The Ball-CPT survey consists of the sinking and withdrawal of a spherical (Ball) penetrometer which incorporates a sensor for measuring pore pressure, u. Soil resistance can be recorded both during the static sink process and the inverse extraction phase.

 

The possibility of obtaining results both in the initial monotonic penetration phase and from cyclical surveys, makes the Ball survey particularly useful for determining su, the undrained shear resistance of undisturbed soils, and sur, the shear resistance of remoulded soils, and thus the sensitivity. It is applicable to both cohesive and fine granular soils.

The capacity to test the response of soil subjected to cyclical loads allows the measurement of the degradation of the ground subjected to these cycles and is directly applicable to liquefaction analysis.

 

Advantages

The basic advantage of this survey compared to the traditional CPTU survey is that during penetration by the Ball-CPT, the soil is not disturbed which allows measurement of the ground which flows around the penetrometer. In view of this, many of the corrections for overpressure and pore pressure which are applied in CPTU surveys are unnecessary.