Class-A Prediction of Construction Defects in Drilled Shafts

The results of a blind Class-A prediction symposium of construction defects in drilled shafts are presented. Six drilled shafts were constructed at the National Geotechnical Experimentation Site in Amherst, Massachusetts. Several types of defects were integrated into the shafts, including necking, voids, caving, and soft bottoms. Seven organizations participated in a blind defect prediction symposium and used a variety of nondestructive testing techniques, including down-hole techniques, such as cross-hole sonic logging, single-hole sonic logging, and cross-hole tomography, and surface techniques, such as pulse echo and sonic mobility. Most participants found defects that were larger than 10 percent of the cross-sectional area. However, false positives and an inability to locate smaller defects and multiple defects in the same shaft were encountered.