4. (a) A 40 m high residual soil slope with a slope angle of 60 degrees has a horizontal ground water table at a depth o

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4 A A 40 M High Residual Soil Slope With A Slope Angle Of 60 Degrees Has A Horizontal Ground Water Table At A Depth O 1 (69.02 KiB) Viewed 20 times

4. (a) A 40 m high residual soil slope with a slope angle of 60 degrees has a horizontal ground water table at a depth of 20 m below the toe of the slope. At the end of a continuous rainfall of 10 mm/h for 16 hours, the slope experienced a landslide. The geotechnical investigation indicated that the rainfall-induced landslide was a shallow slide with an almost uniform depth slip surface of around 1.3 m. (0) Briefly explain the role of rainfall in causing the landslide, using principles of stress state variables. (5 Marks) (ii) Describe the procedure required to analyze the effect of rainfall on stability of the slope using the extended Mohr-Coulomb shear strength method. Please explain clearly the saturated and unsaturated soil properties required for the analyses. Use sketches if necessary. (10 Marks)