Reliability-based design improvement and prediction of steel driven pile resistances in rock-based intermediate geomaterials.

Driven piles are considered to be an excellent deep foundation design choice due to the economic benefits and availability. However, there is a knowledge gap in assessing pile driving and predicting pile resistance in rock-based intermediate geomaterials (R-IGMs). A better prediction of pile resistances, anticipated refusal depth and pile design methods are essential to alleviate current challenges with piles driven in R-IGMs. This paper presents recommendations for piles driven in weak rocks or R-IGMs based on 39 test piles from 28 bridge projects completed in three US states. Static analysis (SA) methods for predicting unit shaft resistance (qs) are developed based on in situ SPT N-value and unconfined compressive strength (qu) for five different weak rocks: siltstone, claystone, sandstone, mudstone and granite. SA methods for predicting unit end bearing (qb) are developed for siltstone and claystone. The proposed SA methods are compared against existing SA methods and validated using 19 independents test pile data. The proposed SA methods provide more accurate and consistent prediction of qs and qb, resulting in higher LRFD resistance and efficiency factors. The qs increases from 9.7 to 400% in siltstone and 5.9 to 87% in claystone at one day after the end of driving. However, pile relaxation is observed on qb of piles driven into siltstone, claystone and sandstone. [ABSTRACT FROM AUTHOR]