 |
 |
 |
 |
This web site presents the results of nondestructive integrity tests and axial static load tests on drilled shafts constructed in varved clay at the National Geotechnical Experimentation Site, which previously existed at Amherst, Massachusetts. 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.
The work has been sponsored by the Deep Foundations Committee of the Geo-Institute of ASCE, The Federal Highway Administration, and The International Association of Foundation Drilling.
Primary References
- Iskander, M., Roy, D., Kelley, S., and Ealy, C. (2003). ”Drilled Shaft Defects: Detection, and Effects on Capacity in Varved Clay.” Journal of Geotechnical and Geoenvironmental Engineeering, 129(12), 1128–1137 [link]
- Iskander, M., D. Roy, C. Ealy, and S. Kelley, (2001). “Class-A Prediction of Construction Defects in Drilled Shafts,” Journal of Transportation Research Board, No. 1772, pp. 73-83, National Academy Press [link]
