• Journal of the Korean Geotechnical Society
• /
• v.15 no.5
• /
• pp.125-139
• /
• 1999

It is difficult to evaluate the shear strength of weathered residual soils because of the difficulties of undisturbed sampling. In this study, a sampling device, direct shear box with shoe, was developed in order to get undisturbed samples easily for direct shear tests, and undisturbed samples could be successfully obtained. Through direct shear tests on undisturbed samples, the shear strength was evaluated with the variation of saturated conditions. In order to consider the effect of disturbance on the shear strength, a static compaction device was developed, and then it was found that undisturbed samples show greater shear strengths than the disturbed ones under natural water contents and similar strengths to the ones under soaked conditions. Further, the shear strength evaluated from direct shear tests was compared with the result of triaxial tests on undisturbed samples, and soaked strengths of the former were similar to the latter. As the result of stability analyses on an actual failed slope, it was found that the shear strength can be evaluated reasonably using direct shear box with shoe.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.03a
• /
• pp.12-19
• /
• 2006

Landslide model experiments considering hourly rainfall were performed to investigate and predict the run out distance induced by landslides. The model flume and the rainfall simulator were designed and produced. The model flume was designed in consideration of the landslide characteristics of Korea. The landslides in Korea were mainly occurred in the interface between soil layer and rock layer. The rainfall simulator was produced for controlling hourly rainfall ranged from 100mm/hr to 1,000mm/hr. Jumnunjin standard sand as slope soils was placed on the model flume. The model experiments were performed with changing the hourly rainfall ranged from 150mm/hr to 250mm/hr. In this experiments, the inclination of slope was 25o and the relative density of slope soils was 35%. As a result of experiments, the pore water pressure is rapidly increased at landslide occurring time, and the scale of landslide is increased with increasing in hourly rainfall. The spreading range of run out distance is occurred with pan type, and the spreading width and length are rapidly increased in its early stage and slowly increased after early stage. Also, The increasing velocity of run out distance of debris is influenced by hourly rainfall.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.2
• /
• pp.71-78
• /
• 2012

Rainfall infiltration test under one dimensional condition is conducted to evaluate the effect of rainfall intensity on seepage velocity and infiltration characteristics for initial unsaturated sediment. Experimental results are compared with those numerical simulations with respect to variations of pore water pressure, degree of saturation and discharge velocity with time, and both results give good agreement. High rainfall intensity tends to increase seepage velocity almost linearly. But it shows rapid increase as rainfall intensity approaches saturated hydraulic conductivity of the sediment. In addition, the upper part of wetting front depth is partially saturated, not fully. Therefore, actual wetting front depth is considered to advance faster than theoretical prediction, which leads to slope instability of unsaturated slope due to surface rainfall.

• Atmosphere
• /
• v.23 no.4
• /
• pp.539-547
• /
• 2013

The objective of this study is to standardize the calculation method of Palmer Drought Severity Index (PDSI) for the three Drought Management Agencies (DMA) in south Korea, and to evaluate the PDSI applicability. For comparison and review of the method, the code and input data of PDSI are collected from each DMA. The calculation method is the same, but the used input data (number of meteorological stations, normal year period, Available Water Capacity (AWC) of the soil) are different. Through discussions with drought experts and literature review, the standardized method is determined. 61 stations which have the data period more than 30 years are selected. Also the normal year is fixed for 30 years and updated every 10 years. The observed AWC is utilized using GIS data. Empirical equation of PDSI is re-estimated according to domestic climate characteristics. For evaluating the standardized PDSI, past drought events are investigated and drought indices including the existing SPI and PDSI are used for comparative analysis. As results, although the accuracy of standardized PDSI through ROC analysis is lower than SPI, the newly standardized PDSI is better than existing PDSI from DMA, Also it reasonably explain the spatial drought situation through the spatial analysis.

• Research in Plant Disease
• /
• v.14 no.2
• /
• pp.131-133
• /
• 2008

From 2006 to 2007, the stem rot of Elsholtzia splendens Nakai caused by Sclerotium rolfsii occurred sporadically in an herbs exhibition at Gyeongsangnam-do Agricultural Research and Extension Services, Korea. The typical symptom is water-soaking, dark brown on the stem and rotting, wilting and blighting. The infected plants were mostly died. White mycelial mats were spread over lesions, and then sclerotia were formed on stems and near soil line. The sclerotia were globoid in shape, $1{\sim}3$ mm in size and white to brown in color. The optimum temperature and sclerotia on PDA was $30^{\circ}C$ and the hyphal width was $4{\sim}9{\mu}$. The typical clamp connections were observed in the hyphae of the fungus grown on PDA. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report on the stem rot of E. splendens caused by S. rolfsii in Korea.

