Young-Suk Song

Geometrical and geotechnical characteristics of landslides in Korea under various geological conditions

The goal of this study is to determine the geometrical and geotechnical characteristics of landslides under various geological conditions using detailed field surveys, laboratory soil tests and precipitation records. Three study areas are selected to consider different rocks, including gneiss in Jangheung, granite in Sangju and sedimentary rocks in Pohang, South Korea. Many landslides have occurred in these three areas during the rainy season. Precipitation records indicate that landslides occurring in the gneiss area of Jangheung and granite area of Sangju may be influenced by the hourly rainfall intensity rather than cumulative rainfall. However, landslides occurring in the sedimentary rock area of Pohang may be influenced by hourly rainfall intensity and cumulative rainfall. To investigate the factors that influence these types of landslides, a detailed landslide survey was performed and a series of laboratory soil tests were conducted. According to the detailed field survey, most landslides occurred on the flanks of mountain slopes, and the slope inclination where they occurred mostly ranged from 26 to 30 degrees, regardless of the geological conditions. The landslide in the gneiss area of Jangheung is larger than the landslides in the granite area of Sangju and sedimentary rock area of Pohang. Particularly, the landslide in the sedimentary rock area is shorter and shallower than the landslides in the gneiss and granite areas. Thus, the shape and size of the landslide are clearly related to the geological conditions. According to the integrated soil property and landslide occurrence analyses results, the average dry unit weight of the soils from the landslide sites is smaller than that of the soils obtained from the nonlandslide site. The average coefficient of permeability of soils obtained from the landslide sites is greater than that of soils obtained from the non-landslide sites with the same geology. These results indicate that the soils from the landslide sites are more poorly graded or looser than the soils from the non-landslide sites.

Geotechnical Properties of Landslide Sites in Korea with Differing Geology

The goal of this study is to find out the relationship between geotechnical properties and landslide occurrence in areas with differing geology in Korea. The soil properties were measured in three study areas (Jangheung, Sangju and Pohang) which are underlain by gneiss, granite and sedimentary rock, respectively. Many landslides occurred in these areas during the rainy season. To investigate the factors that influence the landslides, a landslide survey was made, and a series of laboratory soil tests were carried out. The results of soil tests show that the average porosity of the soils originated from the gneiss of Jangheung and the granite of Sangju is greater than that of soils originated from the sedimentary rocks of Pohang. The average coefficient of permeability of the soils originating from the granite of Sangju is higher than that of soils from the gneiss of Jangheung and the sedimentary rocks of Pohang. The average coefficient of permeability of soils obtained from the landslide sites is greater than that of soils obtained from landslide-free sites in the same geology. The average shear strengths of soils obtained from the landslide sites are smaller than those of soils obtained from the landslide-free sites. It is confirmed that soils with low shear strength and high permeability are especially vulnerable to landslide occurrence.

Behavior of Vertical Pressure Imposed on the Bottom of a Trench

A series of model tests were performed to investigate the behavior of vertical pressure imposed on the bottom of a trench. The tests were conducted in two phases to generate soil arching due to soil deformation: (1) the backfilling phase and (2) the lowering-bottom phase. First, the backfilling phase was performed by filling sand into the trench, in which soil deformation was developed due to selfcompaction by the weight of the sand. The lowering-bottom phase was then conducted by lowering the bottom plate of the trench to induce additional soil deformation. The behavior of the vertical pressure acting on the bottom of the trench during the backfilling phase can simulate that of the vertical pressure imposed on the bottom of buried rigid pipes. The behaviors of buried flexible pipes could be observed during the lowering-bottom phase, in which both the minimum and the maximum vertical pressures could be obtained according to the induced soil deformation. A novel method for predicting the vertical pressures in each phase was proposed. The agreements between the predictions by the proposed method and the experimental results were demonstrated.

Monitoring and Stability Analysis of a Coal Mine Waste Heap Slope in Korea

This study investigated the deformation of the coal waste heap slope and the natural slope under the waste heap at Dogye village in Samcheock city, Korea. The deformation at the crest of the waste heap slope increased and then converged due to the temporal effect of the infiltration of rain into the ground after rainfall. The safety factor of the natural slope before the discharge of the waste was 2.14, and the safety factor of the waste heap slope, including the natural slope in the dry season was 1.66 and the safety factor in the rainy season was 0.98. According to the results of the monitoring and of the analysis, the slope movement initiated at the crest of the waste heap and the shape of slope failure seemed to be a circular sliding plane. The waste heap slope and the natural slope under the waste heap have experienced deformation due to the increasing self-load of the waste heap caused by rainfall infiltration.

Analyses on variations in the unsaturated characteristics of a mine waste-dump slope during rainfall

Field measurement units and a system were constructed and installed in a waste-dump slope at the Imgi mine to investigate and analyze the variations in the unsaturated characteristics of the soil. The field instrumentation system was composed of a data acquisition system, a solar system, and measuring sensors. The rainfall, matric suction, and volumetric water contents were continuously measured from the units in the instrumented site and analyzed with the soil water characteristic curve (SWCC) estimated from laboratory experiments. The variations in matric suction and volumetric water content were primarily affected by the rainfall intensity. At the surface of the slope, the largest increase and decrease in the changes in matric suction and volumetric water content were observed during the wetting and drying processes, respectively. The matric suction and volumetric water content measured from the instrumented area were compared with the SWCCs obtained from the laboratory test, and the measured data were located between the drying and wetting paths. The drying and wetting paths obtained from the laboratory test are regarded as primary drying and wetting curves, respectively. Therefore, the measured data can be defined as scanning curves, which are located between primary drying and wetting curves. The variations in matric suction according to volumetric water content were dependent on depth, and a wide range of variations was observed at shallow depths. It was confirmed that the unsaturated soil near the ground surface has the sensitive reaction induced by the infiltration and evaporation in nature.

Characteristics of the Cut Slopes located in Mt. Jang Area, Busan

The information of cut slope in Mt. Jang area, Busan is investigated in order to construct the Slope Management System in Urban Area. The slope inspection sheet is made to record the characteristics for cut slopes, and that is capable to be inputted slope information systematically. The cut slopes in Mt. Jang area are consisting of 69 slopes. Most of the cut slopes are constructed in cutting slope and retaining wall (CR). The cut slopes located in housing facilities are 46 slopes, and the slopes located in school facilities are 12 slopes. The traverse of cut slopes is mainly ranged from 50 m to 150 m, and the height is mainly ranged from 10 m to 20 m. The slopes combined with soil and rock are mostly distributed. The retaining wall was installed in the toe part of cut slope in order to increase the slope stability, and the additional reinforcement methods including the anchor, drainage, preventing rock fall, shotcrete and vegetation were installed at the toe part of cut slopes.