3. (a) Calculate the total active thrust on a vertical wall 5m high retaining a sand of unit weight 17 kN/m³ for which f' = 35°. The surface of the sand is horizontal and the water table is below the bottom of the wall. (b) Determine the thrust on the wall if the water table rises to a level 2m below the surface of the sand. The saturated unit weight of the sand is 20 kN/m³. (20 marks) Page 4 of 4 E. M. BUABA