Innovative Drilled Shaft Installation Process Through Existing Bridge FoundationsÂ-Paper

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The Highway 146 bridge expansion over Clear Creek Channel in Houston encountered an unexpected obstruction when contractors tried to install driven piles. The obstruction was the massive, buried foundation of a bascule bridge demolished about 40 years earlier: reinforced-concrete pile caps and seal slabs supported by closely spaced precast piles. Existing records did not reveal what remained below the channel.<br /><br />Because the new bridge columns had to stay in their planned locations, alternatives such as reusing the old foundations, drilling many small holes for piles, or shifting the supports were impractical. TxDOT instead redesigned each affected foundation as a single 78-inch-diameter drilled shaft, up to 125 feet long. Each shaft had to be positioned within one inch of its column.<br /><br />Installation took place from barges in roughly 30 feet of water, where currents and tides made accurate drilling especially difficult. Contractors first used a large casing rotator and a 98-inch core barrel to cut through the old concrete and remove the material within the opening. They then installed a 72-foot permanent casing, excavated the soil and old piles inside it, and advanced the shaft to depth using bentonite slurry. Reinforcing cages were installed, and the shafts were concreted by tremie.<br /><br />The obstruction drilling required powerful equipment and specialized tools to cut through heavy reinforcement, old piles, and even a steel beam. The buried foundations were also found about five feet deeper than shown on the original plans, likely due to regional land subsidence.<br /><br />The multi-stage method enabled precise shaft placement despite the obstructions and marine conditions. The work was completed on time and within budget, with no safety incidents.

Keywords

Highway 146 bridge

Clear Creek Channel

Houston

bascule bridge foundation

driven piles obstruction

drilled shafts

barges

permanent casing

bentonite slurry

tremie concreting