• Journal of the Korean GEO-environmental Society
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• v.23 no.8
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• pp.29-36
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• 2022

The importance of subsurface information is becoming crucial in urban area due to increase of underground construction. The position of underground facilities should be identified precisely before excavation work. Geophyiscal exporation method such as ground penetration radar (GPR) can be useful to investigate the subsurface facilities. GPR transmits electromagnetic waves to the ground and analyzes the reflected signals to determine the location and depth of subsurface facilities. Unfortunately, the readability of GPR signal is not favorable. To overcome this deficiency and automate the GPR signal processing, deep learning technique has been introduced recently. The accuracy of deep learning model can be improved with abundant training data. The ground is inherently heteorogeneous and the spacially variable ground properties can affact on the GPR signal. However, the effect of ground heterogeneity on the GPR signal has yet to be fully investigated. In this study, ground heterogeneity is simulated based on the fractal theory and GPR simulation is carried out by using gprMax. It is found that as the fractal dimension increases exceed 2.0, the error of fitting parameter reduces significantly. And the range of water content should be less than 0.14 to secure the validity of analysis.

• Journal of the Korean Society of Groundwater Environment
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• v.1 no.2
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• pp.90-99
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• 1994

Heterogeneous hydraulic conductivity in a flow domain is generated under the assumption that it is a random variable with a lognormal, spatially-correlated distribution. The hydraulic head and the conductivity in a groundwater flow system are represented as a stochastic process. The method of Monte Carlo Simulation (MCS) and the finite element method (FEM) are used to determine the statistics of the head and the logconductivity. The second moments of the head and the logconductivity indicate that the cross-covariance of the logconductivity with the head has characteristic distribution patterns depending on the properties of sources, boundary conditions, head gradients, and correlation scales. The negative cross-correlation outlines a weak-response zone where the flow system is weakly responding to a stress change in the flow domain. The stochastic approach has a potential to quantitatively delineate the zone of influence through computations of the cross-covariance distribution.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.698-701
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• 2007

지하수 개발가능량 산정을 위한 함양량의 평가는 수문계의 물리적인 형태나 함수층의 수리성 분석 및 수직인 지질분포를 파악하여 어떤 조건하에서 물이 유입 유출되는가를 파악한 후에만 가능하다. 또한 지하수계의 물리적인 형태를 이해함으로써 조사지역의 지표수계나 지하수계의 양계를 통해서 흐르는 물의 양을 결정짓는 물수지 분석이 수행되어야 한다. 이에 따라 강수량, 증발산량, 지하수 유출량, 지표유출량 그리고 하천유출량 등을 수문학적으로 고려해야만 한다. 본 연구는 지표수-지하수 결합모형을 도입하여 분포형 지하수 함양량의 시공간적인 변동성을 파악하는 데 그 목적이 있다. 이를 위해 지표수-지하수 결합모형인 SWAT-K모형을 미호천 유역에 적용하였으며, 지표수의 총유출량과 지하수위의 공간분포자료를 이용하여 검정과 검증을 수행하였다. 전체유역에 대한 연평균 함양량은 수문총량의 약 19%인 것으로 나타났다. 1999년${\sim}$2004년까지의 소유역별 연간 함양량 결과를 월별로 나타냈으며, HRU(Hydrologic Response Unit)별 함양량의 공간분포를 통해 월별, 계절별 특성을 살펴볼 수 있었다. 소유역 모두 강수가 집중하는 7-9월에 걸쳐 많은 함양이 이루어지며 $1{\sim}3$월에는 상대적으로 함양이 적은 것을 볼 수 있다. 월함양량의 경우 최대 약200mm범위내에서 유역의 토지이용 및 토양특성, 경사등에 따라 매우 비균질하게 분포하는 것을 확인할 수 있었다. 이와같은 함양량의 시공간적 불균일성으로 인해 지하수 관리방안은 소유역별 함양특성을 반영해야 할 것으로 판단된다.의 종분산지수가 일반적인 자연대수층에 비해 9.1배 정도 높다는 것을 의미한다. 이는 시험대수층의 투수성이 매우 높아 염소이온의 용질이송이 매우 빠르게 발생되었기 때문이다. 본 연구에서 추정된 종분산지수를 Gelhar et al.(1992)의 연구 결과와 비교 분석한 결과에서도 시험규모에 비해 매우 높은 수리분산이 발생된 것으로 나타났다. 그리고 염소이온의 확산면적을 추정하기 위해, 수렴흐름 추적자시험에 의한 종분산지수와 시험대수층의 평균선형유속을 이용하여 종분산계수를 구하였다. 현장에서 수행된 양수시험에 의한 평균선형유속 22.44 m/day와 평균 종분산지수 0.4155 m를 적용하여 산정된 종분산계수는 $9.32\;m^2/day$이었다. 따라서, 시험부지 내 충적층에서 일정한 양수율$(2,500\;m^3/day)$로 지하수를 개발할 시에 양수정 주변지역으로 유입되는 염소이온의 확산면적은 1일 $9.32\;m^2$ 정도일 것으로 나타났다.적인 $OH{\cdot}$ 의 생성은 ascorbate가 조직손상에 관여할 가능성을 시사하였다.었다. 정확한 예측치를 얻기 위하여 불균질 조직이 조사야에 포함되는 경우 보정이 요구되며, 골반의 경우 골 조직의 보정이 중요한 요인임을 알 수 있었다. 이를 위하여 불균질 조직에 대한 정확한 정보가 요구되며, 이는 CT 영상을 이용하는 것이 크게 도움이 되리라 생각된다.전시 슬러지층과 상등액의 온도차를 측정하여 대사열량의 발생량을 측정하고 슬러지의 활성을 측정할 수 있는 방법을 개발하였다.enin과 Rhaponticin

