Full-Scale Testing of Seal Slab/Pile Interface Bond

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Title: Full-Scale Testing of Seal Slab/Pile Interface Bond

Author(s): G. Mullins, R. Sen, R. Sosa, and M. A. Issa

Publication: Special Publication

Volume: 211

Issue:

Appears on pages(s): 315-342

Keywords: bond stress; bond values; pile cap; pile walls; seal slab

Date: 2/1/2003

Abstract:
The construction of submerged or partially submerged pile caps often requires the use of a cast-in-place unreinforced slab referred to as a seal slab. This slab is cast underwater around piling and inside sheet pile walls to form the bottom of a cofferdam and withstand upward hydrostatic pressure. As the seal slab is only used for a relatively short period of time during placement of the reinforcing steel and concreting, its design has received little attention in refinement tending toward conservatism. Therein, the magnitude of available bond strength between the seal slab and piling to resist the uplift pressure has been poorly quantified and largely underutilized. This paper presents experimental results from 32 full-scale tests conducted to define the interface bond between cast-in-place concrete seal slabs and piling (sixteen 356 mm square prestressed concrete piles and sixteen 356 mm deep steel H-piles). Three different concrete placement environments--dry, fresh water, and bentonite slurry--were evaluated using the dry environment (where no fluid had to be displaced by the concrete) as the control. The effective seal slab thickness was varied between 0.5d and 2d, where d was either the width or depth of the pile section. Both "soil-caked" and normal, clean pile surfaces were investigated. Additionally, four of the sixteen concrete piles were cast with embedded gages located at the top, middle and bottom of the interface region to define the shear distribution. The study showed that: (1) significant bond stresses developed even for the worst placement environment, and (2) the entire embedded surface area should not be used in calculating the pile-to-seal slab bond capacity. Current design values in the Florida Department of Transportation specifications reflect the findings of this study.