• Geomechanics and Engineering
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• 제23권5호
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• pp.419-429
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• 2020

To investigate the effect of spatial variability on hydraulic properties of unsaturated soils, a numerical model is set up which can simulate seepage process in an unsaturated heterogeneous soil. The unsaturated heterogeneous soil is composed of matrix sand embedded with a small proportion of clay for simulating the heterogeneity. Soil-water characteristic curve and unsaturated hydraulic conductivity curve of the unsaturated soil are expressed by Van Genuchten model. Hydraulic parameters of the matrix sand are considered as random fields. Different autocorrelation lengths (ACLs) of hydraulic parameter of the matrix sand and different proportions of clay are assumed to investigate the influence of spatial variability on the equivalent hydraulic properties of the heterogeneous soil. Four model sizes are used in the numerical experiments to investigate the influence of scale effects and to determine the sizes of representative volume element (RVE) in the numerical simulations. Through a number of Monte Carlo simulations of unsaturated seepage analysis, the means and the coefficients of variations (COVs) of the equivalent hydraulic parameters of the heterogeneous soil are calculated. Simulations show that the ACL and model size has little influence on the means of the equivalent hydraulic parameters, but they have a large influence on the COVs of the equivalent hydraulic parameters. The size of an RVE is mainly affected by the ACL and the proportion of heterogeneity. The influence of spatial variability on the hydraulic parameters of the heterogeneous unsaturated soil can be used as a guidance for geotechnical reliability analysis and design related to unsaturated soils.

• Geomechanics and Engineering
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• 제20권3호
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• 한국수자원학회논문집
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• 제35권1호
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• pp.65-75
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• 2002

본 연구에서는 TOPMODEL의 매개변수 m, $T_{0}$에 따른 토양수분 변동성을 검토하고, 일단위 관측 지하수위자료를 이용하여 모형내 포화층에서의 흐름인 지하유출과의 상대적 비교 및 유역출구에서의 관측유량 및 계산유량을 비교하여 TOPMODEL의 토양수분 모의 능력을 규명하였다. 이를 위해 국제수문개발계획(IHP)의 평창강 상류 상안미 유역을 대상으로 94~98년 사이의 여름철 호우사상과 지하수위자료를 선택하였다. 매개변수 m, $T_{0}$에 따른 TOPMODEL의 토양수분 변동성은 토양내 지하수면의 유효깊이를 나타내는 m이 증가할수록 토양수분 보유능력이 증가하고, 특히 큰 값의 $T_{0}$와 결합되면 이러한 현상이 현저한 것으로 나타났다. 모형에 의해 산정된 지하유출과 실측 지하수위자료를 상대적으로 비교한 결과 첨두량이 유사하게 지체되는 경향으로 나타났으며, 강우가 끝난 후의 수문곡선 하강부는 대부분이 지하유출에 기인하고 있음을 잘 표현하고 있다. 따라서 TOPMODEL은 유역 출구에서의 유출량 산정뿐 아니라 유역의 토양수분 변화 모의에도 적합한 것으로 판단된다.

• Geomechanics and Engineering
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• 제34권3호
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• pp.317-328
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• 2023

The soil behaviour can be represented by numerical modelling of element testing using diverse constitutive models. However, not all constitutive models allow the simulation of the stress-strain response at the critical state in granular soils with both contractive and dilative behaviour. Moreover, the accuracy of these models depends highly on the quality of the experimental data used for their calibration. This study addresses the modelling of the critical state behaviour of an alluvial natural soil from the Lower Tagus Valley (south of Portugal), known as TP-Lisbon sand, using the NorSand constitutive law. For this purpose, a series of numerical simulations of element testing was carried out using two algorithms performed in Visual Basic (VB) and Fast Lagrangian Analysis of Continua (FLAC). Moreover, this study presents the characterisation of of NorSand parameters from an accurate experimental programme based on triaxial and bender element testing. This experimental program allowed defining: (i) the critical state locus, (ii) the stress-dilatancy, and (iii) the soil elasticity of TP-Lisbon sand -all fundamental to calibrate the contractive and dilative behaviour of such alluvial soil. The results revealed a good agreement between experimental data and NorSand simulations using VB and FLAC. Therefore, this study showed that the quality of laboratory testing procedures and its good interpretation enables NorSand constitutive law to capture representatively the non-associated plastic strains, often expressed by the state parameter, allowing a representation of soil behaviour of alluvial soils within the critical state soil mechanics framework for different state parameters.

