Chang-Oh Choo

Effects of Rainfall Intensity, Soil Slope, and Geology on Soil Erosion in Korea

Extended Abstract In recent decades, there has been a growing concern over the soil erosion in Korea which is mostly induced by extreme rainfall during a rainy summer season. Soil erosion is partly associated with landslide or failures of slope where thick soil profile develops. The supply of fine particles to dams and rivers induced by soil erosion causes a critical turbidity composed of suspended matters over a long period. It was shown that landslides induced by debris flow in Korea are commonly related to the geotechnical properties and clay mineralogy of precursor soils developed on bedrock [1]. This study aims to elucidate the importance of geological characteristics, soil slope, and rainfall intensity in relation to soil erosion. The analytical results by XRD show that primary clay minerals contained in the slopes where intensive soil erosion takes place are illite, chlorite, kaolinite, and montmorillonite. It is evident that erosion rates were proportional to rainfall and clay contents. Because illite is the most abundant clay in soil, it serves as one of the most effective factors that induce intensive soil erosion. According to monitoring on field sites, the rates of soil erosion increased with increasing slope angles and precipitation rates. Soil erosion was initially controlled by rill development and original topography. The runoff amounts discharged from soil increased turbidity and clay contents removed, especially high in metamorphic rocks. This study demonstrated that it is possible to predict a critical depth and the change in the safety factors of a slope subject to rain infiltration and that a rainfall-induced landslide largely depends on clay mineralogy in the soil and slope parameters affecting soil erosion. Environmental management for soil erosion, especially landslide related to significant soil loss, needs systematic observations and monitoring on different lithologies at varying rates of outflow, which can be supported by understanding mechanical properties and clay mineralogy of soils at slopes.

A Study on Weathering Processes of Tafoni in Mt. Cheonsaeng, Gumi, the Republic of Korea: Interpretation of Water Content Data using GIS Interpolation Analysis

This study examines the processes of rock weathering and tafoni formation targeting tafoni at Mt. Cheonsaeng, Gumi-si, Gyeongsangbuk-do. In the study area, a frequency of tafoni is high in conglomerate and conglomeratic sandstone among regional sedimentary rocks, which means that an initial stage of the formation begins a breakaway of gravel from bedrock and also exfoliation from rock surface. Geomorphologically tafoni have intensively been developed at the southfacing slope with exposed rocks, which means that its formation was favorably controlled by environmental conditions including strong influences of mechanical weathering in winter and chemical weathering in summer times. The results of measuring water content at a tafoni-bearing rock surface using GIS interpolation analysis indicate that moisture rate in/around tafoni is higher than the periphery. Thus, it is considered that moisture distribution at a rock surface plays a role in its formation. Analysis of percipitation and secondary minerals induced by chemical weathering is in progress.

A Study on Improving Installation Guideline of Facilities to Protect Groundwater Contamination: Applications of Packer Grouting to Contaminated Wells

Because the present groundwater law broadly regulates a simple and impractical guideline ignoring aquifer characters and geology, general purpose facilities for protection of groundwater contamination is still considered unsatisfactory to ensure groundwater resources. In recent, there have been growing attempts in the packer development as crucial techniques and devices for groundwater protection. This study investigated the application of packer grouting techniques to contaminated groundwaters of two well sites in the Andong and Yeongi areas, both of which revealed a satisfactory effect with improved water quality: 94% decrease in turbidity at the Andong area and 60% decrease in -N, respectively. Based on aquifer characters including geology, weathering depth, fracture pattern, hydraulic gradient, and the flow path of contaminants, the integrated properties of groundwater contamination should be evaluated and treated with the help of accurate analyses such as bore hole imaging and monitoring data. Packer grouting and casing on well to ensure the useful aquifer free of contaminant are expected to play important role in inhibiting the inflow of contaminants when adequately applied. Therefore it is concluded that these can serve as reliable tools in remediation and protection of contaminated groundwater as well as efficient utilization of groundwater.