Development of Model of Moisture Content Changing in Unsaturated Layered Soil Due to Non-Uniform Rainfall for Landslide Warning

Abstract

Landslide is behavior of soil moisture content on slope area changing due to rainfall infiltration. Increasing moisture content affect reduce soil shear strength which is cause of slope failure. Causal factors of soil moisture changing consist of rainfall intensity and soil properties including soil layers. Cause of soil on natural slope is residual soil that degree of weathering is not uniformly throughout soil depth, soil permeability in each layer are differ from other layer affect to soil moisture changing and perch water table occurring. This research object to create rain infiltration through multi-layer soil which difference soil properties for dynamic landslide hazard mapping, include landslide warning criteria setting. In this research, behavior of one dimension rain infiltration through two layered soil was studied. Two layers soil column which lower hydraulic conductivity material was placed in bottom layer was constructed for this purpose. The result can be shown that perched water table appeared at the depth above bottom layer. This behavior was including in mathematic model for spatial analysis of moisture content changing. . Layered soil Infiltration model in this research was create based on Green and Ampt (1911) model and modified for multi-layer soil. Landslide hazard assessment was calculated from safety of factor. After moisture content analysis on Tambon Maepoon and mountainous area of Patong Bay, which are study areas, by using rainfall data in landslide event found that the model able to work. And the result of safety factor can be used to assign landslide hazard level then set warning criteria.