• Title/Summary/Keyword: Borehole System

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Construction of Efficient Downhole Seismic Testing System by the Round Robin Test (상호검증시험을 통한 효율적인 다운홀 탄성파 기법 수행 시스템의 구성)

  • Bang, Eun-Seok;Kim, Ki-Seog;Kim, Dong-Soo
    • Journal of the Korean Geotechnical Society
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    • v.23 no.4
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    • pp.133-147
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    • 2007
  • Downhole seismic method is very economic and easy of operation because it uses only one borehole and simple surface source to obtain the shear wave velocity ($V_s$) profile of a site. Even though it is widely used by the site investigation companies, universities and institutes, however, the $V_s$ profile determined by downhole seismic method has often low reliability due to employment of wrong combinations of field losing equipment and interpretation method and deficiency of experience. Round robin test was performed and testing equipment and procedure were compared. Adequate downhole seismic testing equipment was constructed based on the comparison and verification study of the round robin test. The data acquisition and software interpretation were also developed for automation and quick test in field. Finally, the effectiveness and applicability were verified through the field test by using the constructed testing system.

Georadar System Using Network-Analyzer (네트웍 분석기를 이용한 레이다탐사 시스템의 구현)

  • Cho Seong-Jun;Kim Jung-Ho;Lee Seoung Kon;Son Jeong-Sul;Chung Seung-Hwan
    • Geophysics and Geophysical Exploration
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    • v.5 no.4
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    • pp.272-279
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    • 2002
  • During field survey of ground penetrating radar or borehole radar, we often encounter some problems which could be solved easily by modifying structure of the system such as antenna length, shape or array. In addition, it is necessary that the user could easily modify configuration of the radar system na test various array of antennas in order to verify and confirm numerical modeling results concerning radar antennas. We have developed network-analyzer-based, stepped-frequency georadar system. This system had been comprised with coaxial cable to confirm possibility of the system, then we have upgraded the system to use optical cable that is composed of optical/electric transducers, electric/optical transducers, amp, pre-amp and antennas. The software for the aquisition of data has been developed to control the system automatically using PC with GPIB communication and to display the obtained data graphically. We have tested the system in field survey na the results have been compared with those of RAMAC/GPR system.

A Performance Prediction of a Vertical-type Geothermal Heat Exchanger by CFD Analysis (CFD 해석에 의한 수직형 지열교환기의 성능예측)

  • Woo, Sang-Woo;Hwang, Kwang-Il;Kim, Jong-Hun;Shin, Seung-Ho
    • Journal of the Korean Solar Energy Society
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    • v.27 no.3
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    • pp.117-125
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    • 2007
  • This study proposes a CFD(Computational Fluid Dynamics) analysis as a method of verification of the designed-data and a supplement of the insufficient experiences in geothermal system, which shows a rapid growth among the renewable energies. The followings are the results. FLUENT 6.2.12 is used as a CFD tool on this study, with the equations of continuity, motion, energy for unsteady flow through pipes and k-epsilon turbulent model. S-type model which has one borehole with diameter 12m by depth 206m and T-type model which has 3 boreholes with $12m{\times}20m{\times}206m$ are proposed, and also the boundary conditions are described. The temperature differences between temperatures by CFD analysis and by on-site measurement are less than 1.5%, this shows a high reliability of CFD analysis process which this study proposes. After 11 days simulation operated 12 hours interval On/Off mode, it is clearly predicted that the outlet temperatures of geothermal pipes are increased by $1.2^{\circ}C$, and $2.2^{\circ}C$ after 4 months. And the outlet temperatures of geothermal pipes increased with increase of the mass flow rates through the pipes. T-type model shows that the 4m distance between boreholes are reasonable because the temperatures at 2m and 6m from boreholes are nearly same.

