• The Journal of Engineering Geology
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• v.13 no.1
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• pp.17-27
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• 2003

In this study, a phenomenon of saltwater intrusion was monitored under various conditions regarding recharge and pumping rate using time domain reflectometry for a laboratory scale unconfined aquifer to verify the basic theory behind seawater intrusion and to investigate movement of salt-freshwater interface in accordance with the ratio of pumping and recharge rate. Results showed that a thick mixing zone was formed at the boundary instead of a sharp salt-freshwater interface that was assumed by Ghyben and Herzberg who derived an equation relating the water table depth $(H_f)$ to the depth to the interface $(H_s)$. Therefore our experimental results did not agree with the calculated values obtained from the Ghyben and Herzberg equation. Position of interface which was adopted as 0.5 g/L isochlor moved rapidly as the Pumping rate $(Q_p)$ increased for a given recharge rate $(Q_r)$. In addition, interface movement was found to be about 7 times the ratio of $Q_p/Q_r$ in our experimental condition. This indicates that Pumping rate becomes an important factor controlling the seawater intrusion in coastal aquifer.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.417-425
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• 2019

Agricultural groundwater use accounts for 51.8% of total groundwater use, so accurate estimation of groundwater use is important for efficient groundwater management. The purpose of this study is to develop a method for estimating the groundwater use of agricultural (rice farming and dry-field farming) wells using regression tree model based on the measured data of 370 wells. Three input variables of the model were evaluated as being significant: well depth, pipe diameter, and pump capacity, and the importance of each variable was 75% for well depth, 17% for pipe diameter, and 8% for pumping capacity. The daily usage of agricultural (rice farming and dry-field farming) wells by the regression tree model was estimated to be very similar to the actual usage, compared to the previous estimation method proposed by the Ministry of Construction and Transportation. In the future, it is expected that the reliability of the usage statistics will be improved if additional observed data is secured and this classification method is modified.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.253-268
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• 2020

In this study, recharge rates are estimated using SWAT-K (a distributed hydrological model). The validity of the estimated recharge rates were evaluated by employing the baseflow separation method based on observed hydrological data. The exploitable groundwater is typically determined as the 10-year drought frequency recharge rate that is calculated by average recharge ratio multiplied by 10-year drought frequency precipitation. In practice, however, recharge rates typically decrease in line with precipitation; therefore, exploitable groundwater could be overestimated when average recharge rates are used without considering precipitation. To resolve this overestimation, exploitable groundwater was calculated by re-estimating recharge rates that consider precipitation intensity. By applying this method to the Uiwang, Gwacheon, and Seongnam sub-basins, the exploitable groundwater decreased by 55.5~77.6%, compared with recharge rates obtained using the existing method.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.275-282
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• 2006

This study was conducted laboratory flume tests to identify landslide features and flow characteristics of debris using a flume test equipment. Under the several test conditions dependent on rainfall intensity and slope angle, the authors measured pore water pressure, slope failure and displacement, spreading area of debris on a regular time interval. The test processes were also recorded by video cameras and digital still cameras. According to the test results, pore water pressures have trends of direct proportion to the rainfall intensity and the slope angle, resulting in high potential of landslide triggering. The spreading area of debris is also increased with the slope angle and the rainfall intensity as well as the rainfall duration.

• The Journal of Engineering Geology
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• v.25 no.3
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• pp.331-337
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• 2015

A new technique is presented to detect unstable slope behavior, based on Hotelling's T² analysis of pore pressure and water content obtained during flume tests using granitic and gneissic weathered soils. Three sets of pore pressure-water content values were simultaneously obtained during each test, and T² statistics at the 90.0% and 95.0% confidence levels were calculated based on the correlations between values. The results show that unsuccessful detection of some local failures of the flume slope depended on the sensor position. In the case of global slope failures, anomalous behavior was detected between several hundred and several thousand seconds before the event as T² statistics exceeded the confidence interval 90%. Hotelling's T² analysis provides a single control criterion because it enables correlations between diverse measured values within the same slope; the criterion also includes stepwise criteria for a forecasting and warning system based on confidence levels.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.326-326
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• 2016

