The Standard Penetration Test (ASTM 1586) is the use of a cast metal sampler that is 2-inches in diameter which is split vertically and secured at the base of the sampling rods at top and bottom by a rod adapter and shoe respectively. The sampler is lowered into an open excavation, onto relatively undisturbed, in-situ soil, and is hammered into the ground by a 140 lb hammer on a 30-inch free-fall drop. The number of blows from the hammer required to drive the sampler is recorded in 6-inch intervals. If more than 50 blows are administered in any 6-inch increment the sampling stops. Otherwise, the sum of the 2nd and 3rd increment blow-counts is recorded as the “N”-value. This is used to estimate numerous soil properties based on correlations developed by engineers over many years.
