• Journal of Soil and Groundwater Environment
• /
• v.21 no.6
• /
• pp.36-45
• /
• 2016

Variability in precipitation due to climate change causes difficulties in securing stable surface water resource, which requires understanding of relation between precipitation and stream discharge. This study simulated stream discharge in a small mountainous forested catchment using antecedent precipitation index (API) models which represent variability of saturation conditions of soil layers depending on rainfall events. During 13 months from May 2015 to May 2016, stream discharge and rainfall were measured at the outlet and in the central part of the watershed, respectively. Several API models with average recession coefficients were applied to predict stream discharge using measured rainfall, which resulted in the best reflection time for API model was 1 day in terms of predictability of stream discharge. This indicates that soil water in riparian zones has fast response to rainfall events and its storage is relatively small. The model can be improved by employing seasonal recession coefficients which can consider seasonal fluctuation of hydrological parameters. These results showed API models can be useful to evaluate variability of streamflow in ungauged small forested watersheds in that stream discharge can be simulated using only rainfall data.

• Geomechanics and Engineering
• /
• v.23 no.4
• /
• pp.339-349
• /
• 2020

This study investigates the feasibility of using the results of the UPV (ultrasonic pulse velocity) test to assess the UCS (unconfined compressive strength) of unsaturated soil. A series of laboratory tests was conducted on samples of unsaturated lateritic soils of northern Taiwan. Specifically, the unconfined compressive test was combined with the pressure plate test to obtain the unconfined compressive strength and its matric suction (s) of the samples. Soil samples were first compacted at the designated water content and subsequently subjected to the wetting process for saturation and the following drying process to its target suction using the apparatus developed by the authors. The correlations among the UCS, s and UPV were studied. The test results show that both the UCS and UPV significantly increased with the matric suction regardless of the initial compaction condition, but neither the UCS nor UPV obviously varied when the matric suction was less than the air-entry value. In addition, the UCS approximately linearly increased with increasing UPV. According to the investigation of the test results, simplified methods to estimate the UCS using the UPV or matric suction were established. Furthermore, an empirical formula of the matric suction calculated from the UPV was proposed. From the comparison between the predicted values and the test results, the MAPE values of UCS were 4.52-9.98% and were less than 10%, and the MAPE value of matric suction was 17.3% and in the range of 10-20%. Thus, the established formulas have good forecasting accuracy and may be applied to the stability analysis of the unsaturated soil slope. However, further study is warranted for validation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.1
• /
• pp.21-26
• /
• 2013

In recent study, infiltration analysis considering rainfall intensity is more economical and practical than existing analysis method. Revised construction slope design standard is also stated to full-fill infiltration analysis considering rainfall for practical stability review. Infiltration analysis considering rainfall for practical stability review. But, to infiltration analysis, the process is complicated by ground impermeability and rainfall intensity. In this study, we perform infiltration analysis to charge infiltration conditions, soil type and rainfall characteristics, for more pratical stability review. Using the result, we can suggest construable condition on the assumption that soil is saturated up to surface zone.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.14
• /
• pp.71-77
• /
• 1973

To observe the effect of fused phosphate fertilization, as a soil improvement material, in low productive paddy field which has rapid permeable sandy-skeletal texture, this experiment was carried out under five different levels of fused phosphate. The results obtained are briefly as follows: 1. Rice, grown in areas receiving annual fused phosphate application of from 200 to 250kg per 10a showed yield increases of about 10 to 27 percent based on 1, 000 grain weight of brown rice. Other favorable effects from high fused phosphate applications include increased number of panicles, faster ripening rate of the rice, and lower infection rate of blast. 2. In the soil analysis after the experiment, the useful soil chemical properties, such as available phosphate, silica, soil pH, exchangeable calcium, magnesium, and base saturation were increased significantly. The exchangeable potassium, however, was not changed noticeably. 3. The relation between the major soil chemical properties, especially available phophate and silica, and yield component which directly effect yields, showed a significant correlation statistically.

