Developing a Resistance Factor for Mn/DOT's Pile Driving Formula

Status:  Complete
Report Date:  12/03/2009


Driven piles are the most common foundation solution used in bridge construction across the U.S. Their use is challenged by the ability to reliably verify the capacity and the integrity of the installed element in the ground. Dynamic analyses of driven piles are methods attempting to obtain the static capacity of a pile, utilizing its behavior during driving. Dynamic equations (a.k.a. pile driving formulas) are the earliest and simplest forms of dynamic analyses. Mn/DOT uses its own pile driving formula; however, its validity and accuracy has not been evaluated. With the implementation of Load Resistance Factor Design (LRFD) in Minnesota in 2005, and its mandated use by the Federal Highway Administration (FHWA) in 2007, the resistance factor associated with the use of the Mn/DOT driving formula needed to be calibrated and established. The resistance factor was established via the following steps: (i) establishing the Mn/DOT foundation design and construction state of practice, (ii) assembling large datasets of tested deep foundations that match the state of practice established in the foregoing stage, (iii) establishing the uncertainty of the investigated equation utilizing the bias, being the ratio of the measured to calculated pile capacities for the database case histories, (v) calculating the LRFD resistance factor utilizing the method's uncertainty established in step (iv) given load distribution and target reliability. The research was expanded to include four additional dynamic formulas and the development of an alternative dynamic formula tailored for the Mn/DOT practices.

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