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This study focuses on topographic hollows, their flow direction and flow accumulation characteristics, and highlights discharge of hillslope seepage so as to understand porewater pressure development phenomena in relation with slope failure in topographic hollows
. For this purpose, a small catchment in Niihama city of Shikoku Island in western Japan, with a record of seven slope failures triggered by typhoon-caused heavy rainfall on 19?20 October 2004, was selected. After extensive fieldwork and computation of hydro-mechanical parameters in unsaturated and saturated conditions through a series of laboratory experiments, seepage and slope stability modellings of these slope failures were done in GeoStudio environment using the precipitation data of 19?20 October 2004. The results of seepage modelling showed that the porewater pressure was rapid transient in silty sand, and the maximum porewater pressure measured in an area close to the base of topographic hollows was found to be higher with bigger topographic hollows. Furthermore, a threshold relationship between the topographic hollow area and maximum porewater pressure in this study indicates that a topographic hollow of 1000 sq. m area can develop maximum porewater pressure of 1.253 kPa. However, the porewater pressures required to initiate slope instability in the upper part of the topographic hollows is relatively smaller than those in the lower part of the topographic hollows
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In the Himalaya, people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster
. The intense summer monsoons are the main factor in triggering landslides. However, the relations between landslides and slope hydrology have not been a focal topic in Himalayan landslide research. This paper deals with the contributing parameters for the rainfall-triggered landslides which occurred during an extreme monsoon rainfall event on 23 July 2002, in the south-western hills of Kathmandu valley, in the Lesser Himalaya, Nepal. Parameters such as bedrock geology, geomorphology, geotechnical properties of soil, and clay mineralogy are described in this paper. Landslide modeling was performed in SEEP/W and SLOPE/W to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence. Soil characteristics, low angle of internal friction of fines in soil, medium range of soil permeability, presence of clay minerals in soil, bedrock hydrogeology, and human intervention were found to be the main contributing parameters for slope failures in the region
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A massive landslide in the Jure village of Sindhupalchowk District, Nepal, occurred on August 2, 2014, wiping out dozens of houses and blocking the Sunkoshi River
. The spectral element method (SEM) is employed here to study the stability of the slope where the landslide occurred, considering dry and wet slope conditions and pseudo-static seismic loading (with refer to 7.8Mw 2015 Barpak-Gorkha, Nepal earthquake). The results show that the Jure landslide slope becomes unsafe when the ground water table (GWT) is at the surface and peak ground acceleration (PGA) is greater than 0.2 g considering two slope cross-sections (section 2-2 and 3-3), and greater than 0.1 g for one slope cross-section (section 1-1). Based on the computational results, a correlation is made between the factor of safety (FS) and the PGA for the Jure landslide slope. Mitigation methods such as slope modification and ground water table reduction (drainage) are then proposed to increase the slope FS. The SEM results are then verified with a finite element method (FEM) technique. © 2018 American Society of Civil Engineers
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