• Geomechanics and Engineering
• /
• v.39 no.3
• /
• pp.241-256
• /
• 2024

The shear strength (SS) of soil is a critical parameter utilized in the design of civil engineering projects. The SS parameters, including cohesion (c) and friction angle (𝜑), can be determined through methods conducted either in the field or within a laboratory environment. However, the traditional method for determining SS parameters are not only costly but also time-consuming. Recently, the application of machine learning (ML) in geotechnical problems has received increasing attention. In order to select an appropriate ML model and assess the effect of physical properties on the SS of soil. This research endeavors to predict critical SS parameters of soil through the application of five machine learning (ML) models, integrating easily-available physical soil index, including specific gravity (G), saturation degree (Sr), liquid limit (LL), silt content (SC), and clay content (CC). The used ML techniques include Extreme Gradient Boosting (XGBoost), Random Forest (RF), Multilayer Perceptron (MLP), Support Vector Machine (SVM), and Convolutional Neural Network (CNN). A range of metrics, encompassing the root mean square error (RMSE), mean absolute error (MAE), and determination coefficient (R²) were used to measure the predictive efficacy of the employed models as well as compare the performance of the used ML models. The values of R² range from 0.769 to 0.987 indicate that all ML models exhibit excellent predictive capabilities for estimating SS parameters, in which the XGBoost, and CNN techniques show outperforming results compared to the other models. The study uses decision tree feature importance (DTFI) and coefficient feature importance (CFI) techniques to investigate how various physical properties impact the predictive capabilities of the model and indicates that both G and LL have a substantial impact on the predictive accuracy of cohesion and friction angle.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2006.05a
• /
• pp.2-11
• /
• 2006

In the processes of hydrological cycle, when precipitation reaches the ground surface, water may become surface runoff or infiltrate into soil and then possibly further percolate into groundwater aquifer. A part of the water is returned to the atmosphere through evaporation and transpiration. Soil moisture dynamics driven climate fluctuations plays a key role in the simulation of water transfer among ground surface, unsaturated zone and aquifer. In this study, a one-layer canopy and a four-layer soil representation is used for a coupled soil-vegetation modeling scheme. A non-zero hydraulic diffusivity between the deepest soil layer modeled and groundwater table is used to couple the numerical equations of soil moisture and groundwater dynamics. Simulation of runoff generation is based on the mechanism of both infiltration excess overland flow and saturation overland flow nested in a numerical model of soil moisture dynamics. Thus, a comprehensive hydrological model integrating canopy, soil zone and aquifer has been developed to evaluate water resources in the plain region of Huaihe River basin in East China and simulate water transfer among precipitation, surface water, soil moisture and groundwater. The newly developed model is capable of calculating hydrological components of surface runoff, evapotranpiration from soil and aquifer, and groundwater recharge from precipitation and discharge into rivers. Regional parameterization is made by using two approaches. One is to determine most parameters representing specific physical values on the basis of characterization of soil properties in unsaturated zone and aquifer, and vegetations. The other is to calibrate the remaining few parameters on the basis of comparison between measured and simulated streamflow and groundwater tables. The integrated modeling system was successfully used in the Linhuanji catchment of Huaihe plain region. Study results demonstrate that (1) on the average 14.2% of precipitation becomes surface runoff and baseflow during a ten-year period from 1986 to 1995 and this figure fluctuates between only 3.0% in drought years of 1986, 1988, 1993 and 1994 to 24.0% in wet year of 1991; (2) groundwater directly deriving from precipitation recharge is about 15.0% t of the precipitation amount, and (3) about half of the groundwater recharge flows into rivers and loses through evaporation.

• Korean Journal of Soil Science and Fertilizer
• /
• v.47 no.4
• /
• pp.269-274
• /
• 2014

Series of field experiments were conducted to evaluate the long term effect of gypsum and crop residue on crop yield and soil health in rice-wheat crop rotation system in salt affected soil. A saline-sodic field having $EC_e$ (electrical conductivity of the saturation extract) 4.77 ($dSm^{-1}$); pH ($H_2O$) 8.96; SAR 43.78 ($mmol\;L^{-1}$) and gypsum requirement (G.R.) 2.86 (Mg $acre^{-1}$) was selected on Soil Salinity Research Institute Farm. Five treatments consisting of ($T_1$) control, ($T_2$) gypsum at 100% G.R., ($T_3$) gypsum at 25% G.R. + wheat straw at $3Mg\;ha^{-1}$, ($T_4$) gypsum at 25% G.R. + rice straw at $3Mg\;ha^{-1}$, ($T_5$) gypsum at 25% G.R.+ rice and wheat straw at $3Mg\;ha^{-1}$ were replicated four times under completely randomized block design. The data indicated that grain and straw yield of rice and wheat was significantly (P<0.05) increased by all the amendments used either single or in combination. $T_2$ (gypsum at 100% G.R.) significantly (P<0.05) increased grain and straw yield of rice and wheat crops followed by $T_3$ (gypsum at 25% G.R. + wheat straw at $3Mg\;ha^{-1}$) when compared with control. Soil properties were also improved by used amendments, pronounced decreased in $EC_e$, $pH_s$ and SAR were recorded in $T_2$ followed by $T_3$. The efficiency of the treatments could be arranged in following order gypsum at 100% G.R.> gypsum at 25% G.R. + wheat straw at $3Mg\;ha^{-1}$ > gypsum at 25% G.R. + rice and wheat straw at $3Mg\;ha^{-1}$ > gypsum at 25% G.R. + rice straw at $3Mg\;ha^{-1}$ > control.

