Hydraulic conductivity is a critical design parameter for buffers in high-level radioactive waste repositories. Most employed prediction models for hydraulic conductivity are limited to various types of bentonites, the main material of the buffer, and the associated temperature conditions. This study proposes the utilization of a novel integrated prediction model. The model is derived through theoretical and regression analyses and is applied to all types of compacted bentonites when the relationship between hydraulic conductivity and dry density for each compacted bentonite is known. The proposed model incorporates parameters such as permeability ratio, dynamic viscosity, and temperature coefficient to enable accurate prediction of hydraulic conductivity with temperature. Based on the results obtained, the values are in good agreement with the measured values for the selected bentonites, demonstrating the effectiveness of the proposed model. These results contribute to the analysis of the hydraulic behavior of the buffer with temperature during periods of high-level radioactive waste deposition.

In the design of HLW repositories, it is important to confirm the performance and safety of buffer materials at high temperatures. Most existing models for predicting hydraulic conductivity of bentonite buffer materials have been derived using the results of tests conducted below 100°C. However, they cannot be applied to temperatures above 100°C. This study suggests a prediction model for the hydraulic conductivity of bentonite buffer materials, valid at temperatures between 100°C and 125°C, based on different test results and values reported in literature. Among several factors, dry density and temperature were the most relevant to hydraulic conductivity and were used as important independent variables for the prediction model. The effect of temperature, which positively correlates with hydraulic conductivity, was greater than that of dry density, which negatively correlates with hydraulic conductivity. Finally, to enhance the prediction accuracy, a new parameter reflecting the effect of dry density and temperature was proposed and included in the final prediction model. Compared to the existing model, the predicted result of the final suggested model was closer to the measured values.

고준위방사성폐기물의 처분은 고심도 암반내에 처분시스템을 구축하는 심층 처분방법이 고려된다. 심층 처분은 처분용기, 완충재, 뒷채움재, 근계암반의 설계 요소인 공학적방벽과 천연 방벽으로 구성된다. 공학적방벽 중에서 벤토나이트 완충재는 암반으로부터 유입되는 지하수 흐름을 최소화하고 핵종 유출을 저지하는 기능을 한다. 지하수 유입으로 인한 완충재의 수리전도도 특성 규명은 처분장 공학적방벽의 안정성 및 건전성에 대한 성능 평가에 있어 중요한 사안이다. 본 연구에서는 경주 벤토나이트를 이용하여 다양한 건조밀도와 온도 조건에 따라 포화 수리전도도 실험을 수행하였으며, 120개의 실험 결과 를 다중 회귀 분석을 통해 수리전도도 추정 모델을 제시하였다. 실험 결과에서는 건조밀도가 커질수록 수리전도도가 감소하는 경향이 나타났다. 또한, 온도가 증가할수록 수리전도도가 증가하였다. 이러한 실험 결과들을 종합한 다중 회귀 분석 결과에서는 수리전도도 추정식의 결정계수(R2)가 0.93으로 높게 나타났다. 본 연구에서 제시된 수리전도도 추정식은 벤토나이트 완충재의 성능과 연관된 건조밀도와 온도의 영향을 고려하여 처분시스템의 공학적방벽 설계에 활용 될 것으로 판단된다.

Hydraulic and drainage properties play an important role in the serviceability of a permeable block pavement system. A serious impediment to its performance is the accumulation of sediments over time. The deposition of these particles in block pavement joints reduces infiltration rate and drainage capacity, which, in the long run, decreases the system’s life span. In this study, laboratory experiments were conducted in order to investigate the influence of particle deposition on the hydraulic conductivity of a type of block pavement system, permeable stone paver, without maintenance or cleaning. Coefficients of permeability before and after addition of fine particles were evaluated using a developed permeability equipment with constant head frame. Three gradations of silica sand were used to simulate road clogging particles. An equivalent of eight years of sediment loading was applied to three identical permeable pavement samples. Laboratory test results showed an average of 77% reduction on the permeability due to particle accumulation.

상대습도 데이터를 이용하여 벤토나이트 완충재 블록의 불포화 수리전도도 변화를 평가하였다. 불포화 매질에서의 물의 흐 름을 나타내는 일반적인 분석해를 통해 상대습도를 통한 불포화 수리전도도 계산방안을 도출하였고, 이를 실제 수행한 실 내 물 유입 실험 결과에 적용하여 포화가 진행됨에 따라 변화하는 완충재 불포화 수리전도도 양상을 확인하였다. 일반적인 포화 상태와는 확연히 다르게 수두 구배와 물의 유출량이 시간에 따라 불규칙하게 변화하는 결과를 나타냈으며, 벤토나이 트 완충재의 불포화 수리전도도는 시간에 따라 증가하는 경향을 보였다. 수분 흡수로 인한 벤토나이트 입자 팽창 때문으로 인한 매질 내 공극의 부피 및 크기 확대가 불포화 수리전도도값의 증가를 야기하는 것으로 판단되었고, 이러한 결과는 완 충재 블록의 팽창 정도와 수리전도도의 상관성에 관한 추후 연구의 필요성을 제시하였다. 본 연구에서 수행된 불포화 수리 전도도 평가 방안은 방사성폐기물 처분 시 완충재의 장기적인 수리학적 성능평가에 유용한 기술로 사용될 수 있을 것이다.

