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Environmental Geology

, Volume 55, Issue 6, pp 1269–1277 | Cite as

Numerical modeling of rainstorm-induced shallow landslides in saturated and unsaturated soils

  • Tung-Lin TsaiEmail author
  • Hung-En Chen
  • Jinn-Chuang Yang
Original Article

Abstract

For the assessment of shallow landslides triggered by rainfall, the physically based model coupling the infinite slope stability analysis with the hydrological modeling in nearly saturated soil has commonly been used due to its simplicity. However, in that model the rainfall infiltration in unsaturated soil could not be reliably simulated because a linear diffusion-type Richards’ equation rather than the complete Richards’ equation was used. In addition, the effect of matric suction on the shear strength of soil was not actually considered. Therefore, except the shallow landslide in saturated soil due to groundwater table rise, the shallow landslide induced by the loss in unsaturated shear strength due to the dissipation of matric suction could not be reliably assessed. In this study, a physically based model capable of assessing shallow landslides in variably saturated soils is developed by adopting the complete Richards’ equation with the effect of slope angle in the rainfall infiltration modeling and using the extended Mohr–Coulomb failure criterion to describe the unsaturated shear strength in the soil failure modeling. The influence of rainfall intensity and duration on shallow landslide is investigated using the developed model. The result shows that the rainfall intensity and duration seem to have similar influence on shallow landslides respectively triggered by the increase of positive pore water pressure in saturated soil and induced by the dissipation of matric suction in unsaturated soil. The rainfall duration threshold decreases with the increase in rainfall intensity, but remains constant for large rainfall intensity.

Keywords

Shallow landslide Saturated and unsaturated soils Rainstorm 

List of symbols

C

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

C0

the minimum value of C

c

effective cohesion

D0

\({K_{s}} \mathord{\left/{\vphantom {{K_{s}} {C_{0}}}} \right.\kern-\nulldelimiterspace} {C_{0}}\)

dZ

water depth

dLZ

slope depth

FS

factor of safety

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

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 moisture content

θr

residual moisture content

α

slope angle

ϕ′

effective friction angle

ϕb

the friction ϕ angle with respect to the matric suction

ζ

fitting parameter

γ

the unit weight of soil

γw

the unit weight of water

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Civil and Water Resources EngineeringNational Chiayi UniversityChiayi CityTaiwan
  2. 2.Department of Civil EngineeringNational Chiao Tung UniversityHsinchu CityTaiwan

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