The Subjective Element in Dynamic Load Testing Results

Dynamic Load Testing (or High Strain Dynamic Testing as the test is called in the ASTM Standard D4945) is widely considered as a reliable method to determine the capacity of deep foundation elements. To illustrate the reliability of this test method, comparisons between the outcome of a Dynamic Load Test and a Static Load Test on the same pile are often used in the literature, which seem to confirm that the outcome of a Dynamic Load Test can accurately predict the capacity. However, these illustrations generally ignore the subjective aspect of the test result interpretation because, when this aspect is included, a completely different view on the method's reliability emerges. This paper will use the results of the various international prediction events to illustrate this aspect, which will clearly demonstrate that the reliability of this test method should be reassessed where it has not been adequately validated by adequate site characterization and static load testing. The paper will finally address the impact of this re-assessment on the resistance factors that have been derived solely from Dynamic Load Test results.