Abstract
Rainfall-induced slope failure is a common natural disaster that occurs frequently in many parts of the world. Many studies have been conducted on the effect of advancement of wetting front on reduction or elimination of the additional shear strength provided by matric suction in unsaturated soil. However, the inclusion of boundary flux condition such as evaporation in predicting soil suction for rainfall-induced slope failure analyses is still limited. Therefore, this study investigate the combined effect of two boundary flux (infiltration and evaporation) on transient suction distribution and hence the factor of safety (FOS) of a modelled slope which consist of slope height and horizontal distance of 5 and 47 m respectively with a slope angle of 21°. One year rainfall and evaporation data of a site in Johor Bahru, Malaysia were collected for the study and two months were selected to represent the wet and dry seasons based on the two predominant wind systems which brings rainfall in Malaysia (Northeast and Southwest monsoons). Soil samples were collected from the site for laboratory testing and the relevant soil properties required in the analyses were obtained. Initial soil condition was determined from Soil Water Characteristics Curve (SWCC) of the soil sample from the study area and these initial conditions were simulated at the beginning of each analysis to enable realistic condition of the soil to be obtained. The seepage analyses were conducted with Seep/w and the pore water pressure determined from the seepage analyses were used as input parameters in the slope stability analyses carried out with slope/w. The results of the analyses show that considering flux boundary condition has a great influence in maintaining negative pore water pressure in unsaturated soil especially during wet period when there is more water infiltrating the soil. Moreover, inclusion of evaporation in seepage analyses give more realistic pore water pressure and hence better prediction of FOS of the slope. Keywords: Evaporation, Flux Boundary, Rainfall, Slope Stability, Suction Distribution
Highlights
Slope instability due to rainfall infiltration is one of the aspects of Geotechnical engineering that receives much attention over the past decades
In tropical regions; water table exists at great depth and the soil above the water table typically exist in unsaturated condition, ; mostly these types of failure do not occur due to rise in water table rather it resulted from the
The rainfall and evaporation data were obtained from the Department of Irrigation and Drainage (DID) Malaysia and it covers a period between January to December, 2009, among these data two months were eventually selected for the analyses; one month representing the wet period and the other month representing the dry period
Summary
Slope instability due to rainfall infiltration is one of the aspects of Geotechnical engineering that receives much attention over the past decades. It is a common and frequent natural disaster in many parts of the world tropical climate countries experiencing period of intense or prolonged rainfall events[1,2,3,4,5,6,7]. Apart from hydraulic properties of soils; the variation of negative pore-water pressure (suction) in unsaturated soils is affected by climatic conditions such as rainfall characteristics (intensity and duration), rainfall pattern, evaporation and evapo-transpiration[18]. Accurate prediction of evaporation has great application in predicting the pore-water pressure in the soil profiles for slope stability analysis[19]
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