• Korean Journal of Soil Science and Fertilizer
• /
• v.6 no.1
• /
• pp.1-8
• /
• 1973

This study examined the morphological, physical and chemical characteristics of the Yesan and the Songjeong series derived from residuum of the granite developed on gently sloping to rolling relief in Honam reclamable land Area. The results of this study are summarized as follows. 1. The morphological characteristics. In the Yesan series, the surface soils(Ap horizons) are brown to dark brown sandy loam. The subsoils(B horizons) are yellowish red to red sandy clay loam to sandy loam and the soil profile development is weak. The Songjeong series, the surface soils (Ap horizons) are washed by erosion, so the subsoils are revealed on the surface, and these are dark red silty clay loam. The subsoils (B horizons) are red silty clay loam and thin clay cutans are formed on the ped faces of the structure. The substrata of two soil series are deeply weathered granitic saprolite. 2. The physical and chemical characteristics. The distribution of clay content tends to increase from surfaces to subsoils with depth gradually. On the Yesan series, the content of clay is less than 18%, soil pH (6.0 in the surface-soil, 4.5-5.0 in the subsoil), the content of organic matter (1.8% in the surface soil, 0.1~0.4% in the subsoil), available phosphate (40 ppm), the cation exchange capacity(4~8 me/100 gr) are very low, and the base saturation (57.8% in the surface soil, 46.3% in the subsoil) is moderate. On the Songjeong series, the content of clay is 30~40%, pH (5.7-6.0), the content of in organic matter (1.25% in the surface soil, 0.1~0.4% in the subsoil), available phosphate(4 ppm), the cation exchange capacity(6.2 me/100 gr in the surface soil, 2~6 me/100gr in the subsoil) are very low, and the base saturation(28.1% in the surfacesoil, 16~23% in the subsoil) is also low. 3. The Yesan and Songjeong series are for med under a temperate humid climate, and classified as Red Yellow Soils in the old classification system. According to U.S.D.A. 7th approximation the former belongs to Typic Dystrochrepts in Inceptisols, and the latter, Typic Hapludults in Ultisols.

• Journal of Soil and Groundwater Environment
• /
• v.11 no.4
• /
• pp.48-56
• /
• 2006

Using a continuous injection tracer test at a multi-soil layer deposit, the difference of hydrodynamic dispersions in unsaturated and saturated zones were analyzed through breakthrough curves of Rhodamine WT, linear regression of concentration versus time, concentration variation rates versus time, and concentration ratio according to the distance from injection well. As a result of continuous injection tracer test, the difference of the maximum concentrations of Rhodamine WT in unsaturated and saturated zones were 13-15 times after 160 hours, and the increased rate of concentration versus time in unsaturated zone was about 10 times higher than in saturated zone. The fluctuation of Rhodamine WT breakthrough curve and concentration variation rate with time in saturated zone were larger than in unsaturated zone. Rhodamine WT concentration ratio with the distance from the injection well in saturation zone was linearly decreased faster than in unsaturated zone, and the elapsed time necessary for the concentration ratio less than 2 was longer in saturation zone. The differences resulted from the lower concentration and slower hydrodynamic dispersion of Rhodamine WT at the saturation zone of the multi-soil layer deposit, in which groundwater flow significantly flow and aquifer materials have high hydraulic heterogeneity. Effective porosity, longitudinal and transverse dispersivities were estimated $10.19{\sim}10.50%,\;0.80{\sim}1.98m$ and $0.02{\sim}0.04m$, respectively. The field longitudinal dispersivity is over 12 times larger than the laboratory longitudinal dispersivity by the scale-dependent effect.

• Journal of Korean Society of Forest Science
• /
• v.83 no.3
• /
• pp.380-390
• /
• 1994

This study was conducted to investigate the effects of the topographical factors (16 items), physico-chemical properties of soil (13 items) and meteorological factors(9 items) on the height growth of Pinus thunbergii stands along the coastal area in Korea. According to the coefficients by partial correlation analysis in total area, it was found that tree height growth was considerably affected by local topography, soil hardness, soil B-horizental depth, effective soil depth, soil moisture, parent rock, soil texture, and etc.. And the soil factors were available $P_2O_5$, total nitrogen, base saturation, exchangeable $Ca^{{+}+}$, and etc.. In partial correlation analysis, annual relative humidity, annual precipitation, index of aridity, and etc. were found to be the most important factors influencing on tree height growth of Pinus thunbergii stands. In conlusion, the topographical, soil and meteorological factors have multiplex influence on the tree height growth in the Pinus thunbergii stands. They promise to provide the basis of improving not only the selection of suitable sites and the management of soil fertilizer but also the estimation of growth and yield. Hence these results would be used successfully for the design in the scientific forest working plan.