• 대한토목학회논문집
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• 제34권5호
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• pp.1443-1454
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• 2014

본 연구는 레이더 강우와 분포형 수문모형의 공간해상도가 매개변수 추정 및 강우-유출 모의에 미치는 영향을 분석하였다. 레이더 강우는 비슬산 S밴드 이중편파 강우레이더에서 2012년 관측된 강우사상을 대상으로, R-KDP, R-Z, R-ZDR의 관계식에 의해 추정된 레이더 강우를 지상관측 강우와 비교하였다. 세 가지 강우 추정식에 의한 레이더 강우를 지상 관측 강우와 비교 시 유역 평균에 대해서는 모두 높은 일치도를 보였으며, 이는 지상 관측 강우에 대한 레이더 강우 보정의 영향으로 판단되었다. 그 중에서도 R-KDP에 의한 추정 강우가 비교적 높은 정확도를 보였으며, 이를 강우-유출 모형의 입력자료로 적용하였다. 강우-유출 모형으로는 GRM (grid based rainfall-runoff model) 모형을 이용하여, 낙동강 수계 금호강 유역을 대상으로, 200m, 500m, 1000m의 공간해상도로 입력자료를 구축하였다. 또한, 범용 매개변수 최적화 모형인 PEST(model independent parameter estimation tool)로 초기 포화도, 지표면 조도계수 및 토양 투수계수의 보정계수를 각 공간해상도 및 호우사상 별로 추정하였다. 매개변수 추정 결과, 200m 공간해상도 모형에서는 비교대상 강우사상에 대해 지표면 조도계수와 토양 투수계수 관련 보정계수가 비교적 안정적으로 추정되었으나, 500m, 1000m 공간해상도 모형에서는 강우사상에 따라 매개변수의 최적 추정 값의 변동이 확인되었다. 초기 포화도는 강우사상 별, 공간해상도 별로 일정한 경향을 보이지 않았다. 또한, 200m와 1000m 공간해상도에 대해 최적화된 매개변수를 다른 공간해상도에 적용한 결과, 1000m 공간해상도에 대해 보정된 매개변수를 200m 공간해상도 모형에 적용하면 첨두 홍수량이 증가하는 경향이 있었다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.217-217
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• 2015

The objective of this study was mainly to evaluate the water resources potential of Lake Tana Basin (LTB) by using Soil and Water Assessment Tool (SWAT). From SWAT simulation of LTB, about 5236 km2 area of LTB is gauged watershed and the remaining 9878 km2 area is ungauged watershed. For calibration of model parameters, four gauged stations were considered namely: Gilgel Abay, Gummera, Rib, and Megech. The SWAT-CUP built-in techniques, particle swarm optimization (PSO) and generalized likelihood uncertainty estimation (GLUE) method was used for calibration of model parameters and PSO method were selected for the study based on its performance results in four gauging stations. However the level of sensitivity of flow parameters differ from catchment to catchment, the curve number (CN2) has been found the most sensitive parameters in all gauged catchments. To facilitate the transfer of data from gauged catchments to ungauged catchments, clustering of hydrologic response units (HRUs) were done based on physical similarity measured between gauged and ungauged catchment attributes. From SWAT land use/ soil use/slope reclassification of LTB, a total of 142 HRUs were identified and these HRUs are clustered in to 39 similar hydrologic groups. In order to transfer the optimized model parameters from gauged to ungauged catchments based on these clustered hydrologic groups, this study evaluates three parameter transfer schemes: parameters transfer based on homogeneous regions (PT-I), parameter transfer based on global averaging (PT-II), and parameter transfer by considering Gilgel Abay catchment as a representative catchment (PT-III) since its model performance values are better than the other three gauged catchments. The performance of these parameter transfer approach was evaluated based on values of Nash-Sutcliffe efficiency (NSE) and coefficient of determination (R2). The computed NSE values was found to be 0.71, 0.58, and 0.31 for PT-I, PT-II and PT-III respectively and the computed R2 values was found to be 0.93, 0.82, and 0.95 for PT-I, PT-II, and PT-III respectively. Based on the performance evaluation criteria, PT-I were selected for modelling ungauged catchments by transferring optimized model parameters from gauged catchment. From the model result, yearly average stream flow for all homogeneous regions was found 29.54 m3/s, 112.92 m3/s, and 130.10 m3/s for time period (1989 - 2005) for region-I, region-II, and region-III respectively.