• Research in Plant Disease
• /
• v.17 no.2
• /
• pp.225-227
• /
• 2011

The stem rot of Chrysanthemum zawadskii var. latilobum occurred in the landscape field of Sanggwan-myeon, Wanju-gun, Jeonbuk, Korea in September 2009. The typical symptoms of the disease were water-soaking and dark brown rot on the stem, wilting and blighting. Most infected plants died of the disease. White mycelial mats were spread over lesions and brown sclerotia were formed on stems and near soil surface. The sclerotia were spherical or irregular, 0.8-3.5 (mean 1.8) mm in size on potato dextrose agar, brown in color. The optimal temperature range of hyphal growth was $25-30^{\circ}C$ and the hyphal diameter was 4-9 ${\mu}m$. Clamp connections were observed in the hyphae of the fungus grown on potato dextrose agar. Pathogenicity of the casual organism was provided on C. zawadskii according to Koch's postulate. The fungus was identified as Sclerotium rolfsii on the basis of mycologiclal characteristics and pathogenicity test to host plants. This is the first report on the stem rot of C. zawadskii caused by S. rolfsii in Korea.

• Research in Plant Disease
• /
• v.15 no.1
• /
• pp.51-53
• /
• 2009

The fruit rot of watermelon (Citrullus lanatus) occurred sporadically in the farmers field at Chojeondong, Jinju city, Korea, in 2007. The typical symptom was water-soaked, brown on the fruit, and than infected fruits were mostly rotted. White mycelial mats were spread over lesions, and then sclerotia were formed on fruit and near soil line. The sclerotia were globoid in shape, $1{\sim}3\;mm$ in size and white to brown in color. The optimum temperature for mycelial growth and sclerotia formation on PDA was $30^{\circ}C$ and the hyphal width was $4{\sim}8{\mu}m$. The typical clamp connections were observed in the hyphae of the fungus. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii. This is the first report on the fruit rot of watermelon by S. rolfsii in Korea.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.7
• /
• pp.45-55
• /
• 2004

In the past it has been often observed that the shear stresses at failure are much smaller than the shear strength obtained from traditional laboratory tests and conventional analysis technique is inadequate in stiff soil, such as cemented sand. Many researchers have brought attention to the fact that the presence of flaws i.e. fissures, cracks, joints have a great effect on the strength and overall stress-strain behavior of such materials. They have thought that fracture mechanics may appropriately be adopted as a good tool for analysis of these materials. However, the use of fracture mechanics concept especially for cemented sands is faced with difficulties in obtaining relevant parameters, because fracture parameters and predictions are highly dependent on the material constituents and the size of specimens as well as the size of particles. This paper addresses the effects of sizes which include specimen and aggregate on fracture properties of cemented sand. The results of laboratory tests show that the sizes of specimens and particle have a great effect on the fracture properties such as nominal strength of cemented sand.

• Journal of Korean Society of Forest Science
• /
• v.98 no.2
• /
• pp.156-162
• /
• 2009

Nebkhas are widely distributed in farming-pastoral zones, typical grassland and desert margins. In the southeast of the Inner Mongolia Plateau, it is mainly distributed at the leeward of cultivated land and alluvial fan, severe deterioration rangeland and around residential points. Through the field measurement and statistical analysis of Caragana microphylla Lam. Nebkhas morphological parameters (length, width and height of Nebkhas are included), the results show that there were close correlations between the Nebkhas morphological parameters. The ranges of height and width of Nebkhas changed dramatically and have reached up to 11.44 m and 7.97 m respectively, however, the change range of height was relatively smaller and just 1.09 m. The morphological parameters change of the same type Nebkhas in the same region was large ranging from 0.56 m in height, 3.56 m in width to 6.96 m in length, while the morphological characteristics of the same type Nebkhas in different regions were much similar. A correlation between length and width was significantly positive, but the correlations between height and length, and between height and width were much more complicated. It can be concluded that the Nebkhas in Zhengxiangbai Banner and Taipusi Banner were at the initially growing stage, while the Nebkhas in Huade County belonged to a transitional stage from the growing phase to the stabilizing phase. The changing regularity of distance between Nebkhas in along-wind direction was not consistent.

• KCID journal
• /
• v.13 no.2
• /
• pp.262-273
• /
• 2006

The Soil and Water Assessment Tool (SWAT) model has been widely used in hydrology and sediment simulation worldwide. In most cases, the SWAT model is first calibrated with adjustments in model parameters, and then the validation is performed. However, very little study regarding the effects on SWAT estimation of subwatershed delineation was performed. Thus, the SWAT model was applied to the Doam-dam watershed with various threshold values in subwatershed delineation in this study to examine the effects on the number of subwatershed delineated on SWAT estimation. It was found the flow effect of subwatershed delineation is negligible. However there were huge variations in SWAT estimated sediment, T-N, and T-P values with the use of various threshold value in watershed delineation. Sometimes these variations due to watershed delineation are beyond the effects of parameter adjustment in model calibration and validation. The SWAT is a semi-distributed modeling system, thus, the subwatershed characteristics are assumed to be the same for all Hydrologic Response Unit (HRU) within that subwatershed. This assumption leads to variations in the SWAT estimated sediment and nutrient output values. Therefore, it is strongly recommended the SWAT users need to use the HUR specific slope length and slope value in model runs, instead of using the slope and the corresponding slope length of the subawatershed to exclude the effects of the number of subwatershed delineated on the SWAT estimation.