Seal Slab Prestressed Pile Interface Bond From Full-Scale Testing-PDF

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The study evaluated the bond between cast-in-place concrete seal slabs and prestressed concrete piles used in cofferdams. Researchers conducted one-third-scale model tests and 16 full-scale pullout tests, comparing control pours with concrete placed while displacing fresh water, salt water, or bentonite slurry. They also examined different pile embedment depths and soil-caked pile surfaces. Tests were performed after the seal concrete had cured for 72 hours.<br /><br />Measured bond stresses were substantially higher than the conservative values in existing specifications. In full-scale tests, average bond stresses ranged from 2.0–2.7 MPa for fresh-water placement and 1.5–2.5 MPa for bentonite placement; the lowest result, 1.1 MPa, came from a soil-caked pile embedded in bentonite. Bond stress generally decreased as embedment increased. Strain measurements showed that loads transferred through an effective bond depth approximately equal to the pile width, rather than uniformly across the full embedded length. Water flow during placement often washed soil caking from piles, while caking was more consequential in control and bentonite conditions.<br /><br />Pile and seal-slab cracking occurred during testing, indicating that structural capacity must be considered alongside interface bond. The authors recommend calculating pile bond capacity using an effective bond length limited to one pile width and checking that the resulting load does not exceed the pile’s tensile capacity. They propose allowable bond stresses of 2.1 MPa for concrete piles with fresh- or salt-water placement and 0.7 MPa for bentonite placement. The findings supported increased allowable values in Florida design guidance, potentially enabling thinner, less costly seal slabs.

Keywords

concrete seal slabs

prestressed concrete piles

cofferdam

bond stress

pullout tests

full-scale testing

bentonite slurry

embedment depth

effective bond length

tensile capacity