Low strain (small strain) method can be used to detect small diameter piles.
For large diameter piles, other methods such as drilling core method (more expensive to detect) and so on can be used.
In conditional engineering, other methods such as drilling and coring can be used to test pile length.
According to the code, low strain is to measure the integrity of the pile, not the length and strength of the pile. The error of pile length is about 1m, and a difference of one or two meters cannot be measured.
If the pile length is less than 20m, it is more accurate. The calculation method is: L = V*t, that is, the length is equal to the pile bottom wave velocity velocity times time.
The accuracy of pile length detection can be improved as long as the operation is standardized, the dry factors of field testing are excluded as far as possible, and some signal data processing methods are adopted.