Standard Penetration Test

Standard penetration test (SPT) is a widely used in-situ test. This test is governed by EN ISO 22476 part 3 for United Kingdom and European region, and ASTM D1586 for the United States.

Prior to the test, a borehole is drilled to the desired test depth. SPT sampler is then lowered to the borehole. The test is conducted by driving the sampler into the ground using drop hammer. Initial seating drive of 150mm is required. Subsequently, total 300mm of test drive is performed, and the number of blows for each increment (either 150mm or 75mm) is recorded. The test may be terminated once the total blow count reaches 50. If the test is not terminated in this manner, total number of blows for 300mm test drive is calculated by summing the blowcount for all increments.

The N value obtained from SPT needs to be corrected to reference energy ratio of 60%, based on rod length, borehole diameter and the energy ratio commonly used for the test region. The corrected value may then be normalized based on overburden pressure.

Data from SPT can be used to calculate the bearing capacity of shallow and deep foundation.