Soil borings for the subsurface investigation of a site indicate a deep deposit of sandy soils. At one boring location, the blow count logged for the standard penetration test, N 60 , while sampling...

Soil borings for the subsurface investigation of a site indicate a deep deposit of sandy soils. At one boring location, the blow count logged for the standard penetration test, N₆₀, while sampling at a depth of 25 feet was 22 blows/ft. The sand has a unit weight of 115 pcf. Using criteria that relate SPT results and the soil angle of internal friction, estimate the value of f for the sand at the sample depth.