# Numerical modeling of the 2008 Wenchuan earthquake-triggered Niumiangou landslide considering effects of pore-water pressure

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## Abstract

Ring-shear experiments are commonly conducted to analyze the kinematic mechanisms of landslides triggered by earthquakes, particularly for landslides impacted by pore-water pressure near the grain-crushing sliding surface. However, pore-water pressure is rarely considered in numerical simulation of the post-failure behavior of earthquake-induced landslides. In this paper, a pore-water pressure model based on the results of ring-shear tests (Cui et al. Landslides 14(3):1–15, 2016) is incorporated into the discontinuous deformation analysis (DDA) for modeling and further understanding the initiation and motion behaviors of the Niumiangou landslide triggered by the 2008 Wenchuan earthquake. The pore-water pressure can be recalculated in each time step before the sliding block is detached from the base in the source area, and the friction coefficient of the sliding surface is simultaneously updated according to the pore-water pressure ratio in the modified DDA. The modified pore-water pressure DDA (PWP-DDA) is validated by means of comparison with the analytical results of the dynamic behaviors of a sliding block on an inclined plane under dynamic acceleration. The simulation results indicate that the pore-water pressure on the sliding surface of the Niumiangou landslide sharply increases within a short period, with small relative displacement of the landslide. Relative to the simulated results from the unmodified DDA, the pore-water pressure calculated by the PWP-DDA promotes higher velocity and longer run-out of the sliding mass. Moreover, the modeling run-out and deposit pattern from the PWP-DDA are in basic agreement with the topography of an actual survey.

## Keywords

Earthquake-induced landslide Pore-water pressure Ring-shear experiment Discontinuous deformation analysis Niumiangou landslide## Notations

*a*_{2}Absolute acceleration of sliding block

*a*_{d}Downward critical acceleration

*a*_{E − W}Seismic acceleration record in E-W direction

*a*_{H}Horizontal dynamic acceleration

*a*_{N − S}Seismic acceleration record in N-S direction

*a*_{u}Upward critical acceleration

*a*_{V}Vertical dynamic acceleration

*b*Parameter that governs the stress–displacement behavior of unloading–reloading

*B*_{p}Breakage potential at current time

*B*_{p0}Intial loading breakage potential

*B*_{pl}After loading breakage potential

*c*Cohesive strength

*D*A factor which depends on the degree of disturbance to which the rock mass has been subjected by blast damage and stress relaxation

*e*_{0}Initial void ratio

*f*Friction force

*g*Gravitional acceleration

*GSI*Abbreviation of “Geological Strength Index”

*h*Crushing hardness

*m*Mass of the sliding block

*m*_{i}Material constant

*n*Parameter that governs the sharpness of the transformation from the linear to the nonlinear stress–displacement scope

*n*_{b}Breakage number

*n*_{s}Shape number

*N*Normal support force

*p*Pore-water pressure

*p*_{a}Atmospheric pressure

*s*Parameter defined in Eq. (14)

*S*_{t}Parameter defined in Eq. (2)

*t*(Time)

*u*(Displacement)

- \( \dot{u} \)
(Velocity)

*u*_{y}Parameter governing the elasto-plastic displacement tolerance

*V*_{1}Velocity of base block

*V*_{2}Velocity of sliding block

*α*Inclination angle

*γ*Unit weight of rock mass.

*γ*_{u}Pore-water pressure ratio

*ζ*Parameter defined in Eq. (5)

*λ*Pore-pressure–breakage coefficient

*μ*Coulomb friction coefficient

*ξ*Breakage coefficient

*σ*_{ci}Uniaxial compressive strength of the intact rock pieces

- \( {\sigma}_n^{,} \)
Effective normal stress

- \( {\sigma}_{n0}^{,} \)
Initial effective normal stress

*τ*Shear stress

*τ*_{y}Ultimate shear strength

*φ*Friction angle

## Notes

### Acknowledgements

This work is supported by the National Natural Science Foundation of China (Nos. 41472245; 41672300) and the Opening Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (SKLGP2017K015).

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