Pile testing

Alongside cone penetration tests and core sampling, pile penetration testing is an alternative method for building ground investigation. In pile penetration testing, the resistance of the soil to the dynamic penetration of a probe tip is determined.

In pile penetration testing, a probe tip fitted with a drop weight – also known as a pile block – which has a standardised weight and a standardised drop height, is driven into the ground. The number of blows required to achieve a penetration of 10 cm is counted and recorded. Recording takes place continuously as the probe penetrates deeper. At the end of the test, the documentation of the number of blows required provides information, depending on the soil type, about the density and bearing capacity of the soil. In practice, depending on the expected resistance and the grain diameter of the soil, light (DPL), medium (DPM) and heavy (DPH) pile driving tests are commonly used.

Pile driving tests are standardised in accordance with DIN EN ISO 22476-2:2005.

Advantages and disadvantages of the pile penetration test

Whilst pile penetration tests are simple to carry out, their value as an investigative method is limited to a small number of soil types, and they have the disadvantage that no soil samples can be taken.

Penetration testing in non-cohesive soil types

In the case of non-cohesive soil types, i.e. sandy and gravelly soils, conclusions can be drawn regarding the density of the soil based on the number of blows required per 10 cm. For example, the density of a sandy soil requiring 10 blows when using the light pile probe can be assessed as average, which corresponds to a good foundation soil.

Penetration testing in cohesive soil types

Whilst for non-cohesive soil types the number of strokes provides a good indication of the density and thus the bearing capacity of the soil, this applies to cohesive soil types only to a limited extent and requires experience gained on site.