Environmental Earth Sciences

, Volume 59, Issue 6, pp 1285–1295 | Cite as

Effects of degree of saturation on shallow landslides triggered by rainfall

  • Tung-Lin TsaiEmail author
  • Hsin-Fa Chen
Original Article


The empirical rainfall threshold concept and the physical-based model are two commonly used approaches for the assessment of shallow landslides triggered by rainfall. To investigate in detail the rainfall-triggered shallow landslides, many physical-based models coupling the infinite slope stability analysis with the rainfall infiltration modeling in variably saturated soil were developed. However, in those physical-based shallow landslide models, the unit weight and the unsaturated shear strength were assumed constant rather than depending on the degree of saturation. In this study, the effects of the unit weight and the unsaturated shear strength as function of degree of saturation on rainfall-triggered shallow landslides are examined. Several designed scenarios and a real case scenario are used to conduct the examinations. The results show that not only the occurrence of shallow landslides but also the failure depth and the time to failure could be misassessed if the influences of degree of saturation on the unit weight and the unsaturated shear strength are neglected.


Shallow landslides Degree of saturation Unit weight Unsaturated shear strength 

List of symbols


The change in volumetric water content per unit change in pressure head


Effective cohesion


Water depth


Slope depth


Factor of safety


The specific gravity of soil solid


Rainfall intensity


Saturated hydraulic conductivity


Hydraulic conductivity in lateral direction (x and y)


Hydraulic conductivities in slope-normal direction (z)


The degree of saturation


The residual degree of saturation


The effective saturation


Fitting parameter


Fitting parameter


Rainfall duration


Pore air pressure


Pore water pressure


The coordinates


Total normal stress


Groundwater pressure head


Soil volumetric water content


Saturated volumetric water content


Residual volumetric water content


Slope angle

\( \phi^{\prime} \)

Effective friction angle

\( \phi^{b} \)

The friction angle with respect to the matric suction


Fitting parameter


The parameter for shear strength of unsaturated soil

\( \overline{\gamma } \)

The depth-averaged unit weight of soil


The unit weight of water



This study was funded by the National Science Council of the Republic of China under Grant No. NSC 97-2625-M-415-001.


