Poster 19-06

LRFD Procedure for Piles with Pilot Hole in Rock


PI: Soonkie Nam

Co-PI(s): Xiaoming Yang

Institution(s): Georgia Southern University


Abstract

In Georgia, when a hard/dense layer exists in the pile length or the vibration/noise during the driving causes secondary issues, a pilot hole is often adopted as a pile-driving assistance method to aid driving displacement piles through, especially if a competent hard rock layer exists in a reasonable depth. The use of a pilot hole reduces construction time and uncertainties related to driving through the problematic layers. However, the pilot hole is considered different from a pre-drilled hole in terms of construction method and design assumption. This process also complicates the prediction of long-term pile capacity with a predrilled hole. An objective of this study was to identify and document the current guidelines available and adopted by different states, and investigate the relationship between the load capacity of piles installed in rock and their design parameters with respect to the pilot hole, rock conditions, and installation method. Another objective was to identify a reliable design procedure that incorporates proper LRFD resistance factors, and a field verification method for quality assurance of rock. It is found that pile driving analyzer (PDA) can be applied to the piles with a pilot hole on rock and verify the structural capacity of the pile if not the geotechnical capacity due to the higher bearing capacity on rock. It also can check the internal stress to avoid the damage during striking. Thus, the study recommends the use of PDA tests and the AASHTO resistance factor for driven piles with dynamic testing, while collecting the strength properties of the rock mass. The driving refusal criterion can be used when the rock condition is evident. However, it is still recommended that the correlations between the refusal guidelines and rock properties are verified with PDA.


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