• 공업화학
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• 제19권1호
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• pp.98-104
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• 2008

본 연구는 광미오염토양을 대상으로 입자크기에 따른 토양세척기술의 중금속 추출특성 평가와 토양세척 전과 후의 화학적 분포형태를 파악하고자 실시되었다. 오염토양의 입자크기 별 총 농도는 모든 중금속에서 입자가 작을수록 증가하는 경향을 보였지만, Fe과 Mn은 입자크기와는 무관하였다. 0.05 M EDTA를 이용한 토양세척(Soil washing)에 의한 중금속 추출은 모든 중금속에서 추출 6 h 내에 준평형상태에 도달하였다. 추출효율은 입자크기가 작을수록 Pb, Cu, Zn의 일부에서 추출효율이 감소하였지만, Cd에서는 추출효율의 차이가 크지 않았다. Cd의 추출효율이 86~91%로 가장 높은 반면에 Fe이 5~14%로 가장 적었다. 화학적 분포형태는 토양세척 이전 모든 중금속에서 거의 대부분이 환원성, 산화성, 잔류성으로 존재하였으며 특히, Pb과 Cu는 입자가 작을수록 잔류성 형태도 증가하였다. 그러나, 0.05 M EDTA에 의한 토양세척 이후에는 Cu를 제외하고 Pb, Zn, Cd에서 상당부분이 환원성(Fe/Mn산화물)과 잔류성으로 존재하였고, Cu는 주로 산화성과 잔류성으로 존재하였다. 특히, Pb과 Cu는 입자가 작을수록 잔류성 형태도 증가하였다. 또한, Pb, Zn, Cd에서 환원성형태의 화합물이 0.05 M EDTA에 의해 거의 90% 이상이 제거되었다. 본 연구결과 광미오염토양의 중금속 분포형태 및 추출효율은 많은 인자들 외에 광물학적 요인과 함께 토양입자크기에 좌우되는 주요인자임이 확인되었다.

• 한국작물학회지
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• 제50권4호
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• pp.221-237
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• 2005

