Tsao-Ling rockslides, Taiwan 1 Ju-Jiang Hung Department of Civil Engineering, National Taiwan University, Taipei, Taiwan Chyi-Tyi Lee Ming-Lang Lin Institute of Applied Geology, National Central University, Chungli, Taiwan 報告者：邱奕勛 指導老師：李錫堤老師 報告日期： 2011/01/06

Introduction Method Result and discussion Conclusion 2 OUTLINE

Rockslide (Hung and Chen, 2001) Many landslide disasters occur every year on the mountainous island of Taiwan. The collision between the Philippine Sea plate and the Eurasian continental plate is active. A dip slope in interbedded Pliocene sandstones, mudstones, and shales. 3 Introduction Location map of site of Tsao-Ling rockslides, central Taiwan

Historical events at Tsao-Ling rockslide, Taiwan, DateTriggerProcessEffectsReferences June 6, 1862Earthquake (M = )Landslide; formation of a landslide dam.*┼1, 2, 4, 5, UnknownBreach of the landslide dam.*┼5, 6 December 17, 1941Earthquake (M = 7.1)Landslide-84 x 10 6 m 3 in volume(13) ; formation of a landslide dam m in height, formation of a dammed up lake containing 12.8 M m 3 of water. 36 persons killed; 59 houses damaged. 1, 2, 3, 4, 5, 6,7 August 10, 1942Rainfall: 3 day cumulative precipitation of 770 mm Landslide-100 x 10 6 m 3 in volume(11); height of landslide dam increased from m in height; formation of a larger dammed up lake containing 157 x 10 6 m 3 of water. 1 person buried; 1 house damaged. 2, 3, 4, 5, 6, 7 May 18, 1951Rainfall: 5 day cumulative precipitation of 776 mm Break of the landslide dam. Release of 120 x 10 6 m 3 of water. Flooding of 3000 ha of arable land; 137 persons killed: 1200 houses damaged. 2, 3, 4, 5, 6, 7 August 15, 1979Rainfall: 2 day cumulative precipitation of 327 mm Landslide-26 x 10 6 m 3 in volume(29); formation of a dammed up lake containing 40 x 10 6 m 3 of water. 4, 5, 6, 7 August 24, 1979Rainfall: 2 day cumulative precipitation of 624 mm Breach of the landslide dam. Release of 40 x 10 6 m 3 of water. Two bridges destroyed. 4, 5, 6, 7 September 21, 1999Chi-Chi earthquake (M=7.3) Landslide-125x 10 6 m 3 in volume (9) ； forming a 5-km-long lake. 29 lives were lost *:Interview of Tsao-Ling villagers by Hung in ┼: Authors were unable to obtain significant data. References: 1-Tai-Pei Observatory (1942); 2-Hsu (1951 ); 3-Hsu and Leung (1977); 4-Hung (1980); 5-Chang (1984); 6-Chang and Lee (1989); 7-Lee et al. (1993). 4

5 Geology of the Tsao-Ling slopes Stratigraphy and lithology in the Tsao-Ling area

6 Generalized geologic map of Tsao-Ling rockslide area

Tsao-Ling area before December 17, Topographic map of Tsao-Ling rockslide area before December 17, 1941 Reconstructed profiles of 1941 and 1942 slides

1941 Tsao-Ling rockslide event 8 Intensity contour map of 1942 Chia-Yi earthquake

1941 Tsao-Ling rockslide event 9 Simplified map of Tsao-Ling rockslide area after December 17, 1941, and before March 30, 1942 Reconstructed profiles of 1941 and 1942 slides

1942 Tsao-Ling rockslide event 10 Reconstructed profiles of 1941 and 1942 slides

11 General view of head scarp and remaining slope, looking from landslide dam toward remaining slope and head scarp

12 Remote view of remaining part of landslide dam, looking from top of head scarp

1979 events at Tsao-Ling rockslide 13 Reconstructed profiles of 1979 slide

14 Close-up view of small part of sliding surface, August 22, 1979, 1 week after sliding

15 View upstream of dammed lake and landslide dam, looking from toe of remaining slope

16 Aerial photograph of 1979 rockslide event on August 19, 1979, 4 days after slide and 4 days before overtopping

17 Aerial photograph, taken in 1980, of greater Tsao-Ling area

18 Topographic map of Tsao-Ling rockslide area in 1977 Reconstructed profiles of 1979 slide

Earthquake The peak ground acceleration at the Tsao-Ling slope may be estimated by local attenuation equations: 19 Triggers for the Tsao-Ling events M : local magnitude a : peak ground acceleration R : the distance to hypocenter of the earthquake

Precipitation From 1949 to 1960, the annual mean rainfall in the Tsao-Ling area was 3000 mm, while that in the ALi-Shan station was 4000 mm. 20

Relationship of landslides to geology 21 Orientation of joint sets in the Tsao-Ling rockslide area

22 Sliding plane aef

Boring and sampling 23 Laboratory analysis

24 Summary of index test results on block samples

25 Practice size distribution of block samples

26 Optical mineralogy of block samples

27 Clay mineral of block samples

28 Results of slake durability on block samples

29 Ground water

30 Tsao-Ling landslide induced by 1999 Chi-Chi Earthquake Topographic profiles based on the 40×40 m 1989 DEM and the 2002 LIDAR mapping (Chen, 2006)

31 View up sliding surface of September 1999 rockslide on Tsao-Ling dip slope, triggered by Chi-Chi earthquake

32 Topographic changes of the Tsao-Ling landslide induced by the 1999 Chi-Chi earthquake(Chen, 2005)

33 (Tang, 2009)

The sliding plane of the 1941and 1942 slide is located at or near the Cho-Lan-Chin-Shui boundary ; the 1979 sliding plane located in the middle part of Chin-Shui shale formation. They are nonplastic or low-plastic silty or c1ayey materials in nature. Quartz and c1ay minerals are the two most abundant minerals in these shaley formations. X-ray diffractometer analyses show that the clay fraction of the shale contains very little or no montmorillonite. Expansion tests also show that the shale has very little (0.25%) expansion upon saturation. When the residual friction coefficient of Tsao-Ling landslide is equal or less than 0.05 after a critical displacement due to the Chi-Chi earthquake, the landslide block can move across the Ching-shui River and deposit on Diagiaoshan. 34 Conclusion

35 Thank for your attention

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