• The Journal of Engineering Geology
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• v.23 no.3
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• pp.201-216
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• 2013

Ground penetrating radar (GPR) surveys were conducted in a sand tank model in a laboratory and at an alluvial field site to detect the groundwater table and to investigate the influence of saturation on GPR response in the unsaturated zone. In the sand tank model, the groundwater table and saturation in the sand layer were altered by injecting water, which was then drained by a valve inserted into the bottom of the tank. GPR vertical reflection profile (VRP) data were obtained in the sand tank model for rising and lowering of the groundwater table to estimate the groundwater table and saturation. Results of the lab-scale model provide information on the sensitivity of GPR signals to changes in the water content and in the groundwater table. GPR wave velocities in the vadose zone are controlled mainly by variations in water content (increased travel time is interpreted as an increase in saturation). At the field site, VRP data were collected to a depth of 220 m to estimate the groundwater table at an alluvial site near the Nakdong river at Iryong-ri, Haman-gun, South Korea. Results of the field survey indicate that under saturated conditions, the first reflector of the GPR is indicative of the capillary fringe and not the actual groundwater table. To measure the groundwater table more accurately, we performed a GPR survey using the common mid-point (CMP) method in the vicinity of well-3, and sunk a well to check the groundwater table. The resultant CMP data revealed reflective events from the capillary fringe and groundwater table showing hyperbolic patterns. The normal moveout correction was applied to evaluate the velocity of the GPR, which improved the accuracy of saturation and groundwater table information at depth. The GPR results show that the saturation information, including the groundwater table, is useful in assessing the hydrogeologic properties of the vadose zone in the field.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.149-149
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• 2011

청정 에너지원으로 높은 잠재력을 가지고 있는 가스하이드레이트는 상업적 기술개발이 미확보된 상태임에도, 우리나라에서 부존이 직접적으로 확인되었기 때문에 에너지원으로서 그 중요성이 부각되고 있다. 현재 전세계적으로 가스하이드레이트 개발 및 생산에 관한 연구가 활발히 진행되고 있으며 이에 대한 기초자료로서 가스하이드레이트가 함유된 퇴적층의 물성자료가 필요하다. 이에 따라 본 연구에서는 입도 분포별 총 5가지의 미고결 시료를 대상으로 투과도, p파속도, 전기비저항 측정을 수행하였다. 연구에 사용된 미고결 시료는 Hama#5($774{\mu}m$), #6($485{\mu}m$), #7($258{\mu}m$), #8($106{\mu}m$) 4가지와 Hama#6과 Hama#7을 1:1($371{\mu}m$)로 혼합하여 사용하였다. 실험에 사용된 장비는 가스하이드레이트를 인공적으로 생성시키기 위해 퇴적층을 모사할 수 있는 고압셀과 자료획득장비, 유체 주입장비, 온도 유지장비이다. 또한 투과도 측정에는 차압계, 전기비저항 측정에 RLC meter, p파속도 측정에 음파 송수신장비를 사용하여 각각의 물성을 측정하였다. 실험과정을 단계별로 요약하면 먼저 시료를 고압셀에 충진한 뒤 주입된 물의 양으로부터 공극률을 측정하고, 절대 투수계수를 측정하였다. 그 후, 메탄가스를 주입하여 퇴적층 내 수포화도(water saturation)를 잔류상태(irreducible saturation)로 유지시키고 메탄가스를 추가적으로 주입하여 원하는 압력까지 가압한 뒤 온도를 $1^{\circ}C$로 낮추었다. 가스하이드레이트의 생성은 급격한 압력강하로부터 알 수 있다. 최종적으로 가스하이트레이트가 함유된 퇴적층의 상대 투수계수를 측정하기 위해 메탄가스를 주입하였고 각각의 측정장비를 통해 전기비저항 및 p파 속도를 측정하였다.$V_g$, $V_h$, $V_w$, $V_ss$는 각각 가스의 부피, 하이드레이트의 부피, 물의 부피, 모래의 부피이다. 또한 수포화도, $S_w=\frac{V_w}{V_v}$이며 하이드레이트 포화도, $S_h=\frac{V_w}{V_v}$, 가스 포화도, $S_g=\frac{V_g}{V_v}$로 정의된다. 본 실험의 결과 투과도는 가스의 부피비, $\frac{V_g}{V}=nS_g$에 민감한 반응을 보였으며, 비저항은 공극수의 부피비, $\frac{V_w}{V}=nS_w$에 민감한 반응을 보였다. 또한 p파 속도는 고체의 부피비, $\frac{V_s+V_h}{V}=n(1-S_h)$에 민감한 반응을 보였다. 이러한 실험의 결과는 가스하이드레이트 개발, 생산 연구에 있어 기초 물성자료로 활용되는데 도움을 줄 것이다.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.6
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• pp.743-752
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• 2009