• Tunnel and Underground Space
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• v.27 no.5
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• pp.333-342
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• 2017

In this study, the heterogeneity of internal structure of various igneous rocks acquired in Korea was quantified and correlated with the seismic velocity and the point load strength. Three-dimensional X-ray Computed Tomography (CT) was used to obtain information on the internal structure of the rock specimen, and the representative unit length (LR) was calculated by applying a statistical technique to the CT images. We also proposed an estimation equation to predict the mechanical properties of rocks from the relationship between LR, acoustic velocity and point load strength. In the proposed method, it is shown that the characterization of internal structure of rocks could be utilized as an indirect index to account for the mechanical behavior of rocks by substituting physical laboratory testing for non-destructive test.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.93-104
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• 2004

This paper intended to assess the hydro-structure characteristics of volcanic rocks based on the hydrogeological data obtained from the underground storage cavern during construction. The variation of groundwater levels was periodically measured from the 28 surface monitoring holes(NX size) and the hydraulic pressures and injection rates were daily monitored from the water curtain holes(95 horizontal holes and 63 vertical holes). The hydraulic interference tests were performed in whole water curtain holes. The distribution patterns of hydraulic pressure are closely related to the dip angles of fracture intersected to the water curtain holes. Three domains can be grouped by the distribution of hydraulic pressures in the horizontal water curtain holes. The initial hydraulic pressures measured immediately after drilling of water crutain holes are high in ascending order of the cavern C-2, C-1, and C-3. The priliminary hydrochemical data also indicate that the portions of the deep groundwater composition is relatively great in the cavern C-3 area. Some of the horizontal water curtain holes in the cavern C-3 show a steady higher groundwater pressure with the composition of shallow groundwater indicating the outer boundary as constant hydraulic boundary. The water curtain holes in the cavern C-2 is characterized as low initial hydraulic pressure and less injection rates, suggesting poor hydraulic connectivity to a shallow groundwater system. The results of the study can help to understand a hydraulic compartment concept in a fracture hydro-geology and be utilized during the surface investigation for a groundwater system.

• Journal of Soil and Groundwater Environment
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• v.12 no.5
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• pp.19-32
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• 2007

In Korea, there have been various methods of estimating groundwater recharge which generally can be subdivided into three types: baseflow separation method by means of groundwater recession curve, water budget analysis based on lumped conceptual model in watershed, and water table fluctuation method (WTF) by using the data from groundwater monitoring wells. However, groundwater recharge rate shows the spatial-temporal variability due to climatic condition, land use and hydrogeological heterogeneity, so these methods have various limits to deal with these characteristics. To overcome these limitations, we present a new method of estimating recharge based on water balance components from the SWAT-MODFLOW which is an integrated surface-ground water model. Groundwater levels in the interest area close to the stream have dynamics similar to stream flow, whereas levels further upslope respond to precipitation with a delay. As these behaviours are related to the physical process of recharge, it is needed to account for the time delay in aquifer recharge once the water exits the soil profile to represent these features. In SWAT, a single linear reservoir storage module with an exponential decay weighting function is used to compute the recharge from soil to aquifer on a given day. However, this module has some limitations expressing recharge variation when the delay time is too long and transient recharge trend does not match to the groundwater table time series, the multi-reservoir storage routing module which represents more realistic time delay through vadose zone is newly suggested in this study. In this module, the parameter related to the delay time should be optimized by checking the correlation between simulated recharge and observed groundwater levels. The final step of this procedure is to compare simulated groundwater table with observed one as well as to compare simulated watershed runoff with observed one. This method is applied to Mihocheon watershed in Korea for the purpose of testing the procedure of proper estimation of spatio-temporal groundwater recharge distribution. As the newly suggested method of estimating recharge has the advantages of effectiveness of watershed model as well as the accuracy of WTF method, the estimated daily recharge rate would be an advanced quantity reflecting the heterogeneity of hydrogeology, climatic condition, land use as well as physical behaviour of water in soil layers and aquifers.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.143-149
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• 1997

