(Solved): b Question 5-Slope Stability (25 Marks) (a) A natural slope inclined at 1:4 is to be cut in weathe ...

b Question 5-Slope Stability (25 Marks) (a) A natural slope inclined at 1:4 is to be cut in weathered material and therefore necessitates some stability analysis. The soil profile of the slope in the weathered material has a depth of 3 m, and below which is un-weathered rock. Direct shear tests carried out gave the following soil parameters c' = 10 kPa and '= 30°. The unit weight of the dry soil is 16 kN/m³ and it increases to 20 kN/m³ when it becomes saturated. Take the unit weight of water is 10 kN/m³. Determine the factor of safety against shear failure on the soil-rock interface when: (i) the soil is dry and (ii) the soil is completely submerged with seepage parallel to the slope. [5 marks] [5 marks] (b) A slope is to be excavated at an angle of 30° to a height of 10 m. The soil is a saturated clay with the following soil parameters: Cu = 35 kPa and y = 18 kN/m³. A hard stratum is at is located at depth of 15 m. (i) Determine the FS against slope failure and the position of the most critical sliding surface. [5 marks] (ii) What is the maximum slope angle that the clay will be able to sustain? (5 marks] (iii) Give a sketch of the configuration of the slope providing the angle at the centre of [5 marks] rotation.