The behaviors of the electrical resistance at room and high (200°C) temperatures of acceptor (Mg)-doped BaTiO3 ceramics with the increase of acceptor concentration were investigated. A series of coarse-grained specimens with different acceptor concentrations that were sintered at various oxygen partial pressures was prepared. The critical acceptor concentrations, beyond which the room temperature resistance increases abruptly, were experimentally evaluated and they were found to increase with a decrease in oxygen partial pressure during sintering. Each defect and electron concentrations at sintering and room temperature as a function of acceptor concentration were theoretically calculated. The results calculated could explain the experimentally observed behavior of the resistance versus acceptor concentration. The high (200°C) temperature resistances under high electric field showed resistance degradation critically depending on acceptor concentration in the very small concentration range below ∼0.1mol%, which occurred easily with the increase of acceptor concentration. It was explained that such behavior was caused by the variation of potential barrier of grain boundaries for the migration of oxygen vacancies as a function of acceptor concentration.
Landslides are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration. This paper reports rainfall-induced landslides in partially saturated soil slopes through a field study. A comprehensive case study on the 2011 Umyeonsan (Mt.) landslides was highlighted. The incident involves the collapse of unsaturated soil slopes under extreme-rainfall event. A fundamental study was carried out on the cause and mechanism of landslide. A number of technical findings are of interest, including the failure mechanism of a depth of soil and effect of groundwater flow; the downward velocity of wetting front and the upward velocity of groundwater level. Based on this, an integrated analysis methodology for a rainfall-induced landslide is proposed in this paper that incorporates the field matric suction for obtaining hydraulic parameters of unsaturated soil. The field matric suction is shown to govern the rate of change in the water infiltration for the landslide analysis with respect to an antecedent rainfall. Special attention was given to a one-dimensional infiltration model to determine the wetting band depth in the absence of the field matric suction. The results indicate that landslide activities were primarily dependent on rainfall infiltration, soil properties, slope geometries, vegetations, and groundwater table positions. The proposed methodology has clearly demonstrated both shallow and deep-seated landslides, and shows good agreement with the results of landslide investigations.
IntroductionRainfall-induced landslides are common mass-movement processes in mountainous areas, particularly in areas covered by shallow soil deposit of different grading and origin. (Jeong et al., 2008;Cascini et al., 2010;Kim et al., 2017). Significant examples are frequently recorded in pyroclastic deposits in Central America (Capra et al., 2003) and New Zealand (Ekanayake and Philipps, 2002), in-situ weathered soils in Hong Kong (Take et al., 2004) and Japan (Wang et al. 2002), colluvial weathered deposits in Hong Kong Korea (Park et al, 2013). In particular, landslides of the flow-type (Hunger et al., 2001) represents a significant threat to lives, livelihoods and infrastructure in most mountainous areas. For example, when South Korea experienced record rainfall in June and July 2011, some 151 landslides occurred in the Umyeonsan Mt. region affecting 13 villages. These landslides significantly impacted society because the mountain is located in a central part of Seoul, South Korea.
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