A retaining wall, 8m high with a smooth vertical back, retains a clay backfill with C'= 15 kN/m2, Φ' = 15° and γ = 18 kN/m3. Assume that the tension cracks may develop to the full theoretical depth, the active thrust on the wall is
1
23 kN/m2
2
20 kN/m2
3
46 kN/m2
4
61.67 kN/m2