Monitoring of the Evolution of a Deep-Seated Landslide in Lushan Area, Taiwan

The Lushan landslide area is located in Central Taiwan and has been famous as a hot spring recreation area. The elevation of the major slope ranges from 1,080 to 1,450 m. The first significant displacement was documented in 1994 caused by Typhoon Doug. However, the records of slope displacement start much earlier according to the local residents, and repairs of the Tai-14 Highway are frequently conducted. The geological formation in Lushan Area is majorly slate interlayered with thin layers of metamorphic sandstone. The landslide scars identified from the aerial photos suggested a large-scale landslide along with several smaller landslide scars inside the major scar. In this study, the landslide monitoring is mainly conducted using LiDAR and close range photogrammetry since early 2007. In September 2007, Typhoon Sinlaku struck the Central Taiwan and significant movement of Lushan landslide was detected. The monitoring results were cross-examined and analyzed to identify displacement conditions of the slope with the corresponding rainfall and ground water table. The monitored results and failure mechanism analysis suggested that a deeper sliding surface developed at a depth of 108 m in 2007 during Typhoon Sinlaku, and the monitoring data provided information on landslide evolution and displacement conditions of both the deep-seated landslide and local small-scale landslides.