r.rotstab: a GRASS-based deterministic model for deep-seated landslide susceptibility over large areas Martin Mergili 1 , Ivan Marchesini 2 , Mauro Rossi 2 , Fausto Guzzetti 2 , Wolfgang Fellin 3 1 Institute of Applied Geology, BOKU University, Vienna, Austria 2 CNR IRPI, Perugia Italy 3 Geotechnical and Tunnel Engineering, University of Innsbruck, Austria 1 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
Content > 1 Slope stability modelling > 2 The 3D slope stability model r.rotstab > 3 The Collazzone test area > 4 Model results > 5 Conclusions and outlook 2 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
1 Slope stability modelling Infinite slope stability model c ... cohesion soil + roots (N/m²) γ d ... specific weight of dry soil (N/m³) φ ... angle of internal friction (°) γ w ... specific weight of water (N/m³) θ s ... sat. water content (vol.-%) buoyancy θ s G' = γ d d + θ s γ w d sub − γ w d sub γ d d sub weight of φ moist soil .... = γ d d + ( θ s − 1 ) γ w d sub γ w c seepage force S = γ w d sub sin β d normal force N = G 'cos β β shear resistance R = N tan ϕ + c / cos β shear force T = G 'sin β + S FS inf > 1: slope is stable T = c / cos β + N tan ϕ FS inf = R T FS inf < 1: slope is not stable > The infinite slope stability model is often coupled with slope hydraulics ( SHALSTAB , SINMAP or TRIGRS ) 3 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
1 Slope stability modelling Shallow and deep-seated landslides Photo: USGS The infinite slope stability model is only applicable to shallow translational slides in cohesionless regolith. It shall not be used for modelling of rotational slope failures and deep-seated mass movements shallow deep-seated translational failure rotational failure 4 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
1 Slope stability modelling Slip circle model inter-column forces slip circle forces are shown for every second column only > The basic static principle is the same as with the infinite slope stability model, but different methods for the application with curved failure planes exist Bishop (1954), Janbu et al. (1956), Hovland (1977) 5 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
1 Slope stability modelling Random search for critical slip surface 3 1 1 1 FS = 0.67 FS = 0.67 2 2 FS = 1.83 3 FS = 1.16 no pixel-based approach application with GIS non-trivial 6 6 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
1 Slope stability modelling 3D slip circle models > The proof of slide stability is a standard task of geotechnical investigations, many software packages are therefore available > Many programs are based on longitudinal profiles, 3D models exist as well www.clara-w.com ( Hungr, 1988 ) > Few attempts with GIS Xie et al. (2003, 2004a, b, 2006), Marchesini et al. (2009) 7 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab GRASS GIS > GIS-supported 3D slope stability model for >> single landslides with a priori known failure plane >> identification of the most critical slip surface of single slopes >> slope stability mapping for larger areas where the infinite slope stability model is not suitable > Freely available to experts dealing with slope stability problems 8 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab r.rotstab – implementation shell script r.rotstab.sh C code with terminal interface r.rotstab run within GRASS GIS GRASS raster module data input data preprocessing simulation start of simulation post-processing of results display and export of results 9 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab Slip surface geometry possible slip sphere surface geometries ellipsoid truncated ellipsoid 10 10 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab Orientation of potential slip surfaces (a) ground plot y z' = z (b) longi- y' z'' tudinal x' section a c along x' a r·a P1‘ x' P1 P2 r·a r·a z b β x α D b r·a P2‘ f o n e o p x'' i t o c l e s r t i s L d e p e e t s randomization of center coordinates, a , b , c , z b and r option to skip randomization and to work with defined parameters 11 11 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab 3D safety factor FS 3D = ∑ C ( cA + ( G 'cos β m + N s ) tan ϕ ) cos β m ∑ C ( G 'sin β m + T s ) cos β m modified after Hovland, 1977, Xie et al., 2003, 2004a, b, 2006 forces are shown for every second column only sum of stabilizing and destabilizing forces over all columns inter-column forces are neglected ( Fellenius appoach) 12 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab Spatial discretization bedrock test of many randomly selected slip surfaces minimum FS and depth of slip surface if FS < 1 are determined for each raster cell 13 13 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab γ d , c , φ, θ s , ellipsoid parameters geometry random ellipsoid other ellipsoids r.rotstab – logical slip surface other slip surfaces framework input column 1 column 2 other columns ellipsoid level G‘ , S G‘ , S slip surface level R T R T column level raster cell level factor of safety FS 3D critical slip surface? minimum factor of safety FS 3D deepest slip surface with FS 3D < 1 factor of safety factor of safety depth of slip surface depth of slip surface 14 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab Test against established models Hungr et al., 1989 Leshchinsky et al., 1985 Xie et al, 2006 Lam and Fredlund, 1993 Hungr et al., 1989 and others Xie et al., 2006 Xie et al, 2006 15 15 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
2 The 3D slope stability model r.rotstab Test against established models (c) slip surface 1 (c) slip (c) slip cell size / (b) with (b) with cell with / without surface 2 surface model (a) C1 C2 size weak layer dry moist Results with r.rotstab (version with Hovland 3D model) 0.02 m 1.43 1.19 1.28 0.5 m 2.03 / 2.02 1.58 1.53 0.05 m 1.38 1.18 1.27 1.0 m 2.10 / 2.05 1.58 1.53 0.10 m 1.35 1.16 1.26 2.0 m 2.04 / 2.02 1.53 1.48 Results with 3DSlopeGIS (Xie et al., 2006) Hovland 3D 1.43 1.19 1.25 2.09 1.57 1.49 Bishop 3D 1.43 1.20 1.31 2.28 1.71 1.62 Janbu 3D 1.40 1.22 1.29 2.04 1.61 1.54 Revised Hovland 3D 1.38 1.18 1.27 2.30 1.67 1.57 16 16 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
3 The Collazzone test area 17 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
3 The Collazzone test area Landslide inventory and lithology 18 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
3 The Collazzone test area Slope 19 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
3 The Collazzone test area Geotechnical data Angle of internal cohesion saturated dry specific weight friction water content c ( d = 1.3 m) kN m -2 c ( d = 20 m) kN m -2 θ s φ ° γ d vol.-% c 95 c 98 c 90 c 95 c 98 c 90 Class kN m -3 Sand 19 0.5* 0.5* 0.5* 4.0* 4.0* 4.0* 38 40 Clay 22 0.0 1.8 4.5 0.0 15.5 40.0 18 45 Flysch deposit 18 1.8 3.1 4.8 16.0 27.5 44.0 15 45 Gravel, sand, silt 19 1.5* 1.5* 1.5* 13.0* 13.0* 13.0* 30 45 and clay Sand, silt and clay 18 0.9 2.5 4.6 7.5 21.5 42.0 15 45 Sandstone 22 0.0 2.1 4.0 0.0 16.0 34.0 35 45 Conglomerate 22 1.0* 1.0* 2.1 8.5* 8.5* 17.0 35 45 Limestone 22 1.5* 1.5* 1.5* 13.0* 13.0* 13.0* 35 45 Travertine 22 1.0* 1.0* 1.0* 8.5* 8.5* 8.5* 35 45 20 Presentation OGRS 2012 Yverdon, October 2012 r.rotstab: a GRASS-based deterministic model for landslide susceptibility analysis
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