tunnel. The second 3-dimensional migration technique that was developed based on the concept of wave travel plane was proposed. This technique can be applied when the TSP is operated with sources in one sidewall of a tunnel while the receivers are installed in both sidewalls. New migration technique was applied to an in-situ tunnelling site. The 3-dimensional migration was performed using measured TSP data and its results were compared with the geological investigation results that were monitored during tunnel construction. This comparison revealed that the proposed migration technique could reconstruct the discontinuity planes reasonably well.

• The Korean Journal of Petroleum Geology
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• v.6 no.1_2 s.7
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• pp.1-7
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• 1998

A multichannel seismic profile from the southwestern margin of the Ulleung Basin, East Sea, was analysed in detail to interpret the middle to late Miocene sequence stratigraphic evolution of the area. A regressive package is overlying a transgressive package which, in turn, is underlain by older uplifted and deformed sedimentary layers. A prominent condensed section separates the regressive and transgressive packages. The transgressive package is characterized by onlapping onto the underlying uplifted and deformed strata. The regressive package contains six prograding sequences composed of seismically resolvable lowstand, highstand, and transgressive systems tracts. Most of the depositional sequences comprise lowstand systems tracts consisting of basin-floor fan, slope fan, and prograding complex. Potential reservoirs in the regressive package are turbidite sands in basin-floor fans, channel-fill sands and overbank sand sheets in slope fans, and incised valley-fill sands in the shelf. The shallow marine sands in transgressive packages are another type of reservoir. Detailed sequence stratigraphic analysis, seismic data reprocessing, and 3-D seismic survey are suggested for the successful hydrocarbon exploration in the study area.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.99-104
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• 2009

We propose a waveform inversion method for SH-wave data obtained in a shallow seismic refraction survey, to determine a 2D inhomogeneous S-wave profile of shallow soils. In this method, a 2.5D equation is used to simulate SH-wave propagation in 2D media. The equation is solved with the staggered grid finite-difference approximation to the 4th-order in space and 2nd-order in time, to compute a synthetic wave. The misfit, defined using differences between calculated and observed waveforms, is minimised with a hybrid heuristic search method. We parameterise a 2D subsurface structural model with blocks with different depth boundaries, and S-wave velocities in each block. Numerical experiments were conducted using synthetic SH-wave data with white noise for a model having a blind layer and irregular interfaces. We could reconstruct a structure including a blind layer with reasonable computation time from surface seismic refraction data.

• Earthquakes and Structures
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• v.17 no.4
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• pp.411-424
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• 2019

In this study, a numerical model of a shield tunnel with an assembled segmental lining was built. The seismic response of the segmental lining of the section of the shield tunnel in Line 1 of the Chengdu Metro is analyzed as it passes through the interface of sand-cobble and mudstone layers. To do so, the node-stress seismic-motion input method was used to input the seismic motion measured during the 2008 Wenchuan earthquake, and the joint openings and dislocations associated with the earthquake action were obtained. With reference to the Ethylene-Propylene-Diene Monomer (EPDM) sealing gaskets used in the shield tunnels in the Chengdu Metro, numerical simulation was applied to analyze the contact pressure along the seepage paths and the waterproof property under different joint openings and dislocations. A laboratory test on the elastic sealing gasket was also conducted to study its waterproof property. The test results accord well with the numerical results and the occurrence of water seepage in the section of the shield tunnel in Line 1 of the Chengdu Metro during the 2008 Wenchuan earthquake was verified. These research results demonstrate the deformation of segmental joint under earthquake, also demonstrate the relationship between segmental joint deformation and waterproof property.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.697-703
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• 2008

Excessive water leakage phenomenon happens through damage of nation core zone of about 17,000 storage of water facilities or collapse of dam is worried, is being damaged or enforce dilapidated fill dam core zone's repair reinforcement. Example that use grouting method of construction considering construction and economic performance etc. recently by repair reinforcement way about defect of dam is increased. Permeation grouting method repair & reinforcement of fill dam countermeasure is preferred in nation. Do that is economical to decide these repair reinforcement effect and grouting effect estimation method that do not give damage to dam is effective. Therefore, observing electricity resistivity Survey change of dam since grouting reinforcement using Electric resistivity Survey inquiry of seismic survey method in this research, Wished to verify grouting effect whether is possible as Electric resistivity Survey, and study whether integrity of dam through repair reinforcement defined.