• Journal of Korean Tunnelling and Underground Space Association
• /
• v.26 no.5
• /
• pp.489-506
• /
• 2024

Excavation of tunnels below the groundwater table changes the hydraulic boundary conditions, causing flow towards the excavation face. Inflow into a tunnel is generally influenced by pre-excavation grouting, shotcrete lining, drainage system implementation, and the hydraulic deterioration of the drainage system. From the perspective of continuum theory, the groundwater inflow behavior due to excavation is very similar to the tunnel excavation behavior known as the convergence-confinement method. The groundwater inflow behavior due to tunnel excavation can be explained by the hydraulic convergence, while the behavior of shotcrete lining in limiting inflow can be inferred as hydraulic confinement. This study investigates the hydraulic convergence and confinement behavior using theoretical and numerical methods due to tunnelling. It is confirmed that the hydraulic convergence-confinement is exactly the same as the mechanical convergence-confinement concept. It is identified that the behavior is governed by the tunnel geometry, grout thickness and permeability, as well as the thickness and permeability of the support materials, such as shotcrete.

• Geotechnical Engineering
• /
• v.8 no.2
• /
• pp.5-20
• /
• 1992

The physical-based and lumped-parameter hydrologic groundwater flow model for predicting the rainfall-triggered rise of groundwater levels in hillside slopes is developed in this paper to assess the risk of landslides. The developed model consists of a vertical infiltration model for unsaturated zone linked to a linear storage reservoir model(LSRM) for saturated zone. The groundwater flow model has uncertain constants like soil depttL slope angle, saturated permeability, and potential evapotranspiration and four free model parameters like a, b, c, and K. The free model parameters could be estimated from known input-output records. The BARD algorithm is uses as the parameter estimation technique which is based on a linearization of the proposed model by Gauss -Newton method and Taylor series expansion. The application to examine the capacity of prediction shows that the developed model has a potential of use in forecast systems of predicting landslides and that the optimal estimate of potential 'a' in infiltration model is the most important in the global optimum analysis because small variation of it results in the large change of the objective function, the sum of squares of deviations of the observed and computed groundwater levels. 본 논문에서는 가파른 산사면에서 산사태의 발생을 예측하기 위한 수문학적 인 지하수 흐름 모델을 개발하였다. 이 모델은 물리적인 개념에 기본하였으며, Lumped-parameter를 이용하였다. 개발된 지하수 흐름 모델은 두 모델을 조합하여 구성되어 있으며, 비포화대 흐름을 위해서는 수정된 abcd 모델을, 포화대 흐름에 대해서는 시간 지체 효과를 고려할 수 있는 선형 저수지 모델을 이용하였다. 지하수 흐름 모델은 토층의 두께, 산사면의 경사각, 포화투수계수, 잠재 증발산 량과 같은 불확실한 상수들과 a, b, c, 그리고 K와 같은 자유모델변수들을 가진다. 자유모델변수들은 유입-유출 자료들로부터 평가할 수 있으며, 이를 위해서 본 논문에서는 Gauss-Newton 방법을 이용한 Bard 알고리즘을 사용하였다. 서울 구로구 시흥동 산사태 발생 지역의 산사면에 대하여 개발된 모델을 적용하여 예제 해석을 수행함으로써, 지하수 흐름 모델이 산사태 발생 예측을 위하여 이용할 수 있음을 입증하였다. 또한, 매개변수분석 연구를 통하여, 변수 a값은 작은 변화에 대하여 목적함수값에 큰 변화를 일으키므로 a의 값에 대한 최적값을 구하는 것이 가장 중요한 요소라는 결론을 얻었다.

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

• Journal of Korea Water Resources Association
• /
• v.31 no.3
• /
• pp.347-360
• /
• 1998

Numerical simulations for fluid flow and solute transport in a fracture rock masses are performed by using a transient flow model, which is based on the three-dimensional stochastic and discrete fracture network model (DFN model) and is coupled hydraulic model with mechanical model. In the numerical simulations of the solute transport, we used to the particle following algorithm which is similar to an advective biased random walk. The purpose of this study is to predict the response of the tracer test between two deep bore holes (GPK1 and GPK2) implanted at Soultz sous Foret in France, in the context of the geothermal researches.l The data sets used are obtained from in situcirculating experiments during 1995. As the result of the transport simulation, the mean transit time for the non reactive particles is about 5 days between two bore holes.

