Coupling TRIGRS and TOPMODEL in shallow landslide prediction. 1 Presenter: 王俊皓 Advisor: 李錫堤老師 Date: 2016/10/13

Transcription

1 Coupling TRIGRS and TOPMODEL in shallow landslide prediction 1 Presenter: 王俊皓 Advisor: 李錫堤老師 Date: 016/10/13

2 Outline Introduction Literature review Methodology Pre-result Future work

3 Introduction 3 Motivation Shallow landslide is influenced by groundwater table depth of soil layer, predicting groundwater table depth can analysis slope stability effectively. Coupling hydrology theory to considerate lateral recharge of groundwater.

4 Introduction 4 Approaches to evaluate landslide Statistical approaches : Logistic Regression. Deterministic approaches : Physically-based models Steady state model : SHALSTAB MODEL(Montgomery et al., 1994) Transient model : TRIGRS (Baum et al., 00) Weight Slope angle Friction force

5 Introduction 5 Water behavior of a catchment Rainfall Infiltration Ground surface? Surface runoff Percolation River Groundwater flow Groundwater table Seepage

6 Introduction 6 Flow chart Geology and hydrology parameters Hydrological model(trigrs) Refine groundwater table depth with TOPMODEL Infinite slope model Prediction of landslide occurrence

7 Literature review 7 Literature review Combining an infinite-slope stability calculation with a transient, one-dimensional analytic solution for pore pressure response to transient rainfall infiltration. (Iverson, 000; Baum et al., 00; Savage et al., 003; Godt, 004) TRIGRS models were used for slope stability analysis in Taiwan. (C.C. Wu, 006; P.C. Wang, 007; S.H. Chung, 008) Concept of topographic index, ln(a/tanβ), and TOPMODEL. (Beven and Kirkby, 1979) A hydrological simulation based on a modified version of TOPMODEL was developed to estimate the temporal groundwater level for conducting the slope-instability analysis. (K.T. Lee, 009) Coupling TRIGRS and TOPMODEL. (H.W. Lee, 011)

8 Methodology 8 Diffusion equation(iverson, 000): φ t = ( D 0 cos δ ) φ z φ: Groundwater pressure head [L] t: Time [T] δ: Slope angle [ ] D 0 : Saturated hydraulic diffusivity [L /T] z: Depth in vertical direction [L] φ Z, t = Z d z cos δ I ZLT + N n=1 N n=1 InZ InZ TRIGRS(Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis) (Baum et al., 00) A solution for pore pressure in the case of an impermeable basal boundary at a finite depth: K s D 0 H t t K n [ s cos δ (t t n)] D 0 Steady state H t t K n+1 [ s cos δ (t t n+1)] 1 m=1 1 m=1 ierfc ierfc Z: Vertical coordinate direction depth below the ground surface [L] t: Time [T] d z : Steady-state depth of the water table measured in the vertical direction [L] I ZLT : Steady (initial) surface flux [L/T] I nz : Surface flux of a given intensity for the n th time interval [L/T] d Lz : Depth of the impermeable basal boundary measured in the Z direction [L] N: Total number of time intervals H t t n : Heaviside step function and nt is the time at the th n time interval in the rainfall infiltration sequence ierfc x = 1 π e x x erfc(x) erfc x = x π 0 e t dt m 1 d Lz (d Lz Z) D 0 cos δ (t t n)] 1 m 1 d Lz (d Lz Z) D 0 cos δ (t t n+1)] (complementary error function) φ Z, t =0 Z = Groundwater table depth 1 + ierfc + ierfc m 1 d Lz + (d Lz Z) D 0 cos δ (t t n)] 1 m 1 d Lz + (d LZ Z) D 0 cos δ (t t n+1)] 1

9 Methodology 9 TOPMODEL(TOPgraphy based hydrological MODEL) (Beven. et al., 1979) TOPMODEL T is exponental decreasing with groundwater depth: T = T 0 e (z j m ) T: Lateral transmissivity of aquifer [L /T] T 0 : Lateral saturated transmissivity of ground surface [L /T] z j : Groundwater table depth in j-th grid [L] m: Coefficient of soil [L] S rz : Root zone S uz : Unsaturated zone D:Soil Depth Z w :Water table height q v :Vertical infiltration rate S rz S uz Groundwater table q v Z w

10 Methodology TRIGRS 10 Refine groundwater table depth a z j = z + m λ ln tan β j λ: Average topographic index m: Coefficient of soil [L] a: Specific catchment area [L] z: Mean groundwater depth of a catchment [m] TI(topographic index )= ln a tan β Unit contour length b Specific catchment Catchment area Area a=a/b a = A/b Contributing area A Stream line Contour line

11 11 Infinite Slope MODEL FS = resistance force driving force = τ r τ d Z = C + (γ sz γ w Z w )cos β tan ψ γ s Z sin β cos β C: Cohesion [M/LT ] γ s : Total unit weight of soil [M/L T ] γ w : Water unit weight [M/L T ] Z : Soil depth [L] Z w : Groundwater height [L] β: Slope angle [ ] ψ: Friction angle [ ] Groundwater table FS>1 Stable FS<1 Unstable β Weight Bedrock Friction force Z w

12 Pre-result 1 Sub-river basin of Tahan river basin: Piya (H.W. Lee, 011) Elevation (m)

13 13 C(cohesion) δ(slope angle) (N/m ) ( ) Pre-result Input parameter NDVI i, j + 1 C = C max Parameter Production Cohesion (Chung, 008) Slope angle Calculate from DTM. d Lz (depth of soil) Depth of soil (Chung, 008) (m)

14 14 Pre-result K s (hydraulic conductivity) (m/s) γ s (total unit weight of soil) Input parameter (N/m 3 ) Parameter Production Hydraulic conductivity (Chung, 008) Total unit weight of soil (Chung, 008) D 0 (diffusivity) Diffusivity (Chung, 008) (m /s)

15 Pre-result 15 Input parameter Parameter Production W i (initial groundwater depth) (m) Initial groundwater depth (Lee, 008) Topographic index(ti) (Lee, 008) Soil coefficient(m = 0.06) (Lee, 008) TI(topogratphic index) a z j = z + m λ ln tan β j λ: Average topographic index (5.384) m: Modulus parameter [L] (0.06) a: Specific catchment area [L] z: Mean groundwater depth of a catchment [m] TI(topographic index )= ln a tan β

16 Pre-result Pre-Result 16 Assume uniform rainfall (m) (m)

17 Future work 17 Future work Select new rainfall event and digit landslide inventory. Require more geology and hydrology parameters: Field sampling, Field test, Laboratory test.

18 18 Thanks for attention!