One of the major problems associated with operation of domestic sewer lines involves hydraulic problems such as insufficient conveyance capacity, exceeding maximum velocity, and deficiency of minimum velocity. It has also been pointed out that influent concentration lower than design concentration of pollutants, which is mainly caused by unidentified inflow and infiltration, degrades the operational efficiency of many sewage treatment plants (STPs). A computer-added analysis method supporting a coupled simulation of sewage quality and quantity is essentially required to evaluate the status of existing STPs and to improve their efficiency by a proper sewer rehabilitation work. In this study, dynamic water quality simulations were conducted using MOUSE TRAP to investigate the principal parameters that governs the changes of BOD, ${NH_4}^+$, and ${PO_4}^{3-}$3- concentrations within the sewer networks based on data acquired through on-site and laboratory measurements. The BOD, ${NH_4}^+$ and ${PO_4}^{3-}$3- concentrations estimated by MOUSE TRAP was lower than theoretical pollution loads because of sedimentation and decomposition in the sewer. The results revealed that sedimentation is a most important factor than other biological reactions in decreasing pollutant load in the sewers of C-city. The sensitivity analysis of parameters pertaining to water quality changes indicated that the effect of the BOD decay rate, the initial DO concentration, the half-saturation coefficient of dissolved BOD, and the initial sediment depth is marginal. However, the influence of settling rate and temperature is relatively high because sedimentation and precipitation, rather than biological degradation, are dominant processes that affect water quality in the study sewer systems.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.9 no.1
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• pp.47-53
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• 1995

In this paper, the characteristics of breakdown voltage($\textrm{V}_{Brms}$) -temperature(T) for air insulated power installation in flowing air with variation of T(30[$^{\circ}C$] -180[$^{\circ}C$]) are presented. To study these subjects, needle-to-needle gap in the circular pipe(inner diameter 5[cm]) are used. Also, theories of gas discharge and hydrodynamics in pipe were used to analysis for the characteristics. The $\textrm{V}_{Brms}$ is proportional to flow velocity. At high velocity, $\textrm{V}_{Brms}$ is described the saturation. At high T(180[$^{\circ}C$]), $\textrm{V}_{Brms}$ is about 4.7(kV] lower than low T(30[$^{\circ}C$]). The empirical equation obtained from this study is $\textrm{V}_{Brms}=A\times{Log[Re}+B$. Where A, B : Constant.

• The Journal of Engineering Geology
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• v.24 no.2
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• pp.161-169
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• 2014

We present the results of an experimental physical weathering study that focuses on fresh and slightly weathered gneiss samples from the Wonju area of Korea. The study investigated changes in the physico-mechanical properties of these samples during accelerated laboratory-based weathering, including analyses of microfracture formation. The deteriorated samples used in the study were subjected to 100-150 freeze-thaw cycles, with index properties and microfracture geometries measured between each cycle. Each complete freeze-thaw cycle lasted 24 hours, and consisted of 2 hours of saturation in a vacuum chamber, 8 hours of freezing at $-21^{\circ}C{\pm}1^{\circ}C$, and 14 hours of thawing at room temperature. Specific gravity and seismic velocity values were negatively correlated with the number of freeze-thaw cycles, whereas absorption values tended to increase. The amount of deterioration of the rock samples was dependent on the degree of weathering of the rock prior to the start of the analysis. Absorption, specific gravity, and seismic velocity values can be used to infer the amount of physical weathering experienced by a gneiss in the study area. The sizes and density of microfracture in the rock specimens varied with the number of freeze-thaw cycles. We found that box fractal dimensions can be used to quantify the formation and propagation of microfracture in the samples. In addition, these box fractal dimensions can be used as a weathering index for the mid-and long-term prediction of rock weathering. The present results indicate that accelerated-weathering analysis can provide a detailed overview of the weathering characteristics of deteriorated rocks.

• Journal of Conservation Science
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• v.30 no.4
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• pp.467-480
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• 2014

This study was focused on measurement methods for stone cultural heritages by analyzing Ultrasonic (P-wave) velocity variations according to the water content and anisotropy of rocks. As a result of analyzing of rock properties, the water content and saturation degree were rapidly changed at the beginning of drying and then showed exponential curve which their rates of change gradually decreased. However, P-wave velocity and its rate of change maintained constant values after natural drying of 10 hours. Therefore, the ultrasonic measurement for stone cultural heritages should be performed after natural drying of 10 hours considering the weather and moisture conditions. In addition, the highest values of anisotropy coefficient exhibited in granite and limestone, and indirect method was insensitive to anisotropy compared to direct method. However, all rocks remained anisotropy by indirect method. Accordingly, ultrasonic measurement considering various directions is required. The research results will contribute to customized non-destructive testing and precise diagnosis for lithological characteristics of stone cultural heritage.

