Dynamic Load Testing of Non-Uniform Piles-Paper

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The paper examines the challenges of dynamically testing non-uniform piles, whose changes in material, cross-section, or geometry affect wave propagation and pile impedance. The traditional CASE method is fast and useful for real-time monitoring of uniform piles, but assumes uniform pile properties. Applying it to non-uniform piles can therefore produce misleading estimates of driving stresses and bearing resistance.<br /><br />Manual signal-matching methods can model complex pile configurations, but traditionally take too long for blow-by-blow field monitoring. The paper describes instant signal matching analysis implemented in the iN_GAPA program. It uses an iterative least-squares approach to fit simulated force and velocity signals to measured data. With modern computing, the analysis can run in a fraction of a second, enabling real-time monitoring without relying on a single lumped CASE damping value.<br /><br />The paper discusses wave-speed determination for composite and heterogeneous piles and notes that additional sensors may be needed when measurements from opposite sides are not representative. Case studies demonstrate the method on a tapered timber pile and a 155-foot hollow, spliced concrete pile. For the concrete pile, signal matching identified stress concentrations at transitions between solid and hollow sections. It estimated maximum compression stress of 4.01 ksi and maximum tension stress of 1.40 ksi—higher than the corresponding CASE estimates—and identified a likely integrity reflection at a mechanical splice.<br /><br />The authors conclude that instant signal matching can better represent the multiple sections, impedance changes, and possible bearing locations of non-uniform piles. It offers field engineers a way to monitor pile stresses and resistance during driving and may help prevent overstressing or misjudging pile capacity.

Keywords

non-uniform piles

dynamic testing

wave propagation

CASE method

signal matching

pile impedance

real-time monitoring

iterative least-squares

composite piles

bearing resistance