Evaluation of pile bearing capacity by dynamic tests

Conclusions

1. In determining the bearing capacity of piles, dynamic resistance should be understood to mean that maximum value of soil reaction which is generated during the hammer blow. However, this concept should not be confused with the resistance obtained from the results of dynamic pile tests.

2. Upon the delivery of a dynamic blow, as pile penetration proceeds, an increase in soil reaction occurs which reaches the limiting and then the critical load values as obtained from static tests. Therefore, the results of dynamic tests if the latter are correctly performed should coincide with the critical load obtained from static tests. Experience has shown that for this condition to be fulfilled, the total refusal of piles due to a single blow should be not less than 10–15 mm and the residual part of the refusal should be not less than 2 mm.

3. The results of the dynamic tests enable the static pile resistance to be determined for the soil condition at the given instant. As is shown by graphs of the dynamic and static tests, the limiting pile resistance depends not on the type of test but on the condition of the soil and the degree of its thixotropic recovery.

4. The determination of pile bearing capacity by the dynamic method, taking their "resting" into account, should be based on the results of the initial blows.