• Tunnel and Underground Space
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• v.6 no.4
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• pp.342-347
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• 1996

The changes of electromagnetic wave velocity in rock were monitored to investigate rock behaviors due to the drill & blasting excavations through georadar tomography during the construction of the underground rock laboratory (5 m wide, 6 m high, and 140 m long) at Mabuk-Ri, Goosung-Myun, Yongin-Si, Kyunggi-Do. Two horizontal boreholes spaced 1.4 m apart were drilled parallel to the test tunnel before excavating it, high-resolution crosshole georadar tomography with about 500 MHz electromagnetic waves was performed at pre-excavation phase (May, 1996) and post-excavation phase (August, 1996). The data were acquired with the combination of 34 sources and 44 receivers with space of 0.3 m. Only 11 continuous receivers were selectively utilized with one fixed source. Sampling interval was 0.4 ns and each trace has 512 samples. The first arrival of each trace was picked manually with a picking software. The total number of rays used in inversion amounted to 34x11 and the size of pixel was determined to be 0.3 m. As an inversion technique, SIRT(Simultaneous Iterative Reconstruction Technique) was applied in this study. The velocity of electromagnetic waves at post-excavation phase decreased as large as 15% in comparison with that at pre-excavation phase, which may be attributed to the creation of micro-cracks in rock due to excavations and saturation with groundwater. Small amount of borehole deviation made a critical effect in radar tomography. Totally different tomograms were created after borehole deviation corrections.

• Korean Journal of Ecology and Environment
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• v.40 no.4
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• pp.576-580
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• 2007

Phytoplankton community dynamics were studied from 2004 to 2006 with two and four weeks interval at mid to lower part of the Nakdong River (Waegwan: RK 194, Goryeong: RK 157, Jukpo: RK 112, Namji: RK 75 and Hanam: RK 63: RK: distance from the Estuarine Barrage), South Korea. Annual averages of water temperature was about $16^{\circ}C$, and dissolved oxygen was ranged between 10.0 and 11.5 mg $L^{-1}$ (percent saturation, 106.5 to 112.8%). Diatoms were dominant group with over 60% of phytoplankton abundance in all study sites (Waegwan: 64%, Goryeong: 69%, Jukpo: 73%, Namji: 79%, and Hanam: 83%). However, the occasional dominances of other groups such as green algae and blue-green algae were observed from March to October. Stephanodiscus hantzschii was dominant species and the relative abundances were highat all study sites (48-72%). The ratio of S. hantzschiiltotal phytoplankton abundance were showed a clear increasing tendency toward the estuarine barrage: i.e. 0.31 at Waegwan, 0.39: Goryeong, 0.50: Jukpo, 0.56: Namji, 0.60: Hanam. The results of this study provide the information that the phytoplankton community structure in a regulated river system is basically affected by the physical properties such as water velocity and retention time, resulting in single species dominance by the stagnancy of river flow.

• Geomechanics and Engineering
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• v.23 no.4
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• pp.339-349
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• 2020

This study investigates the feasibility of using the results of the UPV (ultrasonic pulse velocity) test to assess the UCS (unconfined compressive strength) of unsaturated soil. A series of laboratory tests was conducted on samples of unsaturated lateritic soils of northern Taiwan. Specifically, the unconfined compressive test was combined with the pressure plate test to obtain the unconfined compressive strength and its matric suction (s) of the samples. Soil samples were first compacted at the designated water content and subsequently subjected to the wetting process for saturation and the following drying process to its target suction using the apparatus developed by the authors. The correlations among the UCS, s and UPV were studied. The test results show that both the UCS and UPV significantly increased with the matric suction regardless of the initial compaction condition, but neither the UCS nor UPV obviously varied when the matric suction was less than the air-entry value. In addition, the UCS approximately linearly increased with increasing UPV. According to the investigation of the test results, simplified methods to estimate the UCS using the UPV or matric suction were established. Furthermore, an empirical formula of the matric suction calculated from the UPV was proposed. From the comparison between the predicted values and the test results, the MAPE values of UCS were 4.52-9.98% and were less than 10%, and the MAPE value of matric suction was 17.3% and in the range of 10-20%. Thus, the established formulas have good forecasting accuracy and may be applied to the stability analysis of the unsaturated soil slope. However, further study is warranted for validation.

• Fire Science and Engineering
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• v.24 no.1
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• pp.1-7
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• 2010

This paper shows combustion characteristics of fallen leaves of Quercus variabilis and Pinus densiflora according to variation of mass densities. Combustion temperature, mass loss rate, flame height, duration of combustion and velocity of hot gas are measured and analyzed. For the experiment 10cm heighted baskets with varying diameters of 20, 30, 40 and 50cm are used for the combustion and the pilot ignition is carried on the top of the fuel. In case of Pinus densiflora mass loss rate, duration of flame, flame height and combustion time become larger as the mass density and diameter of basket increase, on the other hand Quercus variabilis shows saturation characteristics in mass loss rate and flame height. Velocity of hot gas is proportional to flame height.