Estimating Capacity and Reliability of Existing Foundations for Evaluation of Reuse-Article

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The paper evaluates methods for estimating the capacity and reliability of existing driven-pile foundations considered for reuse. Field research examined two Missouri bridges built in the late 1960s: one supported by precast concrete piles and the other by cast-in-place steel pipe piles. Investigations included historical records, geophysical pile-length testing, static load tests, dynamic restrike tests, and extraction and inspection of piles.<br /><br />Historical records and geophysical methods generally estimated pile lengths reasonably well. All 12 extracted piles were in excellent condition; corrosion on the cast-in-place piles caused no measurable section loss. Static load tests reached 1,200 kN for a precast pile and 1,100 kN for a cast-in-place pile, substantially exceeding the original documented design capacities. Dynamic testing produced similar, though generally lower-bound, estimates. Static calculation methods also predicted capacities above historical values, but results varied considerably.<br /><br />The study concludes that original plan capacities may be highly conservative and often have uncertain calculation methods and safety factors. Engineers should perform new capacity calculations at minimum, and use load testing where practical. Bayesian updating can combine calculated capacities with load-test evidence, while reliability analysis accounts for both capacity uncertainty and known loading. In this study, incorporating load-test information reduced uncertainty and yielded allowable resistances more than twice those based on static calculations alone.<br /><br />Overall, the findings show that targeted investigation can improve confidence in foundation reuse and prevent unnecessarily conservative designs. The authors also identify pile-length testing, historical performance records, and probabilistic reliability methods as useful tools for evaluating existing foundations.

Keywords

driven-pile foundations

foundation reuse

capacity estimation

reliability analysis

static load tests

dynamic restrike tests

pile-length testing

Bayesian updating

precast concrete piles

cast-in-place steel pipe piles