For developing the site-specific fertilizer management strategies of crop, it is essential to know the spatial variability of soil factors and to assess their influence on the variability of crop growth and yield. In 2002 and 2003 cropping seasons within-field spatial variability of rice growth and yield was examined in relation to spatial variation of soil properties in the· two paddy fields having each area of ca. $6,600m^2$ in Suwon, Korea. The fields were managed without fertilizer or with uniform application of N, P, and K fertilizer under direct-seeded and transplanted rice. Stable soil properties such as content of clay (Clay), total nitrogen (TN), organic mater (OM), silica (Si), cation exchange capacity (CEC), and rice growth and yield were measured in each grid of $10\times10m$. The two fields showed quite similar spatial variation in soil properties, showing the smallest coefficient of variation (CV) in Clay $(7.6\%)$ and the largest in Si $(21.4\%)$. The CV of plant growth parameters measured at panicle initiation (PIS) and heading stage (HD) ranged from 6 to $38\%$, and that of rice yield ranged from 11 to $21\%$. CEC, OM, TN, and available Si showed significant correlations with rice growth and yield. Multiple linear regression model with stepwise procedure selected independent variables of N fertilizer level, climate condition and soil properties, explaining as much as $76\%$ of yield variability, of which $21.6\%$ is ascribed to soil properties. Among the soil properties, the most important soil factors causing yield spatial variability was OM, followed by Si, TN, and CEC. Boundary line response of rice yield to soil properties was represented well by Mitcherich equation (negative exponential equation) that was used to quantify the influence of soil properties on rice yield, and then the Law of the Minimum was used to identify the soil limiting factor for each grid. This boundary line approach using five stable soil properties as limiting factor explained an average of about $50\%$ of the spatial yield variability. Although the determination coefficient was not very high, an advantage of the method was that it identified clearly which soil parameter was yield limiting factor and where it was distributed in the field.

• 한국토양비료학회지
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• 제47권6호
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• pp.586-593
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• 2014

Newly reclaimed tidal land is known to be in low status of soil fertility. The incorporation of crop residue is an effective method to improve soil properties and fertility in reclaimed saline soils. The objective of this study was to evaluate the efficiency of rice straw (RS) application to improve physico-chemical properties of saline-sodic soil and its contribution to productivity of whole crop barley. Increasing rate of rice straw improved growth parameter related to yield of whole crop barley, which increased tiller number significantly (p<0.05).The yield increased by 15% (F.W) and 9% (D.W) in rice straw-amended plots. The content of soil organic matter (SOM) in the surface soil (0-20cm) with rice straw incorporation increased by 5~9% (RS 2.5~RS 7.5) compared to RS 0, in which the content of SOM decreased after two consecutive cultivations. Rice straw incorporation promoted soil physico-chemical properties and nutrient-availability of the test crop, as indicated in change in soil bulk density, porosity and increased nutrient uptake of plant. Especially, the P content and uptake of whole crop barley increased with increasing the rate of rice straw application. In conclusion, the rice straw application at rates of $5.0-7.5ton{\cdot}ha^{-1}$ in reclaimed saline soils effectively improved soil properties and crop productivity, which has potentials to reduce the loss of chemical fertilizers and facilitate the favorable condition for crop growth under adverse soil condition.

• 한국산림과학회지
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• 제112권3호
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• pp.340-351
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• 2023

산사태는 매년 막대한 재산 피해와 인명 피해를 유발하는 주요 자연재해 중 하나이며, 기후변화의 영향으로 산사태 취약성은 더욱 증대되고 있다. 사면안정해석을 위한 다양한 매개변수 중 토심은 산사태 및 토석류 분석 시 주요 매개변수이며, 사면 안정성에 영향을 미치는 유역의 수문학적 과정을 평가하는 데 중요한 역할을 한다. 토심을 추정하는 정확한 방법은 현장에서 직접 지층을 조사하는 것이다. 하지만 이를 위해서는 많은 시간과 비용이 요구되므로 다양한 토심 예측 모델들이 제안되었으나 실용성 및 정확성 측면에서 다양한 한계가 존재한다. 본 연구에서는 산지사면에 대한 토심을 추정 하기 위하여 국내 산지를 대상으로 수행된 71개의 탄성파 탐사 결과를 수집하였으며 탄성파 속도 700 m/s를 기준으로 토심을 추정하였다. 이에 따라 사면의 경사, 고도, 토심 자료를 구축하고 토심에 대한 통계적 특성을 파악하였으며 경사와 토심 및 고도와 토심 간 상관관계를 규명하였다. 또한, 사면경사를 기반으로 한 다양한 토심 예측 모델을 조사하고 이에 대한 비교·분석을 수행하였으며 경사를 활용한 보정된 토심 예측식을 제안하였다.