The Normalized Bearing Graph and Dynamic Reduction Function Concepts in Pile Acceptance-Paper

Paper

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The paper presents an improved method for accepting driven piles that have not been individually tested. It treats pile driving as an energy-capacity-movement relationship and argues that conventional driving formulas are unreliable when they use simplified models, uncertain hammer-energy assumptions, or static load tests performed after pile setup or relaxation has changed capacity.<br /><br />Using GRLWEAP wave-equation analyses, the author compares the Modified Hiley (Energy) Formula with predicted pile capacities across different hammer strokes and pile types. The uncorrected formula generally overestimates capacity. A single correction factor improves agreement only over a limited range of blow counts, because the formula estimates total driving resistance, which includes dynamic resistance as well as static resistance.<br /><br />The proposed Bearing Formula corrects the Energy Formula using a Dynamic Reduction Factor (DRF) that increases with pile set. The factor can be derived from wave-equation analysis or PDA testing. In two example studies—one involving a prestressed concrete pile and another a steel pipe pile—the corrected formula closely reproduces the wave-equation capacity-versus-blow-count curves.<br /><br />The paper also shows that a family of energy-dependent wave-equation bearing graphs can be converted into a normalized Relative Capacity Curve, with a separate capacity multiplier accounting for hammer energy. This offers a practical basis for improved on-site pile acceptance and monitoring. The author concludes that combining PDA testing with pile-driving monitoring can extend better construction control to all piles, while setup or relaxation after driving should be considered separately.

Keywords

pile driving

driving formulas

Modified Hiley Formula

wave-equation analysis

GRLWEAP

Dynamic Reduction Factor

bearing capacity

PDA testing

relative capacity curve

pile acceptance