• Journal of Korean Society of Forest Science
• /
• v.108 no.2
• /
• pp.233-240
• /
• 2019

The aim of this study was to provide basic data that could identify and help prevent a slow-moving landslide using an analysis of the relationship between below-ground characteristics and water from three slow-moving landslide areas in Pohang, Gyeongsangbuk-do, South Korea. Surface surveys, resistivity, seismic exploration, well logging, and boring surveys were conducted in the three areas. The main direction of discontinuous surface was matched with the slope direction of the three landslides. The results indicatedthat slow-moving landslides might occur in the direction of the slope. Underground water was distributed within the crush zones within the three landslide areas and flowed along the tensile cracks. There was a significant difference (p<0.01) between the mean angle of the tensile cracks and that of the underground waterflow (p=0.8019). These results indicated that the progress of a slow-moving landslide can be forecast by monitoring the location and flow of underground water within a known slow-moving landslide area.

• Economic and Environmental Geology
• /
• v.30 no.2
• /
• pp.137-142
• /
• 1997

At the tailings dam of the disused Brukunga pyrite mine in South Australia, reaction of groundwater with the tailings causes the formation and discharge of sulphuric acid. There is a need to improve remediation efforts by decreasing groundwater flow through the tailings dam. Geophysical methods have been investigated to determine whether they can be used to characterise variations in depth to watertable and map preferred groundwater flow paths. Three methods were used: transient electromagnetic (TEM) soundings, direct current (DC) soundings and profiling, and self potential (SP) profiling. The profiling methods were used to map the areal extent of a given response, while soundings was used to determine the variation in response with depth. The results of the geophysical surveys show that the voltages measured with SP profiling are small and it is hard to determine any preferred channels of groundwater flow from SP data alone. Results obtained from TEM and DC soundings, show that the DC method is useful for determining layer boundaries at shallow depths (less than about 10 m), while the TEM method can resolve deeper structures. Joint use of TEM and DC data gives a more complete and accurate geoelectric section. The TEM and DC measurements have enabled accurate determination of depth to groundwater. For soundings centred at piezometers, this depth is consistent with the measured watertable level in the corresponding piezometer. A map of the watertable level produced from all the TEM and DC soundings at the site shows that the shallowest level is at a depth of about 1 m, and occurs at the southeast of the site, while the deepest watertable level (about 17 m) occurs at the northwest part of the site. The results indicate that a possible source of groundwater occurs at the southeast area of the dam, and the aquifer thickness varies between 6 and 13 m. A map of the variation of resistivity of the aquifer has also been produced from the TEM and DC data. This map shows that the least resistive (i.e., most conductive) section of the aquifer occurs in the northeast of the site, while the most resistive part of the aquifer occurs in the southeast. These results are interpreted to indicate a source of fresh (resistive) groundwater in the southeast of the site, with a possible further source of conductive groundwater in the northeast.

• Journal of Korean Society for Geospatial Information Science
• /
• v.24 no.4
• /
• pp.13-19
• /
• 2016

This study presented the build-up of three-dimensional soil pollution map for precise analysis. To do this, survey on the existing pollutant region on Dongnae-gu, Busan that is the study subject, showed that it tended to produce 0.72 clusters. So, this study suggested to investigate center of $1km{\times}1km $ grid and, as the results of comparing the pollution map that input pollution figure values based on the actually investigation point showed precise results. And, it divided the standard of pollution into 5 levels in surface and underground space and the map was built up using IDW interpolation against the amount of polluted substance. The pollution of ground surface, flow of polluted substance, coefficient of permeability and ground water level that are 504 geotechnical informations were selected as the influential parameters in pollution analysis of underground space, and it calculated that to 0~20 points by dividing the characteristics. It enables the build-up of pollution map of ground surface-underground with depth that considers the characteristics of soil layers and it is considered that it is possible to analyze the general infiltration. And, it was considered that it enables more accurate forecast about influential analysis per depth and pollution of underground water.

• Korean Security Journal
• /
• no.41
• /
• pp.185-212
• /
• 2014

This research examines the decentralization of al-Qaida and other Salafi-jihadist terrorist groups, which is a subject of intense debate in the West. Especially, this study focused on investigating the status and evolution of al Qa'ida and other two Salafi-jihadist groups, Boko Haram and the Islamic States. These terrorist groups are currently considered as the most active Salafi-jihadist terrorist groups leading today's decentralization from Al-Qaida central terrorism network. This study also aims to examine the contemporary threats posed by the two extremely violent jihadist terrorist groups and these groups's terrorist networks. In order to achieve the purpose of this study, this study conducted content analyses with a wide range of documents reporting about Salafi-jihadist terrorists groups. Also this study utilized GTD data set drwan from START centner to provide descriptive analyses regarding IS and Boko Haram's activities and threats. On the basis of analyses, this study argues that recently the threats posed by core al Qaida has been severely weakened. Further, the broader Salafi-jihadist movement has become more decentralized among four tiers: first, core al Qaida in Pakistan; second, formal al Qa'ida affiliated groups that have sworn allegiance to core al Qaida; a number of Salafi-jihadist groups that have committed to establishing an extremist Islamic emirate without sworn allegiance to al Qaida; third, individual followers and networks inspired by al Qaida and other Salafi-jihadist groups. In concusion and discussion, this study highlights the need for a long-term engagement counter terrorism strategy against Salifi-jihadist terrorists groups on behalf of the peace and security of the world society.

