Piezocone Penetration Testing in Florida High Pile Rebound Soils-Article

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The study investigates high pile rebound (HPR)—large elastic upward movement with little permanent penetration during pile driving—which can cause false refusal, pile damage, delays, and inadequate capacity. Researchers evaluated 19 CPT/CPTu soundings at seven Florida Department of Transportation sites, comparing cone data with pile-driving analyzer measurements and laboratory soil classifications.

HPR occurred mainly in saturated, dense to very dense silty or clayey soils, commonly with fines content above 30%. At HPR layers, CPTu readings typically showed shoulder pore pressures above 20 tsf and friction ratios above 2%. Sites with little or acceptable rebound generally had pore pressures below 17 tsf and friction ratios below 2%, and were more sand-like. Cone resistance alone did not reliably predict rebound.

The CPT soil-behavior charts generally distinguished HPR from non-HPR soils; the Schmertmann, Eslami–Fellenius, and Schneider charts provided particularly useful separation. CPT interpretations agreed well with laboratory soil classifications. Rebound showed strong relationships with friction ratio and pore pressure, and the authors proposed a prediction equation using both parameters: <strong>R (in.) = 0.25Rf + 0.005u₂ − 0.05</strong>, where <em>Rf</em> is friction ratio (%) and <em>u₂</em> is pore pressure (tsf). The equation achieved an R² of about 0.80 in the study data, though some results from an external North Carolina case differed.

The authors recommend using CPT/CPTu behavior charts to identify potentially problematic soils when designing large displacement piles, and checking predicted rebound against field measurements.

Keywords

high pile rebound

HPR

CPT

CPTu

pile driving

pore pressure

friction ratio

soil behavior charts

Florida DOT

pile design