Non-destructive evaluation of drilled shafts at the Amherst NGES test section

Impulse response tests were conducted on the drilled shafts at the Amherst National Geotechnical Experimentation Site (NGES) as part of a prediction symposium. The nominally 14-m-long drilled shafts were constructed with anomalies, the nature and number of which were unknown when the impulse response tests were conducted and the analyses made. The planned anomalies included necking, voids, caving and soft bottoms. The predictions were based on conventional sonic echo and mobility plots, and comparisons with numerical simulations. The conditions at the test site are summarized, and comparisons between the predicted and as-built anomalies are presented. The rationale with which the predictions were made and the limitations of such predictions are discussed. Reasonable agreement between the predicted and actual anomalies was obtained within the upper half of the shaft, but poor agreement was found in the lower half of the shaft. After the non-destructive testing was completed, axial load tests were conducted on the shafts. These load test results are discussed in light of whether these anomalies could be considered "defects," i.e., anomalies that are sufficiently large as to impact the axial load capacity of the piles.