(Solved): Question 2: Factor of Safety Analysis for Circular Arc Failure [60 pts] The design of a 15 m high so ...

Question 2: Factor of Safety Analysis for Circular Arc Failure [60 pts] The design of a 15 m high soil slope (in Figure 1) must incorporate a susceptible circular arc failure. The slope is inclined at \( 45^{\circ} \) angle. Detailed soil tests, mapping and sample analysis show that the soil cohesion is \( 25 \mathrm{kN} / \mathrm{m}^{2}(\mathrm{KPa}) \) and the friction angle is \( 35^{\circ} \). The unit weight of formation, \( \mathrm{W}_{\mathrm{s}}=22 \mathrm{kN} / \mathrm{m}^{3} \) and that for water, \( \mathrm{W}_{\mathrm{w}}=9.81 \) \( \mathrm{kN} / \mathrm{m}^{3} \). Safety factor analysis is to be carried out using 5 slices as illustrated in Figure 1. Hint: In your volume calculations, use section thickness of 1 m . (a) Use method of slices to estimate slope factor of safety when it is (i) totally dry and (ii) fully saturated. (c) What practical steps can be taken to ensure slope safety under these conditions? (b) Examine the factor of safety using Hoek's preliminary design charts for totally dry and fully saturated conditions and compare the answers in (a) and (b). Figure 1: Circular Arc Failure Analysis by Method of Slices