PURPOSES : This study is to construct the regression models of drainage asphalt concrete specimens and to provide the appropriate coefficients of hydraulic conductivity prediction models. METHODS: In terms of easy calculation of the hydraulic conductivity from porosity of asphalt concrete pavement, the estimation model of hydraulic conductivity was proposed using regression analysis. 10 specimens of drainage asphalt concrete pavement were made for measurement of the hydraulic conductivity. Hydraulic conductivity model proposed in this study was calculated by empirical model based on porosity and the grain size. In this study, it shows the compared results from permeability measured test and empirical equation, and the suitability of proposed model, using regression analysis. RESULTS: As the result of the regression analysis, the hydraulic conductivity calculated from the proposal model was similar to that resulted from permeability measured test. Also result of RMSE (Root Mean Square Error) analysis, a proposed regression model is resulted in more accurate model. CONCLUSIONS: The proposed model can be used in case of estimating the hydraulic conductivity at drainage asphalt concrete pavements in fields.

다양한 건조밀도를 가진 압축벤토나이트의 수리전도도에 물의 염도가 미치는 영향이 조사되었다. 압축벤토 나이트의 수리전도도는 벤토나이트의 건조밀도가 상대적으로 낮은 경우에만, 염도가 증가함에 따라 증가하였 으며, 염도의 증가에 따른 수리전도도의 증가 정도는 벤토나이트의 건조밀도가 낮을수록 더 현저하였다. 건조 밀도가 1.0 Mg/m3 및 1.2 Mg/m3 인 압축벤토나이트의 경우, 0.4 M NaCl 용액의 수리전도도는 탈염수의 경우 에 비해 각각 7배 및 3배가 증가하였다. 그러나 1.4 Mg/m3 보다 큰 건조밀도를 가진 압축벤토나이트의 경우에 는, 수리전도도에 미치는 염도의 영향이 크지 않았으며, NaCl의 농도가 0.04 M에서 0.4 M 인 범위에서는 거의 일정한 값을 유지하였다. 벤토나이트 시편을 탈염수로 미리 포화시키는 것은 수리전도도에 큰 영향을 미치지 않았다.

The relationship between hydrologic processes and scale is one of the more complex issues in surface water hydrology. Disturbances that change vegetation and/or soil properties have been known to subsequently alter the landscape. The primary objective of this study was to estimate the grain size of soils with different properties from the hydraulic conductivity using pedotransfer functions. The double ring infiltrometer method was used to measure the vertical hydraulic conductivity of three soils under different soil planar surface treatments. Seven selected pedotransfer functions were used to estimate percentile diameters and the reduction in infiltration caused by compaction was misconstrued as caused by changes in percentile diameter. Results showed that compaction on the sandy loamy foot paths reduced the hydraulic conductivity by about 50%. The study showed that perceptual models of infiltration processes and appreciation of scale problems in modeling are far more sophisticated than normally presented in texts. Hydraulic measurement methods are still relevant and will provide significant information of grain size of the soils.

We used numerical models to reliably analyze the groundwater flow and hydraulic conductivity on Jeju Island. To increase reliability, improvements were made to model application factors such as hydraulic watershed classification, groundwater recharge calculation by precipitation, hydraulic conduction calculation using the pilot point method, and expansion of the observed groundwater level. Analysis of groundwater flow showed that the model-calculated water level was similar to the observed value. However, the Seogwi and West Jeju watersheds showed large differences in groundwater level. These areas need to be analyzed by segmenting the distribution of the hydraulic conductivity. Analyzing the groundwater flow in a sub watershed showed that groundwater flow was similar to values from equipotential lines; therefore, the reliability of the analysis results could be improved. Estimation of hydraulic conductivity distribution according to the results of the groundwater flow simulation for all areas of Jeju Island showed hydraulic conductivity > 100 m/d in the coastal area and 1 45 m/d in the upstream area. Notably, hydraulic conductivity was 500 m/d or above in the lowlands of the eastern area, and it was relatively high in some northern and southern areas. Such characteristics were found to be related to distribution of the equipotential lines and type of groundwater occurrence.

In this study, the sensitivity analysis of hydraulic conductivity and separation distance (distance between injection well and pumping well) was analyzed by establishing a conceptual model considering the hydrogeologic characteristics of facility agricultural complex in Korea. In the conceptual model, natural characteristics (topography and geology, precipitation, hydraulic conductivity, etc.) and artificial characteristics (separation distance from injection well to pumping well, injection rate and pumping rate, etc.) is entered, and sensitivity analysis was performed 12 scenarios using a combination of hydraulic conductivity (10-1 cm/sec, 10-2 cm/sec, 10-3 cm/sec, 10-4 cm/sec) and separation distance (10 m, 50 m, 100 m). Groundwater drawdown at the monitoring well was increased as the hydraulic conductivity decreased and the separation distance increased. From the regression analysis of groundwater drawdown as a hydraulic conductivity at the same separation distance, it was found that the groundwater level fluctuation of artificial recharge aquifer was dominantly influenced by hydraulic conductivity. In the condition that the hydraulic conductivity of artificial recharge aquifer was 10-2 cm/sec or more, the radius of influence of groundwater level was within 20 m, but In the condition that the hydraulic conductivity is 10-3 cm/sec or less, it is confirmed that the radius of influence of groundwater increases sharply as the separation distance increases.

In this study, groundwater flow was analyzed targeting Dae-jeong watershed, which exhibited the largest variations of groundwater levels at the identical elevation points among the 16 watersheds of Jeju Island. The issues of the methods applied in practice were identified and improvement plans were suggested. This groundwater-flow estimates derived by applying hydraulic conductivity values onto zones of equal topographic ground level were found to be quite different from actual measured groundwater flow. Conversely, groundwater-flow estimates that utilized hydraulic conductivity values applied onto groundwater-level equipotential lines indicated relatively lesser divergences from actual measured groundwater flow. The reliabilities of the two approaches were assessed for 60 randomly selected points on DEM (digital elevation model) maps, The method using hydraulic conductivity values applied onto groundwater-level contours turned out to be the more reliable approach for the Dae-jeong watershed in Jeju Island.