Seismic Refraction Analysis to Estimate the Depth to the Bedrock: Case Study (기반암 깊이 도출을 위한 굴절법 탄성파 자료 분석: 사례연구)

  • Lee, Doo-Sung
    • Geophysics and Geophysical Exploration
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    • v.8 no.4
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    • pp.237-242
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    • 2005
  • A seismic refraction study in estimation of depth to the bedrock demonstrates that 1) the average velocity in the medium is about 250 m/s in the surface layer (< 4 m), 2,500 m/s in the weathered formation, and greater than 3,000 m/s in the bedrock, 2) the depth to the deepest reflector assumed to be the bedrock is about 17 m; however, according to the cores collected in a borehole in study area, the bedrock (granite) occurred at depth 25 m, 3) according to the density and velocity logging, at depth 17 m, a measurable velocity and density increase are observed, and 4) the velocity of the weathered formation is relatively high and therefore, the acquisition offsets ($70{\sim}80m$) are turned out not to be long enough to record the refracted signal from the bedrock at depth 25 m as first arrivals.

A Study on the Applicability of Amplification Factor to Estimate Peak Ground Acceleration of Pohang Area (국내 내진설계기준의 지반증폭계수를 활용한 포항지역의 지표면 최대가속도 산출 적절성 검토)

  • Kim, Jongkwan;Han, Jin-Tae;Kwak, Tae-Young
    • Journal of the Korean Geotechnical Society
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    • v.36 no.11
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    • pp.21-33
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    • 2020
  • Ground response analysis has been conducted for each borehole data in Pohang area, using 1D equivalent linear method program, to investigate the applicability of amplification factor to estimate peak ground acceleration. Earthquake motions for ground response analysis were prepared by matching response spectrums for return period of 500, 1000, and 2400 years suggested by seismic design code (MOIS, 2017). Ground survey data were acquired from Geotechnical Information DB System. It has been confirmed that response spectrum obtained from ground response analysis showed good agreement with those from seismic design code irrespective of ground classification. However, PGA (Peak Ground Accelerations) of ground response analysis did not coincide with PGA calculated using amplification factor suggested by seismic design code.

A Case Study on Reinforcement of Ground and Foundation against Subsidence in Abandoned Mining Area (폐광지역 침하방지를 위한 지반 및 구조물기초 보강)

  • Kim, Do-Hyung;Choi, Chang-Rim;Kim, Dong-Hyun;Lee, Du-Hwa;Lee, Baek-Song;Je, Hae-Chan
    • Tunnel and Underground Space
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    • v.17 no.4
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    • pp.255-265
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    • 2007
  • As the mechanism and effect range of subsidence are altered according to the various conditions (the ground condition, the earth pressure, the geometric condition of underground cavity and the structure load), the analysis and prediction of subsidence in abandoned mining area are very difficult. Also, as the geological characteristics and the mining methods are differed in each mines, the application of the pre-existing reinforcements without improvement has a lot of difficulties and limits. In this study, the various underground investigation such as long-depth core drilling, seismic tomography and BIPS (borehole image processing system) were performed, the distribution of underground cavity and coal seam and rock relaxation condition were analyzed. And we predicted the type of subsidence and estimated the subsidence by theories of mining subsidence. With these results, we analyzed the mechanism of subsidence occurrence in the research object area. Finally, we improved existing methods which were applied to the abandoned mining area and also we established the rational reinforcement for the ground and structure foundation against each subsidence cause.

Heat transfer analysis of closed-loop vertical ground heat exchangers using 3-D fluid flow and heat transfer numerical model (3차원 열유체 수치해석을 통한 현장 시공된 수직 밀폐형 지중열교환기의 열전달 거동 평가)

