Dynamic testing of very short foundation elements can pose difficulties due to measurement inaccuracies and possible violation of the slender rod assumption in the theory. The guidelines below are the recommended minimum lengths:
- The total length of the foundation element to be tested should not be less than five times its diameter, so that the sensors can be installed a distance equivalent to two diameters below the top, and there is still at least three diameters left below the sensors.
- The length below gages should not be less than 2 m (6.6 ft).
- If the foundation element to be tested does not meet the criteria above, building or adding an extension and/or testing a longer pile on the same job should be considered. Testing of piles shorter than the recommendations above is still possible, however, if there is no way of extending the pile length.
It is also recommended that the number of pile and soil elements in CAPWAP is increased to at least 4 for length below sensors (LE) between 2 and 4 m (6.6 and 13 ft). Also, the maximum PDA sampling frequency of 20 kHz should be used for piles with lengths below sensors (LE) of less than 5 m (15 ft).Return to FAQs