How does a penetrometer work?
Penetrometers are measuring devices for determining the penetration resistance in the soil. The penetration measurement is based on early soil assessment methods, with a walking stick pressed into the ground. A comparison of the force required for this purpose revealed the composition and condition of the soil. This method, however, was highly subjective and allowed only a comparison by one and the same person. Modern penetrometers therefore detect the force (in Kg or N), which is effective during the piercing operation, with force sensors. By reference to a defined area, a pressure (in Kg/cm²) is obtained. This area results from the base area of the penetrating tip of the penetrometer (penetrometer cone). The base area of the standard cone for penetration measurements on soils in Germany is 1 cm². The cone is generally replaceable, since it wears itself by the friction during the piercing, whereby the reference surface (base area of the cone) is undefined. In addition, you can change between cones of different base areas. This allows adaptation to different measuring conditions.
In compliance with the application, penetrometers are available in a wide variety of designs. The force can be displayed on manually readable scales or digitally. Penetrologgers can record the course of the force over the entire insertion depth. Pocketpenetrometers offer a small, easy-to-carry possibility to make statements about the penetration resistance of a soil.
A prerequisite for the recording of a correct depth profile of the penetration resistance is a uniform propulsion of the penetrometer into the ground. Depending on the prevailing soil conditions and the physical conditions of the executive person, this is often very difficult to achieve manually. Penetrometers with automatic advancement guarantee a uniform penetration speed and thus comparable measured values.
In addition to compaction of the soil, the soil moisture has a considerable influence on the penetration resistance. Therefore, innovative penetrometer systems also also capture the water content of the soil.