One interesting and important portion of this article for geotechnical practitioners was discussion of the changes to the AASHTO code for the 2007 National Subcommittee vote. A working group comprised of FHWA representatives and drilled shaft industry representatives has been working with the AASHTO Subcommittee on Bridges and Structures on a comprehensive review and update of Section 5 of the 2006 AASHTO LRFD Bridge Construction Specifications for drilled shafts. The same committee will also be evaluating the current FHWA drilled shaft design and construction guideline specification. According to Mr. Nichols, the "hot topics" in the specification include:
- An evaluation of drilled shaft concrete mix designs (including self consolidating concrete) for mass pours associated with deep, large diameter shafts.
- Updating bentonite, blended and polymer slurry specification guidance.
- Providing a clear definition of obstructions and a protocol dealing with them
- Providding clear guidance on the definition of top of rock.
- Providing better guidance for the use of non-destructive testing and a protocol for coring of questionable shafts. The specification review will also address shaft remediation and repair protocols.
Also discussed in the article was a recent contract awarded by the FHWA to begin work on a third update to their drilled shaft design and construction manual and the corresponding NHI course. Practicing geotechnical engineers will be familiar with the Reese and O’Neil 1999 version, which is essentially the Bible for drilled shafts. The new version and the training course is expected to be released in 2008.
As reported on his website, Dan Brown, PhD, PE will be leading the technical team. The contract administrator is Parsons Brinkerhoff (PB) with Jeremy Hung, PE as the PB Project Manager.