Non-catastrophic Hongtsaiping Landslide Induced by the 1999 Chi-Chi Earthquake in Central Taiwan Insights from Distinct Element Method 1Chia-Han Tseng (曾佳漢) 1Jyr-Ching Hu, 1Chao-Lung Tang, 2Yu-Chang Chan, 3Ming-Lang Lin, 4Jin-Fa Lee, 4Jheng-Yue Wei 1Department of Geosciences, National Taiwan University, Taipei, Taiwan 2Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan 3Department of Civil Engineering, National Taiwan University, Taipei, Taiwan 4Central Geological Survey, Taipei, Taiwan
Introduction of the Hongtsaiping Landslide Background Results from various kinds of research Distinct Element Method (DEM) applied to the Hongtsaiping Landslide Reasons for use of the DEM Results of 2D and 3D
INTRODUCTION
Faulting
Faulting Faults all around Taiwan island, 42 active faults The Chi-Chi earthquake in 921 Red lines: active faults (modified from CGS, 2000)
Landslide areas ‧ 9,272 landslides greater than 625 m2, total area of 127.8 km2. ‧ellipse-shaped region, coinciding with the trend of regional faults Purple areas: landslides triggered by the 1999 Chi-Chi earthquake (Lee et al., 2000)
Landslide areas ‧ 9,272 landslides greater than 625 m2, total area of 127.8 km2. ‧ellipse-shaped region, coinciding with the trend of regional faults ‧Heavy rainfall due to typhoon events Purple areas: landslides triggered by the 1999 Chi-Chi earthquake Yellow areas: landslides (1999-2000) (Lee et al., 2000)
Jiufengershan 36 million m3 in volume
landslide triggered by the Chi-Chi earthquake Tsaoling • 120 million m3 in volume, the largest landslide triggered by the Chi-Chi earthquake
volume, non- catastrophic landslide reported after 3 days of the Hongtsaiping • 2.7 million m3 in volume, non- catastrophic landslide reported after 3 days of the Chi-Chi earthquake
Location of the Hongtsaiping area
Results from various kinds of research Photogrammetry based on orthorectified aerial photographs Maximum displacement 24.7 m (modified from Lee et al., 2004)
Aerial Photogrammetry 1998/06 1999/12 2002/10 (Hongtsaiping) (0.61 m/pixel) overlapped image
Particle Image Velocimetry (PIV) Technique Maximum displacement: 24 m
PIV technique II 3 main sliding areas defined of sliding A1 A2 B (modified from Lo et al., 2006) • Various directions of sliding A1 A2 B
Borehole analysis 13 borehole sites Lithology of sliding mass defined 80 m in thickness BH1 BH2 BH3 BH4 BH5 BH6 BH7 BH8 BH12 BH13 BH9 BH10 BH11 Colluvium with sandstone grain Colluvium with Shale matrix
Nature of colluvium (Ke, 2006)
Nature of ancient landslide Strata and sliding plan curved by geological structure Ancient landslide occurred due to 4 earthquakes in between August 1916 and January 1917. (Huang et al., 2006)
DISTINCT ELEMENT METHOD (DEM)
Reasons for use of the Distinct Element Method Colluvium as the material of the sliding block of the Hongtsaiping landslide → a series of behavior of failure and movement can be applied to the Distinct Element Method. Ancient and present landslides are large-scaled behavior of transformation which is one of features of the Distinct Element Method.
Particle Flow in Code 2 Dimension (PFC2D) Tsaoling landslides, (Tang et al., 2009)
The Hongtsaiping landslide before the Chi-Chi earthquake Pink line: Topography before the Chi-Chi earthquake (Chang, 2007)
The landslide model triggered by the Chi-Chi earthquake 20 meters Maximal displacement: 18 m Movement duration: 160 seconds (Chang, 2007)
3D model building According to borehole and the region of surface displacement data to make a reasonable model 40 x 40 m grid Digital Terrain Model (DTM)
Walls building of Hontsaiping landslide for Distinct Element Method model
Walls with balls Radius of balls in upper part is from 2 ~ 3.2 m Radius of balls in lower part is from 1 ~ 1.2 m Number of balls: 20,000
Hongtsaiping landslide Jiufengershan avalanche Summary – comparison between Hongtsaiping landslide and Jiufengershan avalanche Hongtsaiping landslide Jiufengershan avalanche Circular failure Layered colluvium resulted from ancient landslide Maximal 80 m in thickness Friction coefficient of sliding surface is 0.24 F = 1.93 dropped to 0.94 when the Chi-Chi earthquake occurred. Dip-slope slide Intact strata average thickness of 60 m Friction coefficient of the surface of separation is 0.2
THANKS FOR YOUR ATTENTION
Electrical Resistivity Imaging Profile Lower slope Upper slope (Huang et al., 2006)
Micro properties for PFC
Principal of Particle Flow Code (PFC2D Manual, 2002)
Potyondy and Cundall (2004) Type of contact for PFC Mode of contact stiffness Mode of bond Mode of sliding Potyondy and Cundall (2004)