How Soils Can Help Predict High Rebound of Prestressed Concrete Displacement Piles-Article

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The paper examines how soil properties can help predict excessive rebound in large prestressed concrete displacement piles driven with single-acting hammers, particularly in Florida. Rebound commonly occurs at depths greater than about 15 m and can reduce mobilized end-bearing capacity, increase pile stresses, delay construction, and raise costs.

Researchers compared soil samples and pile-driving measurements from multiple Florida sites. They classified rebound greater than 12.5 mm per hammer blow as high and rebound below 6 mm as none, then evaluated grain size, soil classification, Atterberg limits, permeability, and cyclic triaxial behavior.

High rebound was associated with two principal soil types:

- <strong>Coarse-grained soils:</strong> very fine, poorly graded sands with silt, generally classified as SM. They tended to have more fines and silt than no-rebound sands; silt contents above roughly 20–25% and sand contents below 75% were useful warning signs. Clay content alone did not distinguish the groups.
- <strong>Fine-grained soils:</strong> highly plastic clays, generally classified as CH, with clay content around 50% and liquid limits near 75%. Their Atterberg-limit results typically plotted above the Casagrande chart’s A- and B-lines.

Rebound soils also had lower permeability and greater resilience under cyclic loading: they required more repeated load cycles to reach specified strains. This difference was especially pronounced in coarse-grained soils.

The authors recommend using 12.5 mm as the threshold for identifying high rebound in the pile conditions studied. For screening, they advise conducting grain-size analyses with hydrometer testing, classifying soils using the Unified Soil Classification System, and checking Atterberg limits in cohesive soils. Permeability and cyclic triaxial tests can provide additional evidence when needed. Soil type must be considered alongside deposit thickness, pile and hammer type, and hammer efficiency; rebound risk increases when piles penetrate sufficiently thick layers of susceptible soils.

Keywords

soil properties

pile rebound

prestressed concrete piles

Florida soils

grain size analysis

Unified Soil Classification System

Atterberg limits

permeability

cyclic triaxial tests

end-bearing capacity