Geotechnics for Natural Disaster Mitigation and Management by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9789811388286
Publisher: Springer Singapore

7.2 Rainfall-Induced Landslides

The impact of rainwater infiltration in causing landslides is widely recognized. Hydrological activity imposes a significant impact on the stability of a slope, whereas modification of slope topography and type of land use has a significant impact on the hydrology of the hillslope [26]. The presence of capillary pressure in unsaturated soils can have a big impact on the stability of a slope. Capillary forces hold fine particles of soil together, and can provide an additional cohesive component to the soil [9]. This apparent cohesion can give an apparent sense of safety. The magnitude of the capillary force holding the soil particles together starts decreasing as the soil saturation starts to increase [1, 5]. Rainfall infiltration results in the increase of water content and decrease in the matric suction, thereby raising the unit weight and reducing the shear strength of soil within the colluvium of the landslide. The rate of infiltration would also depend on the type of landuse, or more specifically, the surface cover, inclination of the soil surface, the intensity and duration of the rainfall, the hydraulic conductivity and degree of saturation of the soil [2, 17]. Presence of hydrologic boundaries further worsens the situation, whereby pore pressure build up will occur due to difference in hydraulic conductivity, and thereby reduce the shear strength that can be mobilized and cause an increase in seepage pressure [30]. Therefore, for landslide susceptibility analysis of hillslopes in the city of Guwahati, determination of infiltration capacity, hydraulic conductivity and the characterization of the soil strength behaviour under different wetting and seepage conditions forms the first and foremost steps. Hillslopes within the city of Guwahati consist of residual soils in unsaturated condition, which renders the conventional soil mechanics approach of assessing the stability of these slopes to be inadequate. To assess the potential susceptibility to rainfall-induced landslide, an effective modelling of the changes in water content and matric suction, in response to rainfall infiltration, is essential.

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