Iowa Department of Transportation
Sri Sritharansri@iastate.edu email >
Faculty Affiliate, BEC
Jeramy Ashlockjashlock@iastate.edu email >
Faculty Affiliate, InTrans
About the research
In the state of Iowa, the use of drilled shafts to support highway bridges have significantly increased over the recent years. In certain ground and construction site conditions, drilled shafts have been shown to be more advantageous and cost effective compared to the driven piles commonly used by the Iowa Department of Transportation (DOT). Drilled shafts can carry much higher axial and lateral loads while eliminating the need for pile caps.
Current design guidelines and details in the Iowa Bridge Design Manual for the LRFD design and construction of drilled shafts rely heavily on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications. Although these specifications have allowed the Iowa DOT Office of Bridges and Structures to design all bridges in accordance with the FHWA mandate to use the LRFD approach on all federally-funded bridges initiated after October 1, 2007, the resistance factors currently recommended by AASHTO for drilled shaft design suffer from a few limitations. And the AASHTO specifications were not specifically developed for the state of Iowa, thus they do not reflect local soil conditions and construction practices. Because of the significant effects that local ground conditions and construction techniques can have on the accuracy of estimates of drilled shafts field performance, it is of paramount importance to establish resistance factors at regional levels utilizing a local high-quality load test database.
This project focuses on participating in upcoming drilled shaft load tests and collecting additional data in order to provide final resistance factor recommendations and to develop an in-house drilled shaft design method with its corresponding resistance factors, as suggested by Iowa DOT. The development of the new method will emphasize intermediate geomaterials and rock, as they are the primary soil conditions where Iowa DOT uses drilled shafts.