  1. Anderson MG, Howes S (1985) Development of application of a combined soil water-slope stability model. Q J Eng Geol Lond 18:225–236CrossRefGoogle Scholar
  2. Baum RL, Savage WZ, Godt JW (2002) TRIGRS—Fortran program for transient rainfall infiltration and grid-based regional slope-stability analysis, Virginia, US Geological Survey Open file report 02-424Google Scholar
  3. Bear J (1972) Dynamics of fluids in porous media. Dover, New YorkGoogle Scholar
  4. Bishop AW (1954) The use of pore pressure coefficients in practice. Geotechnique 4:148–152CrossRefGoogle Scholar
  5. Borga M, Fontana GD, De Ros D, Marchi L (1998) Shallow landslide hazard assessment using a physically based model and digital elevation data. Environ Geol 35:81–88CrossRefGoogle Scholar
  6. Chen B (2005) A study on characteristics and hazard assessment of landslides in Shihmen Reservoir watershed, northern Taiwan. Ph. D. thesis, National Chung Hsing University, Taichung, TaiwanGoogle Scholar
  7. Collins BD, Znidarcic D (2004) Stability analyses of rainfall induced landslides. J Geotech Geoenviron Eng 130(4):362–372CrossRefGoogle Scholar
  8. Crosta GB, Frattini P (2003) Distributed modeling of shallow landslides triggered by intense rainfall. Nat Hazards Earth Syst Sci 3:81–93CrossRefGoogle Scholar
  9. D’Odorico P, Fagherazzi S, Rigon R (2005) Potential for landsliding: dependence on hyetograph characteristics. J Geophys Res, Earth Surface 110(F1)Google Scholar
  10. Escario V, Juca J, Coppe MS (1989) Strength and deformation of partly saturated soils. In: Proceeding of 12th international conference on soil mechanics and foundation engineering, vol 3, Rio de Janeiro, pp 43–46Google Scholar
  11. Frattini P, Crosta GB, Fusi N, Negro PD (2004) Shallow landslides in pyroclastic soil: a distributed modeling approach for hazard assessment. Eng Geol 73:277–295CrossRefGoogle Scholar
  12. Fredlund DG, Morgenstern NR, Widger RA (1978) The shear strength of unsaturated soils. Can Geotech J 15:313–321CrossRefGoogle Scholar
  13. Gan JK, Fredlund DG, Rahardjo H (1988) Determination of the shear strength parameters of an unsaturated soil using the direct shear test. Can Geotech J 25:500–510CrossRefGoogle Scholar
  14. Genuchten Van (1980) A closed-form equation for predicting hydraulic conductivity of unsaturated soils. Soil Sci Soc Am J 44:892–898Google Scholar
  15. Hills RG, Hudson DB, Wierenga DB (1989) Modeling one-dimensional infiltration into very dry soils 1. model development and evaluation. Water Resour Res 25:1259–1269CrossRefGoogle Scholar
  16. Hsu SH, Ni CF, Hung PF (2002) Assessment of three infiltration formulas based on model fitting on Richards’ equation. J Hydrol Eng 7(5):373–379CrossRefGoogle Scholar
  17. Hurley DG, Pantelis G (1985) Unsaturated and saturated flow through a thin porous layer on a hillslope. Water Resour Res 21:821–824CrossRefGoogle Scholar
  18. Iverson RM (2000) Landslide triggering by rain infiltration. Water Resour Res 36:1897–1910CrossRefGoogle Scholar
  19. Keim RF, Skauqset AE (2003) Modelling effects of forest canopies on slope stability. Hydrol Process 17:1457–1467CrossRefGoogle Scholar
  20. Lan HX, Lee CF, Zhou CH, Martin CD (2005) Dynamic characteristics analysis of shallow landslides in response to rainfall event using GIS. Env Geol 47:254–267CrossRefGoogle Scholar
  21. Lu N, Likos WJ (2004) Unsaturated soil mechanics. Wiley, New JerseyGoogle Scholar
  22. Montgomery DR, Dietrich WE (1994) A physically based model for the topographic control on shallow landslide. Water Resour Res 30:83–92Google Scholar
  23. Morrissey MM, Wieczorek GF, Morgan BA (2001) A comparative analysis of hazard models for predicting debris flows in Madison County, Virginia. US Geological Survey Open file report 01-67Google Scholar
  24. Richards LA (1931) Capillary conduction of liquids in porous mediums. Physics 1:318–333CrossRefGoogle Scholar
  25. Tarantino A, Bosco G (2000) Role of soil suction in understanding the triggering mechanisms of flow slides associated with rainfall. In: Wieczorek GF, Naeser ND (eds) Debris-flow hazards mitigation: mechanics, prediction, and assessment. Proceedings of the second international conference on debris-flow hazards mitigation, Taipei, Taiwan, 16–18 August 2000. A.A.Balkema, Rotterdam, pp 81–88Google Scholar
  26. Tsai TL (2008) The influence of rainstorm pattern on shallow landslide. Environ Geol 53(7):1563–1569CrossRefGoogle Scholar
  27. Tsai TL, Yang JC (2006) Modeling of rainfall-triggered shallow landslide. Env Geol 50(4):525–534CrossRefGoogle Scholar
  28. Tsai TL, Chen HE, Yang JC (2008) Numerical modeling of rainstorm-triggered shallow landslides in saturated and unsaturated soils. Env Geol 55(6):1269–1277CrossRefGoogle Scholar
  29. Vanapalli SK, Fredlund DG (2000) Comparison of empirical procedures to predict the shear strength of unsaturated soils using the soil–water characteristic curve. In: Shackelford CD, Houston SL, Chang NY (eds) Advances in unsaturated geotechnics. GPS No.99, ASCE, Reston, pp 195–209Google Scholar
  30. Vanapalli SK, Fredlund DG, Pufahl DE, Clifton AW (1996) Model for the prediction of shear strength with respect to soil suction. Can Geotech J 33:379–392CrossRefGoogle Scholar
  31. Wallach R, Grigorin G, Rivlin J (1997) The errors in surface runoff prediction by neglecting the relationship between infiltration rate and overland flow depth. J Hydrol 200:243–259CrossRefGoogle Scholar
  32. Wu W, Sidle RC (1995) A distributed slope stability model for steep forested basins. Water Resour Res 31:2097–2110CrossRefGoogle Scholar
  33. Yang JC, Tsai TL, Huang AB (2008) A study on risk assessment of landslide and sediment deposition in Shihmen watershed. Rep. No. MOEAWRA0970151, Water Resources Agency. Ministry of Economic Affairs, Taipei, TaiwanGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of Civil and Water Resources EngineeringNational Chiayi UniversityChiayiTaiwan
  2. 2.Chiayi Forest District Office, Forestry BureauChiayiTaiwan

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