Drilled shaft defects: Detection, and effects on capacity in varved clay

Magued Iskander, Douglas Roy, Shawn Kelley, Carl Ealy

Research output: Contribution to journalArticlepeer-review


This paper presents the results of nondestructive integrity tests (NDTs) and axial static load tests on drilled shafts constructed in varved clay at the National Geotechnical Experimentation Site in Amherst, Mass. The shafts were constructed with built-in defects to study: (1) the effectiveness of conventional NDT methods in detecting construction defects and (2) the effect of defects on the capacity of drilled shafts. Defects included voids and soil inclusions occupying 5-45% of the cross section as well as a soft bottom. Nine organizations participated in a blind defect prediction symposium, using a variety of NDT techniques. Most participants located defects that were larger than 10% of the cross sectional area. However, false positives and inability to locate smaller defects and multiple defects in the same shaft were encountered. Static load tests indicated that (1) minor defects had little or no effect on skin friction: (2) a soft bottom resulted in a 33% reduction in end bearing relative to a sound bottom; and (3) reloading resulted in a 20-30% reduction in the geotechnical capacity.

Original languageEnglish (US)
Pages (from-to)1128-1137
Number of pages10
JournalJournal of Geotechnical and Geoenvironmental Engineering
Issue number12
StatePublished - Dec 2003


  • Clays
  • Defects
  • Drilled shafts
  • Nondestructive tests
  • Static loads

ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology
  • General Environmental Science


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