| Summary: | A landslide in residual soil normally occurs immediately after heavy rainfall. Previous studies have shown that decrease in matric suction during rainfall decreases the shear strength of soil and results in landslides. One of the factors that contribute to infiltration of water into soil is permeability of the soil which varies with depth. The variations of permeability can either prevent or allow water to infiltrate into deeper soil layer. Therefore, the aim of this study is to determine the suction distribution in a two-layered residual soil system with variable permeability function using laboratory physical slope model. The Ksat for Grade V varies from 5.11 × 10-4 m/s for relict joint of 100 mm spacing to 5.40 × 10-5 m/s for relict joint of 300 mm spacing. Meanwhile the Ksat for Grade VI represent Grade VI without burrow holes, 5.00 × 10-7 m/s and Ksat with burrow holes, 6.98 × 10-4 m/s. The infiltration tests were conducted for 12 series of experimental program. The suction distribution due to variations of permeability and rainfall intensity were determined. The results illustrated that suction distribution responded in various ways depending on permeability of the layered soil and also the rainfall intensity.
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