• Journal of the Mineralogical Society of Korea
• /
• v.19 no.4 s.50
• /
• pp.239-246
• /
• 2006

KAERI Underground Research Tunnel (KURT) was recently constructed through the site investigation from the yea. of 2003 at KAERI site, Dukjin-dong, Yuseong-gu, Daejeon city. The geo-logic setting of the site has been slightly metamorphosed. There are small fractures developed in the rock and several kinds of secondary filling minerals exist in the fractures. We examined mineralogical characteristics of fracture-filling calcite, which is not only largely distributed, but also can significantly affect the radionuclides migration. The calcite is found along fractures like other secondary minerals, forming thick veins in part. Most calcite-filled fractures contain quartz, iron oxides, and dolomite as minor minerals. The calcite crystals show an characteristic appearance with an uniformly oriented growth, coated with goethite on the edge and the etch-pit sites of their surface. Some calcite crystals have been newly formed by the precipitation of elements dissolved from the tunnel shotcrete wall, and their morphology changed according to the chemistry and flow of groundwater. The calcite can modify the groundwater chemistry and significantly affect the sorption behavior of radionuclides. The characteristic crystal structure and surface morphology of the calcite examined in the KURT site will be used as important basic data for the radionuclide migration experiment in the future.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2019.05a
• /
• pp.362-362
• /
• 2019

제주도는 화산섬의 지질특성상 지표수의 개발이용여건이 취약한 관계로 용수의 대부분을 지하수에 의존하고 있다. 따라서 제주도는 정책 및 연구적으로 오랜 기간 동안 지하수의 보전관리에 많은 노력을 기울여 오고 있다. 하지만 최근 기후변화로 인한 지하수위의 하강 및 해수면 상승으로 인한 해수침투의 문제가 꾸준히 제기되고 있으며, 제주도 일부지역에서는 축산폐수 등으로 인해 지하수의 수질오염문제가 발생하고 있다. 따라서 제주도 지하수의 수량 및 수질에 대한 체계적인 관리의 필요성이 증대되고 있다. 지하수에 절대적으로 의존하고 있는 제주도의 수자원의 개발 및 이용 여건을 고려할 때, 지하수의 수량 및 수질에 대한 학술적 토대가 확고히 구축되어야 할 뿐만 아니라 기후변화에 대응한 최적 물관리기법의 개발이 필요한 실정이다. 하지만 제주도의 수자원에 대한 기존의 연구들은 제주도 전역에 대해 최신의 분석방법을 사용한 종합적인 연구가 아닌 일부지역을 대상으로 한 지하지질분석, 지구물리탐사 및 대수성시험 위주의 단편적 분석, 개념적 수문모델의 적용에 의한 대략적인 분석, 또는 일부지역을 대상으로 한 지하수 흐름분석 및 해수침투 분석 위주로 수행되었다. 이러한 기존의 연구들은 여러 가지 문제점을 내포하고 있는데 첫째, 일부지역의 지하지질이 제주도의 복잡한 지하지질특성을 대표할 수 없다는 점과 둘째, 개념적 수문모델은 제주도와 같이 강우의 큰 시공간적 변동성을 고려할 수 없으며 지하지질 특성의 공간적 변동성 또한 적절히 반영할 수 없다는 점 및 셋째, 지하수의 이동은 유역경계와 일치하지 않으므로 독립된 소유역을 대상으로 산정한 지하수 부존량은 소유역내 실제 지하수 부존량과 다를 수 있다는 점 그리고 마지막으로 개별적으로 수행된 지표수, 지하수 및 수질 분석들은 서로 연결성이 없어 이들 간의 상호작용을 고려하지 않아 그 결과의 신뢰성이 떨어진다는 점 등이다. 이러한 제주도에 대한 기존 연구들의 한계점을 극복하기 위해서는 제주도 전역에 대한 종합적인 연구가 필요하다. 이를 위한 방안으로서 제주도 전체를 대상으로 한 최신의 분포형 수문모델의 구축이 필요하며 이 수문모델은 지표수 및 지하수의 상호작용과 해수침투 및 수질 또한 모의할 수 있어야 할 것이다. 그리고 이 개발된 모형과 기후변화 시나리오를 사용하여 미래 수자원변화에 대한 대응이 필요하다. 이에 대한 해외연구사례로서 미국지질조사국이 하와이 섬들 및 괌 등에 대해 수행했던 연구들을 참고할 수 있다. 제주도 전체에 대한 신뢰할만한 종합적인 분석결과는 제주도 수자원의 정책수립에 기초로 활용할 수 있을 것이다.