암석의 파괴인성계수(fracture toughness)는 균열의 성장에 대한 암석의 저항을 나타낸다. 실험실에서 측정한 파괴인성계수는 일반적인 암석의 불균질성이나 이방성 외에도 시험편의 형상이나 하중조건에 의하여 크게 영향을 받는다. 따라서, 제한된 수의 시험편을 사용하여 측정된 파괴인성계수는 자료의 분산이 심하므로 실제 적용에 있어서 문제가 된다. 균열감응도란 파괴인성계수의 측정에 사용되는 시험편의 형상에 따라 결정되는 지수로서, 시험편의 파괴가 균열의 성장에 의한 것인지, 혹은 인장강도에 의한 것인지를 판별하는 기준이 된다. 이러한 균열감응도를 파악하여 암석의 파괴인성계수 측정에 유효한 시험편의 크기나 초기균열 길이의 범위를 설정할 수 있다. 이는 또한 실험실에서 측정된 차괴인성계수의 유효성 여부를 판별하는 기준으로 사용될 수 있다. 본 논문에서는 암석의 파괴인성계수의 측정에 흔히 사용되는 몇 가지 형태의 시험편들에 대하여 균열감응도를 계산하고 이에 따른 초기균열 길이의 범위를 제시하고자 한다.

• Journal of the Korean Geophysical Society
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• v.6 no.4
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• pp.261-268
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• 2003

Lots of various utilities are buried under the surface. The effective management of underground utilities is becoming the very important subject for the harmonious administration of the city. Ground Penetrating Radar(GPR) survey including other various underground survey methods, is mainly used to detect the position and depth of buried underground utilities. However, GPR is not applicable, under the circumstances of shallow depth and places, where subsurface materials are inhomogeneous and are composed of clay, salt and gravels. The aim of this study is to overcome these limitations of GPR and other underground surveys. High-frequency electromagnetic (HFEM) method is developed for the non-destructive precise deep surveying of underground utilities. The method is applied in the site where current underground surveys are useless to detect the underground big pipes, because of poor geotechnical environment. As a result, HFEM survey was very successful in detecting the buried shallow and deep underground pipes and in obtaining the geotechnical information, although other underground surveys including GPR were not applicable. Therefore this method is a promising new technique in the lots of fields, such as underground surveying and archaeology.

• Economic and Environmental Geology
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• v.23 no.4
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• pp.393-409
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• 1990

Synthetic seismograms and deduced characteristic properties of the non-geometrical $S^*$ and $P^*$ waves are presented. These waves are excited on the free surface or an interface between two different media by an inhomogeneous P wave from a point source nearby, and propagate as homogeneous waves in the media. Synthetic seismograms are computed using an extended reflectivity method designed for buried source and receiver. An efficient computational procedure for propagator matrices of layers is devised to reduce the computational time and the RAM memory size in the implementation of the reflectivity method. Radiation patterns are obtained from the particle motions of the four types of the "*" waves, i.e., the $S^*$ wave generated near the free surface, and the reflected $S^*$, transmitted $S^*$ and transmitted $P^*$ waves generated near an interface. Some patterns show polarity changes of displacements and others reveal monotonic or non-monotonic variation of amplitude depending on the velocity structure. The decaying trend of amplitude with increasing epicentral distance are also shown for the head wave type of the "*" waves.

• Journal of the Geological Society of Korea
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• v.54 no.5
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• pp.557-566
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• 2018

Pohang earthquake (Main shock magnitude = 5.4) occurred in Southeastern region of South Korea in November 15, 2017. Groundwater levels of 6 monitoring wells with 5 minutes interval measurements located in that region and stream water levels of 4 stations located along the Hyeongsan-gang stream are used for the analysis of earthquake induced effects. Four groundwater monitoring wells show a short-term decrease of groundwater level after a main shock and one well does an increase and the maximum change is about 42.0 cm. Especially, groundwater levels at two monitoring wells near the epicenter are consistently maintained after a decrease. There is little relationship between earthquake magnitude or a distance to epicenter and changing amount of groundwater level and it may be due to the inhomogeneity of geologic material and unconsolidated sediments distribution. The changes in permeability of fractured zone and groundwater levels occasionally cause changes in stream flow rate, and water level of the Hyeongsan-gang stream in the study area decreases just after the earthquake and increases again up to the normal level and next shows an more gentle decreasing slope. Total increasing flow rates at S1 (upstream site) and S4 (downstream site) stations are about $12,096m^3$ and $116,640m^3$, respectively, during the increasing period.