How is standard penetration test carried out?

A Standard Penetration Test (SPT) is conducted by driving a split-barrel sampler into the ground at predetermined intervals, typically using a hammer weighing 140 pounds dropped from a height of 30 inches. The sampler is driven into the soil until it reaches a depth of 18 inches, and the number of hammer blows required to penetrate the last 12 inches is recorded as the SPT N-value. This value provides an indication of the soil's density and strength, which is critical for geotechnical engineering applications. The test is often performed at various depths to assess soil properties at different strata.