Lessons from the 2025 Mobile, AL, Prediction Survey-Article

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The 2025 Mobile, Alabama, pile-prediction survey gathered 74 independent predictions from 92 participants in 26 countries for a static loading test on an 18-inch concrete-filled steel pipe pile. Participants submitted predicted pile-head load–movement curves, assessed pile “capacity” using their own definitions, and estimated axial-force distributions.<br /><br />The survey had three stages. In the First Go, predictions were based on site investigation data. In the Second Go, participants received results from a nearby reference-pile test and could revise their submissions. In the Third Go, they assessed capacity from the actual test results.<br /><br />Predictions varied widely. In the First Go, the ratio between the highest and lowest reported capacities—and between movements at those capacities—was about 10. After the reference test, the capacity range narrowed to about fivefold, but the movement range remained about tenfold. Revised predictions and force distributions still showed substantial scatter. When participants assessed the measured test curve, capacity estimates were more consistent, yet the movement associated with capacity varied considerably.<br /><br />A central issue was the inconsistent meaning of “capacity”: participants used different criteria, including movement thresholds, the Davisson offset limit, and subjective curve interpretation. The author argues that this ambiguity makes capacity a weak and potentially misleading measure, particularly when design standards relate allowable loads directly to it.<br /><br />The survey also highlights that predictions depend on judgment, varied methods, and limited information; even a nearby reference test did not produce close agreement. The author recommends critically reviewing capacity-based design guidance and giving greater attention to pile movement and settlement, which are more directly relevant to foundation performance.

Keywords

pile prediction

Mobile Alabama

static loading test

concrete-filled steel pipe pile

pile capacity

load movement curves

axial force distribution

Davisson offset limit

foundation settlement

geotechnical survey