Assessment of Landslide Recurrence by Onsite Monitoring - Incidence of Hung-yeh Landslide -

Chia-Chun WU, Pei-Hsi WANG, Chih-Hui WANG, Ching-Yen CHANG and Te-Ling WU

Typhoon Meranti invaded Taiwan from Sept. 12 through 16 in 2016 and brought 633 mm of rain in 48 hours. A large-scale landslide behind Hong-Yeh Village of Taitung County consequently occurred on Sept. 15, which produced 40,000 m3 of debris. Debris that affecting local settlement and blocking the bridge clearance was dredged. Countermeasure structures were immediately designed and implemented. Locations for permanent resettlement were evaluated. Nevertheless, uncertainty of landslide recurrence and feasibility of the countermeasures in coping with future disaster either caused by landslide or debris flow has troubled the government agencies. Hence, field geological survey, outcrop assessment, micro-terrain interpretation, core samples from core drills, Electrical Resistivity Image Profiling, and inclination as well as water stage readings from five boreholes were used to assess the likelihood of landslide recurrence. All evidence gathered onsite suggested the recurrence of landslide is highly possible. The unstable mass situated on upper landslide site displaced another 6.5 m eastward along the slope after a 5-day 924-mm torrential storm with peak one-day rainfall of 407 mm. Numerical simulations at different storm return periods with countermeasure designs scenarios were conducted to ensure the safety of Hong-Yeh Village and the functionality of countermeasure structures from debris-flow disaster. Adjustments on structure design were made accordingly and were implemented onsite, which helped reduce the areas of risk scope by 40.1%.

2018/1 15-23