A cut slope is to be made in a clayey soil to permit construction of a new highway as shown below. A slope stability analysis is to be performed along the potential shear surface shown in the figure. The soils are silty clays with c' = 18 kPa, phi’ = 20degree. If the shear stress at point A is 60 kPa, compute the factor of safety against sliding at A.

The factor of safety against wedge failure along interface for the soil mass along with properties shown below is Weight of wedge ABC = 70 kN; C = 8 kN/m²; + = 20° 3 m T H Soil mass 5.8 m B 2.5 m

Problem 1Explain whether the following are true or false. 1. A lower safety factor implies that a greater fraction of the shear strength is mobilized along the failure surface. 2. In an undrained slope of 1.0 (horizontal): 1.5 (vertical), the critical circle is always a toe circle. 3. The mid-point circle passes through the toe. 4. Taylor’s stability charts can be used only for homogeneous soils.

A cut slope in soft clay has been constructed as part of a road alignment. The slope is 21.8 degrees and 10 m high. The unit weight of the soft clay is 18kN/m3. (i) A walk over survey recently indicated signs of instability. Samples have been collected from the slope and the drained analysis parameters for the soil have been determined as follows: Soil properties: φ'= 24 º, c'=2.5kPa, γd=19kN/m3 , γsat=20kN/m3 Based on the effective stress parameters given, perform a quick initial estimate of the factor of safety of this slope using Bishop and Morgernsterns charts. Assume an average pore water pressure ratio (ru) of 0.3 for the slope