The fault can be defined, in a geological context, as a rupture plane showing a significant displacement generated in the case that the local tectonic stress exceeds a threshold of rupture along a particular plane in a rock mass. The hydrogeological properties of this fault can be varied with the spatial distribution and the connectivity of void spaces in a fault. When the formation of fault includes the process of the creation and the destruction of void spaces, a complex relation between the displacement along the fault and the variation of void spaces. In this study, the variation of flow with the geometrical characteristics of the fault is simulated and analyzed by using the three-dimensional discrete fracture network model. Three different geometrical characteristics of the faults are considered in this study: 1) simple hydraulic conductive plane, 2) damaged zone, and 3) relay structure of faults.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.663-671
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• 2020

Recently, there have been many natural disasters in Korea, not only in forest areas but also in urban areas, and the national requirements for them are increasing. In particular, there is no pre-disaster information system that can systematically manage the collapse of the slope of the national highway. In this study, big data analysis was conducted on the factors causing slope collapse based on the detailed investigation report on the slope collapse of national roads in Gangwon-do and Gyeongsang-do areas managed by the Cut Slope Management System (CSMS) and the basic survey of slope failures. Based on the analysis results, a slope collapse risk prediction model was established through Adaboost, a classification-based machine learning model, reflecting the collapse slope location and weather information. It also developed a visualization map for the risk of slope collapse, which is a visualization program, to show that it can be used for preemptive disaster prevention measures by identifying the risk of slope due to changes in weather conditions.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.263-277
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• 2024

The availability of groundwater in the Yeoncheon area, South Korea, was estimated using the distributed hydrological model SWAT-K to calculate recharge rates based on land use and soil distribution. Model calibration and validation results were consistent between observed and simulated streamflows, with coefficients of determination of 0.75~0.97. Calculated groundwater recharge rates varied temporospatially, with lower rates in winter and spring than in summer. Estimated recharge rates were compared with the baseflow index of natural streamflow to assess the validity of estimated recharge amounts. Groundwater development potential was determined by calculating the recharge amount for a 10-year period by statistical frequency analysis, confirming it to be 11.5% of annual precipitation.

• The Journal of Engineering Geology
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• v.25 no.3
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• pp.377-385
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• 2015

We constructed a model test apparatus to evaluate the dependence of the saturation velocity (V_s) in soils on rainfall intensity (I_R). The apparatus comprises a soil box, a rainfall simulator, and measuring sensors. The model grounds (60 cm × 50 cm × 15 cm) were formed by Joomunjin standard sand with a relative density of 75%. The rainfall simulator can control the rainfall intensity to reenact the actual rainfall in a soil box. Time Domain Reflectometer (TDR) sensors and tensiometers were installed in the soils to measure changes in the volumetric water content and matric suction due to rainfall infiltration. During the tests, the soil saturation was determined by raising the groundwater table, which was formed at the bottom of the soil box. [Please check that the correct meaning has been maintained.] The wetting front did not form at the ground surface during rainfall because the soil particles were uniform and the coefficient of permeability was relatively high. Our results show that the suction stress of the soils decreased with increasing volumetric water content, and this effect was most pronounced for volumetric water contents of 20%-30%. Based on a regression analysis of the relationship between rainfall intensity and the average saturation velocity, we suggest the following equation for estimating the saturation velocity in soils: V_savg (cm/sec) = 0.068I_R (mm/hr).

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.381-387
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• 2013

In compiling flood hazard maps for the case of dam-failure, a scenario-based numerical modeling approach is commonly used, involving the modeling of important parameters that capture peak discharge, such as breach formation and progress. In this study, an earth-dam-break model is constructed assuming an identical mechanism and hydraulic process for all dam-break processes. A focus of the analysis is estimation of the hydrograph at the outlet as a function of time. The constructed hydrograph then serves as an upper boundary condition in running the flood routing model downstream, although flood routing is not considered here. Validation was performed using the record of the Tangjishan dam-break in China. The results were satisfactory, with a coefficient of determination of 0.974, Nash-Sutcliffe Coefficient of Efficiency (NSC) of 0.94, and Root Mean Square Error (RMSE) of $610m^3/sec$. The proposed model will contribute to assessments of potential flood hazards caused by dam-break.