Continuous Flight Auger Cast Piles for Bridge Foundations-PPT Presentation

PPT Presentation

Pdf Summary

The MD 152 Interchange–I-95 Northbound Express Toll Lane expansion in Harford County, Maryland, required a foundation alternative for Abutment B and its wingwalls. The original design used battered micropiles, but the abutment’s footprint had to remain unchanged, lateral deflection was limited to 0.5 inch, and a 108-inch water main lay about 20 feet away.<br /><br />The project replaced 107 micropiles with 119 vertical, 18-inch-diameter continuous flight auger (CFA) piles. Their estimated length was 40 feet, compared with an estimated 50-foot bond length for the micropiles. Design used subsurface data, FHWA guidance, service-load checks with a factor of safety of 2, and GROUP software to assess pile reactions, deflection, and fixity through phased construction. A sacrificial CFA test pile failed at 574 kips—287% of the 200-kip allowable load—and deflected 1.729 inches at failure.<br /><br />For the abutment, 18-inch CFA piles were reinforced with 11.75-inch N80 steel casing embedded to the calculated point of fixity. Structural checks produced a combined compression-and-flexure ratio of 0.97; additional reinforcement addressed uplift. Wingwalls retained their pile counts but required larger 24-inch CFA piles with steel pipe casing because 18-inch piles lacked sufficient structural capacity.<br /><br />Key lessons included coordinating casing procurement with the depth-to-fixity design, adding footing reinforcement for larger piles, and carefully evaluating buckling and lateral stability. The project highlighted the importance of matching pile diameter, reinforcement, and soil restraint to the structural demands.

Keywords

continuous flight auger piles

CFA piles

Harford County Maryland

MD 152 Interchange

I-95 Northbound Express Toll Lane

abutment foundation

wingwall piles

micropile replacement

lateral deflection

pile fixity