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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

Abstract

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.

Keywords

Shallow landslides Degree of saturation Unit weight Unsaturated shear strength 

List of symbols

C

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

c

Effective cohesion

dZ

Water depth

dLZ

Slope depth

FS

Factor of safety

Gs

The specific gravity of soil solid

IZ

Rainfall intensity

Ks

Saturated hydraulic conductivity

KL

Hydraulic conductivity in lateral direction (x and y)

Kz

Hydraulic conductivities in slope-normal direction (z)

S

The degree of saturation

Sr

The residual degree of saturation

Se

The effective saturation

M

Fitting parameter

N

Fitting parameter

T

Rainfall duration

ua

Pore air pressure

uw

Pore water pressure

Z

The coordinates

σ

Total normal stress

ψ

Groundwater pressure head

θ

Soil volumetric water content

θs

Saturated volumetric water content

θr

Residual volumetric water content

α

Slope angle

\( \phi^{\prime} \)

Effective friction angle

\( \phi^{b} \)

The friction angle with respect to the matric suction

ζ

Fitting parameter

χ

The parameter for shear strength of unsaturated soil

\( \overline{\gamma } \)

The depth-averaged unit weight of soil

γw

The unit weight of water

Notes

Acknowledgments

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

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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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