A site consists of 100 ft of sand (t = 120 pcf) underlain by hard clay. The groundwater table is found 10 ft below the

A site consists of 100 ft of sand (γt = 120 pcf) underlain by hard clay. The groundwater table is found 10 ft below the ground surface. Standard penetration blow counts (N) have been measured at the site and they are around 10. Estimate the effective friction angle for the sand (assume c’ = 0). Calculate the sand’s shear strength on a horizontal plane at depths of the 20 ft and 50 ft.