  • Park, Moon-Seo;Lee, Chul-Ho;Min, Sun-Hong;Kang, Shin-Hyung;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.09a
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    • pp.800-807
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    • 2010
  • In this study, a series of numerical analyses has been performed in order to evaluate the performance of a full-scale closed-loop vertical ground heat exchanger constructed in Wonju. The circulation pipe HDPE, borehole and surrounding ground were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the system. Two user-defined functions (UDFs) accounting for the difference in the temperatures of the circulating inflow and outflow water and the change of the surrounding ground temperature with depth were adopted in the FLUENT model. The thermal properties of materials estimated in laboratory were used in the numerical analyses to compare the thermal efficiency of the cement grout with that of the bentonite grout used in the construction. The results of the simulation provide a verification of the in situ thermal response test data. The numerical model with the ground thermal conductivity of 4W/mK yielded the simulation result closer to the in-situ thermal response test than with the ground thermal conductivity of 3W/mK. From the results of the numerical analyses, the effective thermal conductivities of the cement and bentonite grouts were obtained to be 3.32W/mK and 2.99 W/mK, respectively.

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Correlation between the Distribution of Discontinuities and Groundwater Flow in Fractured Rock (온도검층과 수압시험을 통한 파쇄암반의 단열분포와 지하수 흐름 상관성 고찰)

  • Park, Seunghyuk;Chung, Il-Moon
    • The Journal of Engineering Geology
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    • v.26 no.4
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    • pp.505-513
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    • 2016
  • The qualitative distribution of a fractured aquifer was characterized by electrical resistivity surveying as a part of basic groundwater investigation in Jangseong. The results were then used to choose sites for observation wells. The locations and distributions of permeable discontinuities were studied by analyses of temperature logs, a borehole image-processing system (BIPS), and hydraulic pressure testing using a double packer. The pressure test showed that the size of the discontinuities correlated with the Lugeon value and the results of the temperature log. The results show that temperature measurement is an effective method to identify permeable discontinuities, with the temperature difference correlating with the size of the aperture of the discontinuity.

Time-series Analysis of Precision the Domestic Boring Investigation Data (국내 시추조사 자료 정밀도 시계열 분석)

  • Jang, Yonggu;Kim, Youngsun;Chae, Deokho;Cho, Wanjei
    • Journal of the Korean GEO-environmental Society
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    • v.16 no.3
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    • pp.15-21
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    • 2015
  • Since the introduction of 'the rule for computerizing subsoil investigation results and its application' in 2007, the DB construction of the national geotechnical information by Ministry of Land, Transport and Maritime Affairs (MOLTMA) has been performed. According to the Integrated DB Center of National Geotechnical Information, there have been 180 thousands borehole information stored in the system. In this study, the time-series analyses of precision on the most used information, the depth of stratum and ground water level, were performed to evaluate the effect of the initiation of the rule established in 2007. The precisions were evaluated based on the statistical analyses using kurtosis and normal distribution. Based on the results, the increase of precision after 2007 and the affirmative effects of the rule established in 2007 are confirmed. Furthermore, the precision of the regional information can be achieved with the precision analyses on the information from various areas.

Estimation of the Effective Hydraulic Conductivity in the Granite Area as an Equivalent Continuum Medium (등연속체매질로서의 화강암지역의 유효수리전도도 산출)

  • 김경수;김천수;배대석
    • The Journal of Engineering Geology
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    • v.12 no.3
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    • pp.319-332
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    • 2002
  • This study is focused on the characterization of an effective hydraulic conductivity in each hydrogeologic unit assumed as an equivalent continuum medium in the granitic area. Four boreholes of 3" diameter were installed and a Multi-packer system was facilitated in the selected borehole. Various in-situ tests including the fracture logging, constant injection and fall-off tests, slug and pulse tests were carried out. A hydrogeologic unit was defined into the upper and lower zones based on the variation of fracture properties and hydraulic conductivities. The difference of the result obtained by the various hydraulic tests and the effective characterization techniques on rock mass permeability are also discussed. The effective hydraulic conductivity of the upper unit was measured by two times(5.27E-10 m/s~7.57E-10 m/s) that of the lower unit(2.45E-10 m/s~6.81E-10 m/s)through the constant injection and fall-off tests.