Seal Slab/Steel Pile Interface Bond From Full-Scale Testing-PDF

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The study measured bond between cast-in-place concrete seal slabs and steel H-piles in cofferdams, addressing allowable shear values that had previously lacked experimental support. Researchers conducted eight one-third-scale pullout tests and 16 full-scale tests using W14 × 90 piles. Concrete was placed in dry control cofferdams, fresh water, or bentonite slurry; some tests also examined soil-caked pile surfaces. Pile embedment depths ranged from 0.5 to 2 times the pile depth. Specimens were tested after at least 72 hours of curing.<br /><br />Full-scale tests showed substantial bond, although less than in the model tests. Average bond stresses were approximately 1.1–1.3 MPa for fresh-water and control conditions, and 0.5–0.9 MPa for bentonite. The lowest result occurred with bentonite and a 2d embedment. Bond stress generally declined as embedment increased: beyond about one pile depth, additional embedment contributed little to pullout capacity. The authors attribute differences between model and full-scale results partly to the greater roughness of the model piles.<br /><br />Based on the full-scale results, the paper recommends calculating resistance over an effective bonded length no greater than one pile depth. Recommended allowable bond stresses are 1,000 kPa for steel piles placed in salt or fresh water and 350 kPa for piles placed in bentonite slurry. These values substantially exceed earlier design allowances and were incorporated into revised Florida Department of Transportation guidelines.

Keywords

cast-in-place concrete

steel H-piles

cofferdam bond

pullout tests

bond stress

embedment depth

bentonite slurry

fresh water

allowable shear

Florida DOT guidelines