Articulo Aguas Residuales

Modeling of suction distributions in an unsaturated heterogeneous residual soil slope

Azman Kassim a, Nurly Gofar a,⁎, Lee Min Lee b, Harianto Rahardjo c

a Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai 81300, Malaysia

b Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Kuala Lumpur 53300, Malaysia

c School of Civil and Environmental Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 2263, Singapore

a r t i c l e i n f o a b s t r a c t

Article history:

Received 26 June 2011

Received in revised form 31 January 2012

Accepted 3 February 2012

Available online 14 February 2012

Keywords:

Suction distributions

Soil heterogeneity

Relict discontinuity

Residual soil

Slope stability

The formation of residual soil of Grade V and Grade VI due to tropical weathering process introduces small

hydraulic heterogeneities in the soil mantle which greatly alter the suction distribution during rainfall infiltration,

and hence the stability of the residual soil slopes. This paper presents field evidences of suction distributions

in a heterogeneous residual soil slope. Several modeling approaches were attempted to simulate

the observation by considering the presence of thin layer of Grade VI, the variation in the hydraulic conductivity

of Grade V layer as well as the effect of evaporation. The soil hydraulic heterogeneity in Grade V layer

was modeled by adopting continuum method, in which the residual soil was subdivided into three zones of

average hydraulic conductivities. The analysis results show that the presence of thin layer of Grade VI residual

soil and the relict discontinuities in Grade V soil must be considered in the analysis as these features introduced

permeability disparity and thus a natural capillary barrier effect that limited the downward

movement of infiltrated rainwater even during the exceptionally wet condition. The results also show that

the inclusion of evaporation effect provided a better prediction to the suction distributions during wet condition

than dry condition.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Rainfall-induced slope failure is a common geohazard in many

parts of the world, particularly in tropical regions which are covered

extensively with residual soils (Brand, 1984; Shaw-Shong, 2004;

Huat et al., 2005; Rahardjo et al., 2005; Rahimi et al., 2010). These

slope failures are commonly shallow with typical depth of slip surface

of 1 to 3 m oriented parallel along the slope surface (Muller and

Martel, 2000; Kim et al., 2004; Matsushi et al., 2006). The failures

are mainly attributed to the total or partial loss of matric suction during

rainfall infiltration, and hence cause a reduction in shear strength

of soil, with not much evidence on the rise of groundwater table

(Fredlund and Rahardjo, 1993; Fourie

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