Civil Engineering Association

DRILLED SHAFT FOUNDATION DEFECTS-Identification, Imaging, and Characterization

This study was conducted under the Federal Highway Administration (FHWA), Central Federal
Lands Highway Division (CFLHD) contract number DTFH68-03-P-00116. The current practice
in assessing the integrity of newly constructed drilled shaft foundations, or other concrete
structures that contain access tubes, is through the use of nondestructive testing (NDT) methods.
Most common NDT methods include crosshole sonic logging (CSL), gamma-gamma density
logging (GDL), and crosshole sonic logging tomography (CSLT). Numerous studies and field
investigations have been performed to evaluate the accuracy and effectiveness of these NDT
methods in detecting defects in drilled shafts. However, most of these studies have fallen short
to correctly identify and characterize defects for engineering decision making. Or, as stated by
Jerry DiMaggio (2004), FHWA Principal Geotechnical Engineer, “when using (NDT) methods,
the key questions that often must be answered are: (1) Is the test result a false negative? (2)
What are the next steps and who is responsible for incurred cost if a defect is suspected? and
most importantly (3) Is the discontinuity a defect?”