The use of drilled shaft foundations has been increasing. A reason for this growth is the ability to routinely test drilled shafts by using nondestructive testing (NDT) methods. Several NDT techniques are widely used, including cross-hole sonic logging (CSL), pulse echo testing, and sonic mobility. These techniques help owners and engineers confirm that drilled shafts are unimpaired by construction defects. This is important for two reasons. First, drilled shaft foundations lack the redundancy of driven pile foundations, which typically use a larger number of lower-capacity piles. Second, in the United States, drilled shafts often are constructed with the aid of polymer or bentonite slurry to keep the hole open, instead of with full-depth casing used in other parts of the world. This technique does not allow for easy inspection of the integrity of the shaft before and during concrete placement.
Shaft Dimensions |
Project Layout |
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An effort to further study the accuracy of the NDT techniques commonly used by the consulting community and state highway departments was organized in the form of a blind Class-A prediction symposium. This effort took place as a full-scale field test conducted at the National Geotechnical Experimentation Site (NGES) in Massachusetts, Amherst, in March and April 2000.
Six drilled shafts were constructed, some with built-in defects, for this project. Static and Statnamic load tests also were performed on these shafts in July 2000 to investigate the effect of defects on the axial capacity of drilled shafts. Leading NDT testing firms and universities were invited to participate, and seven organizations took part in the program. This website presents the results of this effort.
Built in Defects |
NDT Access Tubes |
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Construction Defects |
Shaft Dimensions |
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