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

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Environmental Geology

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.

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Abbreviations

C :

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

C 0 :

the minimum value of C

c′:

effective cohesion

D 0 :

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

d Z :

water depth

d LZ :

slope depth

FS:

factor of safety

I Z :

rainfall intensity

K s :

saturated hydraulic conductivity

K L :

hydraulic conductivity in lateral direction (x and y)

K z :

hydraulic conductivities in slope–normal direction (z)

S :

the degree of saturation

M :

fitting parameter

N :

fitting parameter

T :

rainfall duration

u a :

pore air pressure

u w :

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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Authors and Affiliations

  1. Department of Civil and Water Resources Engineering, National Chiayi University, 300 Sefu Road, Chiayi City, 60004, Taiwan

    Tung-Lin Tsai

  2. Department of Civil Engineering, National Chiao Tung University, Hsinchu City, Taiwan

    Hung-En Chen & Jinn-Chuang Yang

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  1. Tung-Lin Tsai
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  2. Hung-En Chen
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  3. Jinn-Chuang Yang
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Correspondence to Tung-Lin Tsai.

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Tsai, TL., Chen, HE. & Yang, JC. Numerical modeling of rainstorm-induced shallow landslides in saturated and unsaturated soils. Environ Geol 55, 1269–1277 (2008). https://doi.org/10.1007/s00254-007-1075-1

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