Citation

Walpita SC, Ratnaweera P, Fernando GWAR. J. Natl. Sci. Found. Sri Lanka 2022; 50(2): e405.

Copyright

(Copyright © 2022, National Science Foundation of Sri Lanka)

DOI

10.4038/jnsfsr.v50i2.10290

PMID

unavailable

Abstract

In the event of a rainfall, the contrast in hydraulic conductivity and shear strength properties of layered soil can be significant in determining the stability of a slope. The main objectives of this study were to model 1-D infiltration into a two-layered soil formation and to understand the effect of contrast in the permeability characteristics of the two layers on failure depth, time, and mechanism, in the event of a shallow landslide. Two hypothetical soils-relatively coarse and fine soils-were assumed for the layered soil model. 1-D infiltration into partially saturated soil has been modelled through the development of a finite difference numerical scheme by solving the mixed form of Richard's equation. The stability analysis has been conducted for varying rainfall intensities and permeabilities using a pre-defined stability envelope based on the pressure head. For the case where fine soil overlies the coarse soil in a two-layered model, results showed that the failure depth is significantly reduced when the saturated permeability of coarse soil decreases relative to the fine soil. The only possible failure mechanism was identified as 'loss of suction'. When the coarse soil overlies a fine soil, no significant effect on failure depth has been observed. Both 'loss of suction' and the development of a 'perched water table' were identified as possible mechanisms. In both cases, it was noticed that the failure time decreases as the saturated permeability of coarse soil increases. The results suggest that contrast in permeability characteristics in layered soil formations plays a vital role in influencing failure time, depth, and mechanism.

Language: en