Technical Studies

As a result of the geological weakness in Taiwan, the landslides often occur during heavy rainfall. Consequences of landslides can cause serious silting in reservoirs, mud or debris flow to destroy building and facilities, and therefore escalate economic losses. Assessment on landslide potential in the watershed by heavy rainfalls has been successfully analyzed by several physical and numerical studies. However, phenomena on landslides induced by the pressure in unsaturated porous media or the impact of rainfall-runoff process have not yet been appropriately explored. This study is to establish a two-dimensional, high-resolution model focused on rainfall-triggered unsaturated landslide in limited region with consideration on rainfall infiltration, surface runoff, and the variation of pore pressure in both saturated and unsaturated soil.

The model proposed several sub-models, including overland flow, saturated and unsaturated infiltration and landslides. The overland flow model is established based on the one-dimension kinematic equation. The saturated and unsaturated infiltration groundwater flow can be simulated by solving two dimension Richards’ equation, and the landslide potential will be analyzed by Bishop slope analysis method. After the influence of parameters and rainfall characteristics are examined, the developed model is then verified by in-situ testing data. Furthermore the developed model is used to examine the influence of rain pattern, then simulate the landslide potential under the conditions with various accumulated rainfall. And even the model is applied to Shihmen reservoir watershed to assess the influence of slope improvement measures. By following the assessment results, one can properly justify whether the structure or non-structure measures should be undertaken.