Because of the large load capacity of drilled shaft foundations, it is relatively difficult and expensive to conduct full scale load tests. As a result, the bearing cacpacity of drilled shafts in rock has traditionally been assessed very conservatively. The results of this research project allowed greater bearing values to be used, making drilled shafts more economically designed and constructed.
The issue of how far and in what manner concrete can be placed by the free-fall method in drilled shafts under dry conditions has long been of great interest to our industry. In the early 1960s, Clyde Baker and John Gnaedinger of STS Consultants produced a study that concluded that the acceptable limit was over 90 feet. Since this result was not universally accepted, in 1994 the ADSC and STS Consultants, with support from the FHWA, designed and conducted a comprehensive field test that has effectively settled the question.
The report stated: We conclude that the free-fall placement method of concrete into properly constructed clean and dry shafts can be performed to depths of 120 feet or greater without meaningful loss of strength or segregation of the concrete aggregate.
Adoption of this report in the industry, under the auspices of the FHWA, has greatly enhanced the constructability of drilled shaft foundations. Many drilled shaft contractors consider this report the first notable research achievement of the Industry Advancement Fund.
Rock Sockets in Southeastern U.S.
Micropile AASHTO LRFD Calibration (and Spec Development)
Moving a new technology into the mainstream requires building consensus and developing common design guidelines. IAF was instrumental in this regard for micropiles. The initial project, with IAF support, developed micropile calibration studies in conformance with AASHTO LRFD procedures. With this calibration in hand, the ADSC Micropile Committee could develop and revise the initial draft of the AASHTO design specification and usher it through the AASHTO acceptance process. Finally, working jointly with the DFI, the Micropile Committee developed a construction specification that was recently accepted into the AASHTO highway code. A tremendous effort here—and it all started with a grant from the IAF.