New Conceptual Model of Large-Scale Landslide

Transcription

1 The Second Global Summit of Research Institutes for Disaster Risk Reduction Development of a Research Road Map for the Next Decade March 19-20, 2015 New Conceptual Model of Large-Scale Landslide Reported by Chjeng Lun, Shieh Director, Disaster Prevention Research Center National Cheng Kung University

2 To review historical disasters from 1950, LSL & MSD occur frequently 凡梅南溫葛 妮颱風( 53 ) Winnie typhoon 樂禮颱風( 63 ) Gloria typhoon 賀 畢莉颱風( 76 ) Billie typhoon 琳恩颱風( 87 ) Lynn typhoon 伯颱風( 96 ) Herb typhoon Chi-Chi Earthquake 象神颱風( 00 ) Typhoon Xangsane 敏艾海馬 桃納利颱颱風( 芝莉督棠颱颱利颱風風風( ( ( ) Aere typhoon ) Mindulle typhoon ) Nari typhoon ) Toraji typhoon 風風( ( ) Masha typhoon ) Haitang typhoon 莎颱 聖卡辛莫芭帕玫樂颱基克風颱颱風風( 07 ( ( ) Sinlaku typhoon ) Kalmaegi typhoon ) Sepat typhoon 拉克Morakot 瑪Parma typhoon Flooding Disaster Sediment Disaster LSL & MSD 那姬比Megi Fanapi typhoon typhoon 瑪都Nanmadol typhoon 蘇12 拉Saola typhoon -2-

3 Typhoon Morakot The storm turned into a typhoon on Aug. 4. Rainfall started on Aug. 6. The eye of the typhoon left Taiwan from Taoyuan at 14:00 on Aug. 8. The rainfall continued until Aug. 10. Path of the center of Typhoon Morakot -3-

4 Disasters of Typhoon Morakot Alisan Station Long duration (91 hours) High intensity (123 mm/hour) Large accumulated rainfall depth (3000 mm-72 hour) Broad extent (one-fifth of Taiwan was covered) Sediment-related disasters in the mountain area located within the range of precipitation > 1,000mm Inundation area located at the downstream of rainfall center in the plain area -4-

5 The relationship between accumulative rainfall and duration of catastrophic typhoons Alisan Station -5-

6 Shieh,

7 The scale and type of the disaster increasing with the frequent appearance of extreme weather -7-

8 Large-scale landslide and compound disaster become a new challenge Area:202 ha Depth:80 meter Volume: 24 million m 3 Before Typhoon Morakot in Hsiaolin Village (FORMOSAT-2) After Typhoon Morakot in Hsiaolin Village (FORMOSAT-2) -8-

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10 LESSONS FROM THE DISASTER OF HSIAOLIN VILLAGE Compound Disaster, included shallow landslide, debris flow, flooding, large-scale landslide, natural dam break, occurred in Hsiaolin village The main disaster is caused by large-scale landslide. Mitigation Strategies of Large-scale Landslide Disaster in Taiwan -10-

11 IDEA FOR MITIGATION STRATEGIES OF L.S.L. (6Ws1H) Where Potential Area What Risk analysis (Influence Area) Why On-site monitoring When Forecast and Warning System Who Evacuation Plan How Training, Drills, Education -11-

12 On-site monitoring Forecast and Warning System All the monitor result to setup the warning system, such as rainfall, groundwater level, surface deformation. How to combine all the result together? -12-

13 To Review Landslide cases in typhoon Morakot, 2009 Group A is classified as new born landslide, and group B include enlarge case and combine case New Born Case B 布唐布納斯溪 mm A mm 萬山 Cumulative rainfall >1,000 mm After rainfall peak near the turning point of accumulative rainfall Enlarge & Combine case B A Cumulative rainfall is about mm Before rainfall peak -13-

14 of Large-scale Landslide in Taiwan Definition of Large-scale Landslide Area > 10 ha Depth > 10 m Volume > 10 4 m 3-14-

15 Fast-moving landslide was caused by typhoon. Hsiaolin Village, Kaohsiung County in Time:August/06-10 (Typhoon Morakot) Area of landslide:202 ha Depth of landslide:80 m Slope:22 Movement Distance: 2000 m Accumulative Rainfall:2583 mm Loose soil mass With the imprint of groundwater -15-

16 Fast-moving landslide was caused by typhoon Taimali River, Taitung County in 2009 Time:August/06-10 (Typhoon Morakot) Area of landslide:290 ha Depth of landslide:200 m Slope:22 Movement Distance: 1000 m Accumulative Rainfall:1400 mm Loose soil mass With the imprint of groundwater -16-

17 Slow-moving landslide was caused by rainfall Lushan landslide, Nantou since 1994 Area of landslide:30 ha Depth of landslide:~100 m Slope:22 Mass movement With the imprint of groundwater 廬山地滑監測及後續治理規劃, 黎明工程,

