Landslide Evolution and Analysis of Failure Mechanism in LanTai Area

Due to slope land in Taiwan accounting for more than 70% of the region, the slope land often suffers typhoons and earthquakes induced landslides. For example, Typhoon Sinlaku caused the Lusan landslide in 2008, and landslides in Kaoping River Basin during Typhoon Morakot in 2009. Both caused severe damage, thus the potential and evolutions of large landslide become very important research topics. The Yilan Special Route No.1 is the main road between Yilan City and Taipin Mountain Forest Recreation Area. According to previous study, the road pavement and retaining walls both went through many rounds of repairement, especially in Lantai area. In the field investigation, we could observe that there were many cracks on the road and trees inclined toward the dowm slope direction. In this research, multi-stage aerial photos and the satellite images to determine landslide crown, and the results from field investigation were used to decide the potential scar and identified the failure criteria. The Particle Image Velocimetry (PIV) analysis was conducted for the terrain evolution in Lantai area, and results were referred to geological investigations and sampled the specimens from borehole cores, to determine the statue of ground formation and the laboratory tests were conducted. After transferring the point data from PIV analysis using ArcGIS and rosette statistics, the potential landslide area and the main sliding direction can be decided. Based on these results and borehole inclinometer results and drill reports, the model of potential landslide area could be established. This study combined the model with rainfall monitoring data in the field to back analyze the failure surface in each cases. The results showed that by using multi-stage images we could observe the potential landslide scar’s position, range, main sliding direction and the evolution of landslide in each cases. The scar location matched the failure surface location well. Key: Lantai area, Large-scale landslide, PIV analysis, Evolution of landslide, Stability of slope