For a clay slope of height 20 m, the stability number is 0.05, y = 25 kN/m³, and c = 30 kN/m², the critical height of slope is: 1, 30 m 2, 20 m 3. 24 m 4. 26 m

Please answer (a)

A thin clay layer passes through the soil at an angle of 30° behind an 8m high gravity retaining wall. A structure 5m wide, applying a uniform stress of 40kPa to the sandy soil, also acts on this section of soil as shown in Figure 3.1. The properties of the clay are ??=25???, ∅?=0, ?′=0 and ∅′=20°. The sandy soil properties are ?′=0, ∅′=35°, ????=16??/?2, ????=20??/?2, and between the sand and the wall the properties are ?′?=0 and ∅′?=30°. Assuming that failure occurs along the clay layer, use Coulomb’s method to calculate the horizontal force required from the wall in the short term to prevent slip.