18 Slow-moving landslide was caused by rainfall Li-San landslide, Taichung, since 1990 Area of landslide:230 ha Depth of landslide:~50 m Slope:22 Movement Distance:800 m With the imprint of groundwater 中華水土保持學報, 颱風降雨期間梨山地滑區邊坡穩定性之數值評估,

19 Similarity of F.M.L and S.M.L. Shallow Landslide (fast-moving landslide) Large-scale Landslide (slow-moving landslide) Large-Scale Landslide (fast-moving landslide) The al Forest, NTU(2012 yr.) Occurrence: < 2 days(typhoon Saola) without the groundwater layer Slope = 22 ~ 29 φ 25 i = 99.5 mm/hr p P = 1132 mm Lushan landslide LIMI, 2003 Occurrence: For decades with the imprint of groundwater Slope = 24 ~ 26 φr 22 ~ 27 i = 30 ~ 35 mm/hr(2005~6 yr.) p P = 820 mm (2006 yr) Hsiaolin Village(2009 yr.) Occurrence: 4 days (Typhoon Morakot) with the imprint of groundwater Slope = 26 φr i p P 21 ~ 25 = 103 mm/hr = 2583mm -19-

20 Difference of F.M.L. and S.M.L. S.M.L F.M.L -20-

21 Safety Factor FF = R D D R = (1 FS) D = Net force acting on sliding block = Ma D dfs (1 FS) = a, where 1 FS = t M dt D dfs a= t M dt dfs a dt D: Driving Force R: Resistance Force M: Mass of sliding block t dfs dt t -21-

22 The flow velocity of infiltration and groundwater is usually small, therefore, what s reason causes the rapid decreasing in F.S.? We are interesting in what kinds of interaction between infiltration and groundwater will trigger sudden failure or creeping landslide. -22-

23 Case I:Air escape from bottom Case III: Air escape from top 0.04 m z z 0 z G Water z z 0 z G Water Air Flow Infiltration Layer Infiltration Layer 0.85 m z h Cavity Layer Seepage z h Cavity Layer Seepage z GW Air Flow Saturated Zone x z GW Saturated Zone x Scale Pore water pressure gauge measure data W p sc wb : weight : porewater pressure -23-

24 Case I: Air escape from bottom p w p t { s s w w } {(1 n) L + Sn h( t) } sin c + (1 n) γ L + Snγ h( t) p ( t) tanϕcosθ S.F.= γ γ θ s s w where, ϕ = 25 ; θ = 30 ; c =

25 Case II: Groundwater upwelling (Illustration) Anticipation of change in pore water pressure p t p w Elevation controlling of groundwater Anticipation of change in S.F. Scale Pore water pressure gauge -25-

26 Case III: Air escape from top p w p t { s s w w } {(1 n) L + Sn h( t) } sin c + (1 n) γ L + Snγ h( t) p ( t) tanϕcosθ S.F.= γ γ θ s s w where, ϕ = 25 ; θ = 30 ; c =

27 Develop the theory from physical phenomenon Equation of mass conservation nsρw + nsρwv w = 0 t n(1 S) ρa + n(1 S) ρav a = 0 t Equation of momentum conservation Dvw nsρw = nsρwg+ ( pwi) + fw Dt Dv n(1 S) ρ = n(1 S) ρ g+ ( p I) + f Dt Dvs * (1 n) ρs = (1 n) ρsg+ σ s + f s Dt a a a a a Interaction among the constituents fw + fs + fa = 0 Equation of state p V a = m M RT -27-

28 Convert the 3-D governing equation into 1-D. Interaction among the constituents in 1-D f buoy f rel -the momentum supplies(interactions) can be divided into two parts : caused by the normal pressure in the constituents surface : the drag force due to the relative velocity tangential to the constituents surface f buoy ns pw n(1 S) pw fw = (1 n) + n z n z rel piw fw = ns z w f s buoy ns p n w ( 1 S) p a fs = (1 n) + (1 n) n z n z rel piw pia fs = ns + n( 1 S ) z z f a buoy n( 1 S) pa n(1 S) pw fa = (1 n) n z n z rel pia fa = n( 1 S) z -28-

29 Governing equation in 1-D form Equation of mass conservation Equation of momentum conservation t t w w w = 0 z n 1 S a { n 1 S ρaua} = 0 z ( nsρ ) + ( nsρ u ) { ( ) ρ } + ( ) Duw pw piw nsρw = nsρwg ns + Dt z z Dua pa pw pia n(1 S) ρa = n(1 S) ρag+ ( ns S n) ( 1 S) n( 1 S) Dt z z z Dus ps piw pw pia pa (1 n) ρs = (1 n) ρsg + S n ( 1 n) + ( 1 S) n ( 1 n) Dt z z z z z Equation of state p za a = m M RT

30 Case I: Air escape from bottom p t p s p w -30-

31 Case II: Groundwater upwelling p w p t p w p s -31-

32 Case III: Air escape from top p w p t p w p s -32-

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34 This model is a pilot study of LSL warning system in Taiwan. More field data are necessary before it is used. The moment of infiltration front touch with groundwater will induce fast-moving LSL. -34-

35 Don t Touch!! -35-